geom.c

/* libctl: flexible Guile-based control files for scientific software
 * Copyright (C) 1998-2020 Massachusetts Institute of Technology and Steven G. Johnson
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA  02111-1307, USA.
 *
 * Steven G. Johnson can be contacted at stevenj@alum.mit.edu.
 */

#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdarg.h>

#ifndef LIBCTLGEOM
#include "ctl-io.h"
#else
#define material_type void *
static void material_type_copy(void **src, void **dest) { *dest = *src; }
#endif
#include "ctlgeom.h"

#ifdef CXX_CTL_IO
using namespace ctlio;
#define CTLIO ctlio::
#define GEOM geometric_object::
#define BLK block::
#define CYL cylinder::
#define MAT material_type::
#else
#define CTLIO
#define GEOM
#define BLK
#define CYL
#define MAT
#endif

#ifdef __cplusplus
#define MALLOC(type, num) (new type[num])
#define MALLOC1(type) (new type)
#define FREE(p) delete[](p)
#define FREE1(p) delete (p)
#else
#define MALLOC(type, num) ((type *)malloc(sizeof(type) * (num)))
#define MALLOC1(type) MALLOC(type, 1)
#define FREE(p) free(p)
#define FREE1(p) free(p)
#endif

#define K_PI 3.14159265358979323846
#define CHECK(cond, s)                                                                             \
  if (!(cond)) {                                                                                   \
    fprintf(stderr, s "\n");                                                                       \
    exit(EXIT_FAILURE);                                                                            \
  }

#define MAX(a, b) ((a) > (b) ? (a) : (b))
#define MIN(a, b) ((a) < (b) ? (a) : (b))

// forward declarations of prism-related routines, at the bottom of this file
static boolean node_in_polygon(double qx, double qy, vector3 *nodes, int num_nodes);
static boolean point_in_prism(prism *prsm, vector3 pc);
static vector3 normal_to_prism(prism *prsm, vector3 pc);
static double intersect_line_segment_with_prism(prism *prsm, vector3 pc, vector3 dc, double a,
                                                double b);
static double get_prism_volume(prism *prsm);
static void get_prism_bounding_box(prism *prsm, geom_box *box);
static void display_prism_info(int indentby, geometric_object *o);
static void init_prism(geometric_object *o);
/**************************************************************************/

/* Allows writing to Python's stdout when running from Meep's Python interface */
void (*ctl_printf_callback)(const char *s) = NULL;

void ctl_printf(const char *fmt, ...) {
  va_list ap;
  va_start(ap, fmt);
  if (ctl_printf_callback) {
    char *s;
    CHECK(vasprintf(&s, fmt, ap) >= 0, "vasprintf failed");
    ctl_printf_callback(s);
    free(s);
  }
  else {
    vprintf(fmt, ap);
    fflush(stdout);
  }
  va_end(ap);
}

/* If v is a vector in the lattice basis, normalize v so that
   its cartesian length is unity. */
static void lattice_normalize(vector3 *v) {
  *v = vector3_scale(
      1.0 / sqrt(vector3_dot(*v, matrix3x3_vector3_mult(geometry_lattice.metric, *v))), *v);
}

static vector3 lattice_to_cartesian(vector3 v) {
  return matrix3x3_vector3_mult(geometry_lattice.basis, v);
}

static vector3 cartesian_to_lattice(vector3 v) {
  return matrix3x3_vector3_mult(matrix3x3_inverse(geometry_lattice.basis), v);
}

/* geom_fix_object_ptr is called after an object's externally-configurable parameters
   have been initialized, but before any actual geometry calculations are done;
   it is an opportunity to (re)compute internal data fields (such as cached
   rotation matrices) that depend on externally-configurable parameters.

   One example: "Fix" the parameters of the given object to account for the
   geometry_lattice basis, which may be non-orthogonal.  In particular,
   this means that the normalization of several unit vectors, such
   as the cylinder or block axes, needs to be changed.

   Unfortunately, we can't do this stuff at object-creation time
   in Guile, because the geometry_lattice variable may not have
   been assigned to its final value at that point.  */
void geom_fix_object_ptr(geometric_object *o) {
  switch (o->which_subclass) {
    case GEOM CYLINDER:
      lattice_normalize(&o->subclass.cylinder_data->axis);
      if (o->subclass.cylinder_data->which_subclass == CYL WEDGE) {
        vector3 a = o->subclass.cylinder_data->axis;
        vector3 s = o->subclass.cylinder_data->subclass.wedge_data->wedge_start;
        double p = vector3_dot(s, matrix3x3_vector3_mult(geometry_lattice.metric, a));
        o->subclass.cylinder_data->subclass.wedge_data->e1 = vector3_minus(s, vector3_scale(p, a));
        lattice_normalize(&o->subclass.cylinder_data->subclass.wedge_data->e1);
        o->subclass.cylinder_data->subclass.wedge_data->e2 = cartesian_to_lattice(vector3_cross(
            lattice_to_cartesian(o->subclass.cylinder_data->axis),
            lattice_to_cartesian(o->subclass.cylinder_data->subclass.wedge_data->e1)));
      }
      break;
    case GEOM BLOCK: {
      matrix3x3 m;
      lattice_normalize(&o->subclass.block_data->e1);
      lattice_normalize(&o->subclass.block_data->e2);
      lattice_normalize(&o->subclass.block_data->e3);
      m.c0 = o->subclass.block_data->e1;
      m.c1 = o->subclass.block_data->e2;
      m.c2 = o->subclass.block_data->e3;
      o->subclass.block_data->projection_matrix = matrix3x3_inverse(m);
      break;
    }
    case GEOM PRISM: {
      init_prism(o);
      break;
    }
    case GEOM COMPOUND_GEOMETRIC_OBJECT: {
      int i;
      int n = o->subclass.compound_geometric_object_data->component_objects.num_items;
      geometric_object *os = o->subclass.compound_geometric_object_data->component_objects.items;
      for (i = 0; i < n; ++i) {
#if MATERIAL_TYPE_ABSTRACT
        if (os[i].material.which_subclass == MAT MATERIAL_TYPE_SELF)
          material_type_copy(&o->material, &os[i].material);
#endif
        geom_fix_object_ptr(os + i);
      }
      break;
    }
    case GEOM GEOMETRIC_OBJECT_SELF:
    case GEOM SPHERE: break; /* these objects are fine */
  }
}

// deprecated API — doesn't work for prisms
void geom_fix_object(geometric_object o) { geom_fix_object_ptr(&o); }

/* fix all objects in the geometry list as described in
   geom_fix_object, above */
void geom_fix_object_list(geometric_object_list geometry) {
  int index;

  for (index = 0; index < geometry.num_items; ++index)
    geom_fix_object_ptr(geometry.items + index);
}

void geom_fix_objects0(geometric_object_list geometry) { geom_fix_object_list(geometry); }

void geom_fix_objects(void) { geom_fix_object_list(geometry); }

void geom_fix_lattice0(lattice *L) {
  L->basis1 = unit_vector3(L->basis1);
  L->basis2 = unit_vector3(L->basis2);
  L->basis3 = unit_vector3(L->basis3);
  L->b1 = vector3_scale(L->basis_size.x, L->basis1);
  L->b2 = vector3_scale(L->basis_size.y, L->basis2);
  L->b3 = vector3_scale(L->basis_size.z, L->basis3);
  L->basis.c0 = L->b1;
  L->basis.c1 = L->b2;
  L->basis.c2 = L->b3;
  L->metric = matrix3x3_mult(matrix3x3_transpose(L->basis), L->basis);
}

void geom_fix_lattice(void) { geom_fix_lattice0(&geometry_lattice); }

void geom_cartesian_lattice0(lattice *L) {
  L->basis1.x = 1;
  L->basis1.y = 0;
  L->basis1.z = 0;
  L->basis2.x = 0;
  L->basis2.y = 1;
  L->basis2.z = 0;
  L->basis3.x = 0;
  L->basis3.y = 0;
  L->basis3.z = 1;
  L->basis_size.x = L->basis_size.y = L->basis_size.z = 1;
  geom_fix_lattice0(L);
}

void geom_cartesian_lattice(void) { geom_cartesian_lattice0(&geometry_lattice); }

void geom_initialize(void) {
  /* initialize many of the input variables that are normally
     initialized from Scheme, except for default_material and
     geometry_lattice.size. */
  geom_cartesian_lattice();
  geometry_center.x = geometry_center.y = geometry_center.z = 0;
  dimensions = 3;
  ensure_periodicity = 1;
  geometry.num_items = 0;
  geometry.items = 0;
}

/**************************************************************************/

/* Return whether or not the point p (in the lattice basis) is inside
   the object o.

   Requires that the global input var geometry_lattice already be
   initialized.

   point_in_fixed_objectp additionally requires that geom_fix_object
   has been called on o (if the lattice basis is non-orthogonal).  */

boolean CTLIO point_in_objectp(vector3 p, geometric_object o) {
  geom_fix_object_ptr(&o);
  return point_in_fixed_objectp(p, o);
}

boolean point_in_fixed_objectp(vector3 p, geometric_object o) {
  return point_in_fixed_pobjectp(p, &o);
}

/* as point_in_fixed_objectp, but sets o to the object in question (if true)
   (which may be different from the input o if o is a compound object) */
boolean point_in_fixed_pobjectp(vector3 p, geometric_object *o) {
  vector3 r = vector3_minus(p, o->center);

  switch (o->which_subclass) {
    case GEOM GEOMETRIC_OBJECT_SELF: return 0;
    case GEOM SPHERE: {
      number radius = o->subclass.sphere_data->radius;
      return (radius > 0.0 && vector3_dot(r, matrix3x3_vector3_mult(geometry_lattice.metric, r)) <=
                                  radius * radius);
    }
    case GEOM CYLINDER: {
      vector3 rm = matrix3x3_vector3_mult(geometry_lattice.metric, r);
      number proj = vector3_dot(o->subclass.cylinder_data->axis, rm);
      number height = o->subclass.cylinder_data->height;
      if (fabs(proj) <= 0.5 * height) {
        number radius = o->subclass.cylinder_data->radius;
        if (o->subclass.cylinder_data->which_subclass == CYL CONE)
          radius += (proj / height + 0.5) *
                    (o->subclass.cylinder_data->subclass.cone_data->radius2 - radius);
        else if (o->subclass.cylinder_data->which_subclass == CYL WEDGE) {
          number x = vector3_dot(rm, o->subclass.cylinder_data->subclass.wedge_data->e1);
          number y = vector3_dot(rm, o->subclass.cylinder_data->subclass.wedge_data->e2);
          number theta = atan2(y, x);
          number wedge_angle = o->subclass.cylinder_data->subclass.wedge_data->wedge_angle;
          if (wedge_angle > 0) {
            if (theta < 0) theta = theta + 2 * K_PI;
            if (theta > wedge_angle) return 0;
          }
          else {
            if (theta > 0) theta = theta - 2 * K_PI;
            if (theta < wedge_angle) return 0;
          }
        }
        return (radius != 0.0 && vector3_dot(r, rm) - proj * proj <= radius * radius);
      }
      else
        return 0;
    }
    case GEOM BLOCK: {
      vector3 proj = matrix3x3_vector3_mult(o->subclass.block_data->projection_matrix, r);
      switch (o->subclass.block_data->which_subclass) {
        case BLK BLOCK_SELF: {
          vector3 size = o->subclass.block_data->size;
          return (fabs(proj.x) <= 0.5 * size.x && fabs(proj.y) <= 0.5 * size.y &&
                  fabs(proj.z) <= 0.5 * size.z);
        }
        case BLK ELLIPSOID: {
          vector3 isa = o->subclass.block_data->subclass.ellipsoid_data->inverse_semi_axes;
          double a = proj.x * isa.x, b = proj.y * isa.y, c = proj.z * isa.z;
          return (a * a + b * b + c * c <= 1.0);
        }
      }
      break; // never get here but silence compiler warning
    }
    case GEOM PRISM: {
      return point_in_prism(o->subclass.prism_data, p);
    }
    case GEOM COMPOUND_GEOMETRIC_OBJECT: {
      int i;
      int n = o->subclass.compound_geometric_object_data->component_objects.num_items;
      geometric_object *os = o->subclass.compound_geometric_object_data->component_objects.items;
      vector3 shiftby = o->center;
      for (i = 0; i < n; ++i) {
        *o = os[i];
        o->center = vector3_plus(o->center, shiftby);
        if (point_in_fixed_pobjectp(p, o)) return 1;
      }
      break;
    }
  }
  return 0;
}

/**************************************************************************/

/* convert a point p inside o to a coordinate in [0,1]^3 that
   is some "natural" coordinate for the object */
vector3 to_geom_object_coords(vector3 p, geometric_object o) {
  const vector3 half = {0.5, 0.5, 0.5};
  vector3 r = vector3_minus(p, o.center);

  switch (o.which_subclass) {
    default: {
      vector3 po = {0, 0, 0};
      return po;
    }
    case GEOM SPHERE: {
      number radius = o.subclass.sphere_data->radius;
      return vector3_plus(half, vector3_scale(0.5 / radius, r));
    }
    /* case GEOM CYLINDER:
       NOT YET IMPLEMENTED */
    case GEOM BLOCK: {
      vector3 proj = matrix3x3_vector3_mult(o.subclass.block_data->projection_matrix, r);
      vector3 size = o.subclass.block_data->size;
      if (size.x != 0.0) proj.x /= size.x;
      if (size.y != 0.0) proj.y /= size.y;
      if (size.z != 0.0) proj.z /= size.z;
      return vector3_plus(half, proj);
    }
      /* case GEOM PRISM:
          NOT YET IMPLEMENTED */
  }
}

/* inverse of to_geom_object_coords */
vector3 from_geom_object_coords(vector3 p, geometric_object o) {
  const vector3 half = {0.5, 0.5, 0.5};
  p = vector3_minus(p, half);
  switch (o.which_subclass) {
    default: return o.center;
    case GEOM SPHERE: {
      number radius = o.subclass.sphere_data->radius;
      return vector3_plus(o.center, vector3_scale(radius / 0.5, p));
    }
    /* case GEOM CYLINDER:
       NOT YET IMPLEMENTED */
    case GEOM BLOCK: {
      vector3 size = o.subclass.block_data->size;
      return vector3_plus(
          o.center,
          vector3_plus(vector3_scale(size.x * p.x, o.subclass.block_data->e1),
                       vector3_plus(vector3_scale(size.y * p.y, o.subclass.block_data->e2),
                                    vector3_scale(size.z * p.z, o.subclass.block_data->e3))));
    }
      /* case GEOM PRISM:
          NOT YET IMPLEMENTED */
  }
}

/**************************************************************************/
/* Return the normal vector from the given object to the given point,
   in lattice coordinates, using the surface of the object that the
   point is "closest" to for some definition of "closest" that is
   reasonable (at least for points near to the object). The length and
   sign of the normal vector are arbitrary. */

vector3 CTLIO normal_to_object(vector3 p, geometric_object o) {
  geom_fix_object_ptr(&o);
  return normal_to_fixed_object(p, o);
}

vector3 normal_to_fixed_object(vector3 p, geometric_object o) {
  vector3 r = vector3_minus(p, o.center);

  switch (o.which_subclass) {

    case GEOM CYLINDER: {
      vector3 rm = matrix3x3_vector3_mult(geometry_lattice.metric, r);
      double proj = vector3_dot(o.subclass.cylinder_data->axis, rm),
             height = o.subclass.cylinder_data->height, radius, prad;
      if (fabs(proj) > height * 0.5) return o.subclass.cylinder_data->axis;
      radius = o.subclass.cylinder_data->radius;
      prad = sqrt(fabs(vector3_dot(r, rm) - proj * proj));
      if (o.subclass.cylinder_data->which_subclass == CYL CONE)
        radius += (proj / height + 0.5) *
                  (o.subclass.cylinder_data->subclass.cone_data->radius2 - radius);
      if (fabs(fabs(proj) - height * 0.5) < fabs(prad - radius))
        return o.subclass.cylinder_data->axis;
      if (o.subclass.cylinder_data->which_subclass == CYL CONE)
        return vector3_minus(
            r, vector3_scale(
                   proj + prad * (o.subclass.cylinder_data->subclass.cone_data->radius2 - radius) /
                              height,
                   o.subclass.cylinder_data->axis));
      else
        return vector3_minus(r, vector3_scale(proj, o.subclass.cylinder_data->axis));
    } // case GEOM CYLINDER

    case GEOM BLOCK: {
      vector3 proj = matrix3x3_vector3_mult(o.subclass.block_data->projection_matrix, r);
      switch (o.subclass.block_data->which_subclass) {
        case BLK BLOCK_SELF: {
          vector3 size = o.subclass.block_data->size;
          double d1 = fabs(fabs(proj.x) - 0.5 * size.x);
          double d2 = fabs(fabs(proj.y) - 0.5 * size.y);
          double d3 = fabs(fabs(proj.z) - 0.5 * size.z);
          if (d1 < d2 && d1 < d3)
            return matrix3x3_row1(o.subclass.block_data->projection_matrix);
          else if (d2 < d3)
            return matrix3x3_row2(o.subclass.block_data->projection_matrix);
          else
            return matrix3x3_row3(o.subclass.block_data->projection_matrix);
        } // case BLK BLOCK_SELF

        case BLK ELLIPSOID:
        default: {
          vector3 isa = o.subclass.block_data->subclass.ellipsoid_data->inverse_semi_axes;
          proj.x *= isa.x * isa.x;
          proj.y *= isa.y * isa.y;
          proj.z *= isa.z * isa.z;
          return matrix3x3_transpose_vector3_mult(o.subclass.block_data->projection_matrix, proj);
        } // case BLK ELLIPSOID

      } // switch (o.subclass.block_data->which_subclass)

    } // case GEOM BLOCK

    case GEOM PRISM: return normal_to_prism(o.subclass.prism_data, p);

    default: return r;
  } // switch (o.which_subclass)

  return r; // never get here
}

/**************************************************************************/

/* Here is a useful macro to loop over different possible shifts of
   the lattice vectors.  body is executed for each possible shift,
   where the shift is given by the value of shiftby (which should
   be a vector3 variable).  I would much rather make this a function,
   but C's lack of lambda-like function construction or closures makes
   this easier to do as a macro.  (One could at least wish for
   an easier way to make multi-line macros.)  */

#define LOOP_PERIODIC(shiftby, body)                                                               \
  {                                                                                                \
    switch (dimensions) {                                                                          \
      case 1: {                                                                                    \
        int iii;                                                                                   \
        shiftby.y = shiftby.z = 0;                                                                 \
        for (iii = -1; iii <= 1; ++iii) {                                                          \
          shiftby.x = iii * geometry_lattice.size.x;                                               \
          body;                                                                                    \
        }                                                                                          \
        break;                                                                                     \
      }                                                                                            \
      case 2: {                                                                                    \
        int iii, jjj;                                                                              \
        shiftby.z = 0;                                                                             \
        for (iii = -1; iii <= 1; ++iii) {                                                          \
          shiftby.x = iii * geometry_lattice.size.x;                                               \
          for (jjj = -1; jjj <= 1; ++jjj) {                                                        \
            shiftby.y = jjj * geometry_lattice.size.y;                                             \
            body;                                                                                  \
          }                                                                                        \
        }                                                                                          \
        break;                                                                                     \
      }                                                                                            \
      case 3: {                                                                                    \
        int iii, jjj, kkk;                                                                         \
        for (iii = -1; iii <= 1; ++iii) {                                                          \
          shiftby.x = iii * geometry_lattice.size.x;                                               \
          for (jjj = -1; jjj <= 1; ++jjj) {                                                        \
            shiftby.y = jjj * geometry_lattice.size.y;                                             \
            for (kkk = -1; kkk <= 1; ++kkk) {                                                      \
              shiftby.z = kkk * geometry_lattice.size.z;                                           \
              body;                                                                                \
              if (geometry_lattice.size.z == 0) break;                                             \
            }                                                                                      \
            if (geometry_lattice.size.y == 0) break;                                               \
          }                                                                                        \
          if (geometry_lattice.size.x == 0) break;                                                 \
        }                                                                                          \
        break;                                                                                     \
      }                                                                                            \
    }                                                                                              \
  }

/**************************************************************************/

/* Like point_in_objectp, but also checks the object shifted
   by the lattice vectors: */

boolean CTLIO point_in_periodic_objectp(vector3 p, geometric_object o) {
  geom_fix_object_ptr(&o);
  return point_in_periodic_fixed_objectp(p, o);
}

boolean point_in_periodic_fixed_objectp(vector3 p, geometric_object o) {
  vector3 shiftby;
  LOOP_PERIODIC(shiftby, if (point_in_fixed_objectp(vector3_minus(p, shiftby), o)) return 1);
  return 0;
}

boolean point_shift_in_periodic_fixed_pobjectp(vector3 p, geometric_object *o, vector3 *shiftby) {
  geometric_object o0 = *o;
  LOOP_PERIODIC((*shiftby), {
    *o = o0;
    if (point_in_fixed_pobjectp(vector3_minus(p, *shiftby), o)) return 1;
  });
  return 0;
}

/**************************************************************************/

/* Functions to return the object or material type corresponding to
   the point p (in the lattice basis).  Returns default_material if p
   is not in any object.

   Requires that the global input vars geometry_lattice, geometry,
   dimensions, default_material and ensure_periodicity already be
   initialized.

   Also requires that geom_fix_objects() has been called!

   material_of_point_inobject is a variant that also returns whether
   or not the point was in any object.  */

geometric_object object_of_point0(geometric_object_list geometry, vector3 p, vector3 *shiftby) {
  geometric_object o;
  int index;
  shiftby->x = shiftby->y = shiftby->z = 0;
  /* loop in reverse order so that later items are given precedence: */
  for (index = geometry.num_items - 1; index >= 0; --index) {
    o = geometry.items[index];
    if ((ensure_periodicity && point_shift_in_periodic_fixed_pobjectp(p, &o, shiftby)) ||
        point_in_fixed_pobjectp(p, &o))
      return o;
  }
  o.which_subclass = GEOM GEOMETRIC_OBJECT_SELF; /* no object found */
  return o;
}

geometric_object object_of_point(vector3 p, vector3 *shiftby) {
  return object_of_point0(geometry, p, shiftby);
}

material_type material_of_point_inobject0(geometric_object_list geometry, vector3 p,
                                          boolean *inobject) {
  vector3 shiftby;
  geometric_object o = object_of_point0(geometry, p, &shiftby);
  *inobject = o.which_subclass != GEOM GEOMETRIC_OBJECT_SELF;
  ;
  return (*inobject ? o.material : default_material);
}

material_type material_of_point_inobject(vector3 p, boolean *inobject) {
  return material_of_point_inobject0(geometry, p, inobject);
}

material_type material_of_point0(geometric_object_list geometry, vector3 p) {
  boolean inobject;
  return material_of_point_inobject0(geometry, p, &inobject);
}

material_type material_of_point(vector3 p) { return material_of_point0(geometry, p); }

/**************************************************************************/

/* Given a geometric object o, display some information about it,
   indented by indentby spaces. */

void CTLIO display_geometric_object_info(int indentby, geometric_object o) {
  geom_fix_object_ptr(&o);
  ctl_printf("%*s", indentby, "");
  switch (o.which_subclass) {
    case GEOM CYLINDER:
      switch (o.subclass.cylinder_data->which_subclass) {
        case CYL WEDGE: ctl_printf("wedge"); break;
        case CYL CONE: ctl_printf("cone"); break;
        case CYL CYLINDER_SELF: ctl_printf("cylinder"); break;
      }
      break;
    case GEOM SPHERE: ctl_printf("sphere"); break;
    case GEOM BLOCK:
      switch (o.subclass.block_data->which_subclass) {
        case BLK ELLIPSOID: ctl_printf("ellipsoid"); break;
        case BLK BLOCK_SELF: ctl_printf("block"); break;
      }
      break;
    case GEOM PRISM: ctl_printf("prism"); break;
    case GEOM COMPOUND_GEOMETRIC_OBJECT: ctl_printf("compound object"); break;
    default: ctl_printf("geometric object"); break;
  }
  ctl_printf(", center = (%g,%g,%g)\n", o.center.x, o.center.y, o.center.z);
  switch (o.which_subclass) {
    case GEOM CYLINDER:
      ctl_printf("%*s     radius %g, height %g, axis (%g, %g, %g)\n", indentby, "",
                 o.subclass.cylinder_data->radius, o.subclass.cylinder_data->height,
                 o.subclass.cylinder_data->axis.x, o.subclass.cylinder_data->axis.y,
                 o.subclass.cylinder_data->axis.z);
      if (o.subclass.cylinder_data->which_subclass == CYL CONE)
        ctl_printf("%*s     radius2 %g\n", indentby, "",
                   o.subclass.cylinder_data->subclass.cone_data->radius2);
      else if (o.subclass.cylinder_data->which_subclass == CYL WEDGE)
        ctl_printf("%*s     wedge-theta %g\n", indentby, "",
                   o.subclass.cylinder_data->subclass.wedge_data->wedge_angle);
      break;
    case GEOM SPHERE:
      ctl_printf("%*s     radius %g\n", indentby, "", o.subclass.sphere_data->radius);
      break;
    case GEOM BLOCK:
      ctl_printf("%*s     size (%g,%g,%g)\n", indentby, "", o.subclass.block_data->size.x,
                 o.subclass.block_data->size.y, o.subclass.block_data->size.z);
      ctl_printf(
          "%*s     axes (%g,%g,%g), (%g,%g,%g), (%g,%g,%g)\n", indentby, "",
          o.subclass.block_data->e1.x, o.subclass.block_data->e1.y, o.subclass.block_data->e1.z,
          o.subclass.block_data->e2.x, o.subclass.block_data->e2.y, o.subclass.block_data->e2.z,
          o.subclass.block_data->e3.x, o.subclass.block_data->e3.y, o.subclass.block_data->e3.z);
      break;
    case GEOM PRISM: display_prism_info(indentby, &o); break;
    case GEOM COMPOUND_GEOMETRIC_OBJECT: {
      int i;
      int n = o.subclass.compound_geometric_object_data->component_objects.num_items;
      geometric_object *os = o.subclass.compound_geometric_object_data->component_objects.items;
      ctl_printf("%*s     %d components:\n", indentby, "", n);
      for (i = 0; i < n; ++i)
        display_geometric_object_info(indentby + 5, os[i]);
      break;
    }
    default: break;
  }
}

/**************************************************************************/

/* Compute the intersections with o of a line along p+s*d, returning
   the number of intersections (at most 2) and the two intersection "s"
   values in s[0] and s[1].   (Note: o must not be a compound object.) */
int intersect_line_with_object(vector3 p, vector3 d, geometric_object o, double s[2]) {
  p = vector3_minus(p, o.center);
  s[0] = s[1] = 0;
  switch (o.which_subclass) {
    case GEOM SPHERE: {
      number radius = o.subclass.sphere_data->radius;
      vector3 dm = matrix3x3_vector3_mult(geometry_lattice.metric, d);
      double a = vector3_dot(d, dm);
      double b2 = -vector3_dot(dm, p);
      double c =
          vector3_dot(p, matrix3x3_vector3_mult(geometry_lattice.metric, p)) - radius * radius;
      double discrim = b2 * b2 - a * c;
      if (discrim < 0)
        return 0;
      else if (discrim == 0) {
        s[0] = b2 / a;
        return 1;
      }
      else {
        discrim = sqrt(discrim);
        s[0] = (b2 + discrim) / a;
        s[1] = (b2 - discrim) / a;
        return 2;
      }
    } // case GEOM SPHERE
    case GEOM CYLINDER: {
      vector3 dm = matrix3x3_vector3_mult(geometry_lattice.metric, d);
      vector3 pm = matrix3x3_vector3_mult(geometry_lattice.metric, p);
      number height = o.subclass.cylinder_data->height;
      number radius = o.subclass.cylinder_data->radius;
      number radius2 = o.subclass.cylinder_data->which_subclass == CYL CONE
                           ? o.subclass.cylinder_data->subclass.cone_data->radius2
                           : radius;
      double dproj = vector3_dot(o.subclass.cylinder_data->axis, dm);
      double pproj = vector3_dot(o.subclass.cylinder_data->axis, pm);
      double D = (radius2 - radius) / height;
      double L = radius + (radius2 - radius) * 0.5 + pproj * D;
      double a = vector3_dot(d, dm) - dproj * dproj * (1 + D * D);
      double b2 = dproj * (pproj + D * L) - vector3_dot(p, dm);
      double c = vector3_dot(p, pm) - pproj * pproj - L * L;
      double discrim = b2 * b2 - a * c;
      int ret;
      if (a == 0) { /* linear equation */
        if (b2 == 0) {
          if (c == 0) { /* infinite intersections */
            s[0] = ((height * 0.5) - pproj) / dproj;
            s[1] = -((height * 0.5) + pproj) / dproj;
            return 2;
          }
          else
            ret = 0;
        }
        else {
          s[0] = 0.5 * c / b2;
          ret = 1;
        }
      }
      else if (discrim < 0)
        ret = 0;
      else if (discrim == 0) {
        s[0] = b2 / a;
        ret = 1;
      }
      else {
        discrim = sqrt(discrim);
        s[0] = (b2 + discrim) / a;
        s[1] = (b2 - discrim) / a;
        ret = 2;
      }
      if (ret == 2 && fabs(pproj + s[1] * dproj) > height * 0.5) ret = 1;
      if (ret >= 1 && fabs(pproj + s[0] * dproj) > height * 0.5) {
        --ret;
        s[0] = s[1];
      }
      if (ret == 2 || dproj == 0) return ret;
      /* find intersections with endcaps */
      s[ret] = (height * 0.5 - pproj) / dproj;
      if (a * s[ret] * s[ret] - 2 * b2 * s[ret] + c <= 0) ++ret;
      if (ret < 2) {
        s[ret] = -(height * 0.5 + pproj) / dproj;
        if (a * s[ret] * s[ret] - 2 * b2 * s[ret] + c <= 0) ++ret;
      }
      if (ret == 2 && s[0] == s[1]) ret = 1;
      return ret;
    } // case GEOM CYLINDER
    case GEOM BLOCK: {
      vector3 dproj = matrix3x3_vector3_mult(o.subclass.block_data->projection_matrix, d);
      vector3 pproj = matrix3x3_vector3_mult(o.subclass.block_data->projection_matrix, p);
      switch (o.subclass.block_data->which_subclass) {
        case BLK BLOCK_SELF: {
          vector3 size = o.subclass.block_data->size;
          int ret = 0;
          size.x *= 0.5;
          size.y *= 0.5;
          size.z *= 0.5;
          if (dproj.x != 0) {
            s[ret] = (size.x - pproj.x) / dproj.x;
            if (fabs(pproj.y + s[ret] * dproj.y) <= size.y &&
                fabs(pproj.z + s[ret] * dproj.z) <= size.z)
              ++ret;
            s[ret] = (-size.x - pproj.x) / dproj.x;
            if (fabs(pproj.y + s[ret] * dproj.y) <= size.y &&
                fabs(pproj.z + s[ret] * dproj.z) <= size.z)
              ++ret;
            if (ret == 2) return 2;
          }
          if (dproj.y != 0) {
            s[ret] = (size.y - pproj.y) / dproj.y;
            if (fabs(pproj.x + s[ret] * dproj.x) <= size.x &&
                fabs(pproj.z + s[ret] * dproj.z) <= size.z)
              ++ret;
            if (ret == 2) return 2;
            s[ret] = (-size.y - pproj.y) / dproj.y;
            if (fabs(pproj.x + s[ret] * dproj.x) <= size.x &&
                fabs(pproj.z + s[ret] * dproj.z) <= size.z)
              ++ret;
            if (ret == 2) return 2;
          }
          if (dproj.z != 0) {
            s[ret] = (size.z - pproj.z) / dproj.z;
            if (fabs(pproj.x + s[ret] * dproj.x) <= size.x &&
                fabs(pproj.y + s[ret] * dproj.y) <= size.y)
              ++ret;
            if (ret == 2) return 2;
            s[ret] = (-size.z - pproj.z) / dproj.z;
            if (fabs(pproj.x + s[ret] * dproj.x) <= size.x &&
                fabs(pproj.y + s[ret] * dproj.y) <= size.y)
              ++ret;
          }
          return ret;
        } // case BLK BLOCK_SELF:

        case BLK ELLIPSOID:
        default: {
          vector3 isa = o.subclass.block_data->subclass.ellipsoid_data->inverse_semi_axes;
          double a, b2, c, discrim;
          dproj.x *= isa.x;
          dproj.y *= isa.y;
          dproj.z *= isa.z;
          pproj.x *= isa.x;
          pproj.y *= isa.y;
          pproj.z *= isa.z;
          a = vector3_dot(dproj, dproj);
          b2 = -vector3_dot(dproj, pproj);
          c = vector3_dot(pproj, pproj) - 1;
          discrim = b2 * b2 - a * c;
          if (discrim < 0)
            return 0;
          else if (discrim == 0) {
            s[0] = b2 / a;
            return 1;
          }
          else {
            discrim = sqrt(discrim);
            s[0] = (b2 + discrim) / a;
            s[1] = (b2 - discrim) / a;
            return 2;
          }
        } // case BLK BLOCK_SELF, default

      } // switch (o.subclass.block_data->which_subclass)

    } // case GEOM BLOCK
    default: return 0;
  }
}

/* Compute the intersections with o of a line along p+s*d in the interval s in [a,b], returning
    the length of the s intersection in this interval.  (Note: o must not be a compound object.) */
double intersect_line_segment_with_object(vector3 p, vector3 d, geometric_object o, double a,
                                          double b) {
  if (o.which_subclass == GEOM PRISM) {
    return intersect_line_segment_with_prism(o.subclass.prism_data, p, d, a, b);
  }
  else {
    double s[2];
    if (2 == intersect_line_with_object(p, d, o, s)) {
      double ds = (s[0] < s[1] ? MIN(s[1], b) - MAX(s[0], a) : MIN(s[0], b) - MAX(s[1], a));
      return (ds > 0 ? ds : 0.0);
    }
    else
      return 0.0;
  }
}

/**************************************************************************/

/* Given a basis (matrix columns are the basis unit vectors) and the
   size of the lattice (in basis vectors), returns a new "square"
   basis.  This corresponds to a region of the same volume, but made
   rectangular, suitable for outputing to an HDF file.

   Given a vector in the range (0..1, 0..1, 0..1), multiplying by
   the square basis matrix will yield the coordinates of a point
   in the rectangular volume, given in the lattice basis. */

matrix3x3 CTLIO square_basis(matrix3x3 basis, vector3 size) {
  matrix3x3 square;

  square.c0 = basis.c0;

  square.c1 = vector3_minus(basis.c1, vector3_scale(vector3_dot(basis.c0, basis.c1), basis.c1));

  square.c2 = vector3_minus(basis.c2, vector3_scale(vector3_dot(basis.c0, basis.c2), basis.c2));
  square.c2 = vector3_minus(
      square.c2, vector3_scale(vector3_dot(basis.c0, square.c2), unit_vector3(square.c2)));

  square.c0 = vector3_scale(size.x, square.c0);
  square.c1 = vector3_scale(size.y, square.c1);
  square.c2 = vector3_scale(size.z, square.c2);

  return matrix3x3_mult(matrix3x3_inverse(basis), square);
}

/**************************************************************************/

/* compute the 3d volume enclosed by a geometric object o. */

double geom_object_volume(GEOMETRIC_OBJECT o) {
  switch (o.which_subclass) {
    case GEOM SPHERE: {
      number radius = o.subclass.sphere_data->radius;
      return (1.333333333333333333 * K_PI) * radius * radius * radius;
    }
    case GEOM CYLINDER: {
      number height = o.subclass.cylinder_data->height;
      number radius = o.subclass.cylinder_data->radius;
      number radius2 = o.subclass.cylinder_data->which_subclass == CYL CONE
                           ? o.subclass.cylinder_data->subclass.cone_data->radius2
                           : radius;
      double vol = height * (K_PI / 3) * (radius * radius + radius * radius2 + radius2 * radius2);
      if (o.subclass.cylinder_data->which_subclass == CYL WEDGE)
        return vol * fabs(o.subclass.cylinder_data->subclass.wedge_data->wedge_angle) / (2 * K_PI);
      else
        return vol;
    }
    case GEOM BLOCK: {
      vector3 size = o.subclass.block_data->size;
      double vol = size.x * size.y * size.z *
                   fabs(matrix3x3_determinant(geometry_lattice.basis) /
                        matrix3x3_determinant(o.subclass.block_data->projection_matrix));
      return o.subclass.block_data->which_subclass == BLK BLOCK_SELF ? vol : vol * (K_PI / 6);
    }
    case GEOM PRISM: {
      return get_prism_volume(o.subclass.prism_data);
    }
    default: return 0; /* unsupported object types? */
  }
}

/**************************************************************************/
/**************************************************************************/

/* Fast geometry routines */

/* Using the above material_of_point routine is way too slow, especially
   when there are lots of objects to test.  Thus, we develop the following
   replacement routines.

   The basic idea here is twofold.  (1) Compute bounding boxes for
   each geometric object, for which inclusion tests can be computed
   quickly.  (2) Build a tree that recursively breaks down the unit cell
   in half, allowing us to perform searches in logarithmic time. */

/**************************************************************************/

/* geom_box utilities: */
static void geom_box_union(geom_box *bu, const geom_box *b1, const geom_box *b2) {
  bu->low.x = MIN(b1->low.x, b2->low.x);
  bu->low.y = MIN(b1->low.y, b2->low.y);
  bu->low.z = MIN(b1->low.z, b2->low.z);
  bu->high.x = MAX(b1->high.x, b2->high.x);
  bu->high.y = MAX(b1->high.y, b2->high.y);
  bu->high.z = MAX(b1->high.z, b2->high.z);
}

static void geom_box_intersection(geom_box *bi, const geom_box *b1, const geom_box *b2) {
  bi->low.x = MAX(b1->low.x, b2->low.x);
  bi->low.y = MAX(b1->low.y, b2->low.y);
  bi->low.z = MAX(b1->low.z, b2->low.z);
  bi->high.x = MIN(b1->high.x, b2->high.x);
  bi->high.y = MIN(b1->high.y, b2->high.y);
  bi->high.z = MIN(b1->high.z, b2->high.z);
}

static void geom_box_add_pt(geom_box *b, vector3 p) {
  b->low.x = MIN(b->low.x, p.x);
  b->low.y = MIN(b->low.y, p.y);
  b->low.z = MIN(b->low.z, p.z);
  b->high.x = MAX(b->high.x, p.x);
  b->high.y = MAX(b->high.y, p.y);
  b->high.z = MAX(b->high.z, p.z);
}

#define BETWEEN(x, low, high) ((x) >= (low) && (x) <= (high))

static int geom_box_contains_point(const geom_box *b, vector3 p) {
  return (BETWEEN(p.x, b->low.x, b->high.x) && BETWEEN(p.y, b->low.y, b->high.y) &&
          BETWEEN(p.z, b->low.z, b->high.z));
}

/* return whether or not the given two boxes intersect */
static int geom_boxes_intersect(const geom_box *b1, const geom_box *b2) {
  /* true if the x, y, and z ranges all intersect. */
  return (
      (BETWEEN(b1->low.x, b2->low.x, b2->high.x) || BETWEEN(b1->high.x, b2->low.x, b2->high.x) ||
       BETWEEN(b2->low.x, b1->low.x, b1->high.x)) &&
      (BETWEEN(b1->low.y, b2->low.y, b2->high.y) || BETWEEN(b1->high.y, b2->low.y, b2->high.y) ||
       BETWEEN(b2->low.y, b1->low.y, b1->high.y)) &&
      (BETWEEN(b1->low.z, b2->low.z, b2->high.z) || BETWEEN(b1->high.z, b2->low.z, b2->high.z) ||
       BETWEEN(b2->low.z, b1->low.z, b1->high.z)));
}

static void geom_box_shift(geom_box *b, vector3 shiftby) {
  b->low = vector3_plus(b->low, shiftby);
  b->high = vector3_plus(b->high, shiftby);
}

/**************************************************************************/

/* Computing a bounding box for a geometric object: */

/* compute | (b x c) / (a * (b x c)) |, for use below */
static number compute_dot_cross(vector3 a, vector3 b, vector3 c) {
  vector3 bxc = vector3_cross(b, c);
  return fabs(vector3_norm(bxc) / vector3_dot(a, bxc));
}

/* Compute a bounding box for the object o, preferably the smallest
   bounding box.  The box is a parallelepiped with axes given by
   the geometry lattice vectors, and its corners are given in the
   lattice basis.

   Requires that geometry_lattice global has been initialized,
   etcetera.  */
void geom_get_bounding_box(geometric_object o, geom_box *box) {
  geom_fix_object_ptr(&o);

  /* initialize to empty box at the center of the object: */
  box->low = box->high = o.center;

  switch (o.which_subclass) {
    case GEOM GEOMETRIC_OBJECT_SELF: break;
    case GEOM SPHERE: {
      /* Find the parallelepiped that the sphere inscribes.
         The math comes out surpisingly simple--try it! */

      number radius = o.subclass.sphere_data->radius;
      /* actually, we could achieve the same effect here
         by inverting the geometry_lattice.basis matrix... */
      number r1 =
          compute_dot_cross(geometry_lattice.b1, geometry_lattice.b2, geometry_lattice.b3) * radius;
      number r2 =
          compute_dot_cross(geometry_lattice.b2, geometry_lattice.b3, geometry_lattice.b1) * radius;
      number r3 =
          compute_dot_cross(geometry_lattice.b3, geometry_lattice.b1, geometry_lattice.b2) * radius;
      box->low.x -= r1;
      box->low.y -= r2;
      box->low.z -= r3;
      box->high.x += r1;
      box->high.y += r2;
      box->high.z += r3;
      break;
    }
    case GEOM CYLINDER: {
      /* Find the bounding boxes of the two (circular) ends of
         the cylinder, then take the union.  Again, the math
         for finding the bounding parallelepiped of a circle
         comes out suprisingly simple in the end.  Proof left
         as an exercise for the reader. */

      number radius = o.subclass.cylinder_data->radius;
      number h = o.subclass.cylinder_data->height * 0.5;
      vector3 axis = /* cylinder axis in cartesian coords */
          matrix3x3_vector3_mult(geometry_lattice.basis, o.subclass.cylinder_data->axis);
      vector3 e12 = vector3_cross(geometry_lattice.basis1, geometry_lattice.basis2);
      vector3 e23 = vector3_cross(geometry_lattice.basis2, geometry_lattice.basis3);
      vector3 e31 = vector3_cross(geometry_lattice.basis3, geometry_lattice.basis1);
      number elen2, eproj;
      number r1, r2, r3;
      geom_box tmp_box;

      /* Find bounding box dimensions, in lattice coords,
         for the circular ends of the cylinder: */

      elen2 = vector3_dot(e23, e23);
      eproj = vector3_dot(e23, axis);
      r1 = fabs(sqrt(fabs(elen2 - eproj * eproj)) / vector3_dot(e23, geometry_lattice.b1));

      elen2 = vector3_dot(e31, e31);
      eproj = vector3_dot(e31, axis);
      r2 = fabs(sqrt(fabs(elen2 - eproj * eproj)) / vector3_dot(e31, geometry_lattice.b2));

      elen2 = vector3_dot(e12, e12);
      eproj = vector3_dot(e12, axis);
      r3 = fabs(sqrt(fabs(elen2 - eproj * eproj)) / vector3_dot(e12, geometry_lattice.b3));

      /* Get axis in lattice coords: */
      axis = o.subclass.cylinder_data->axis;

      tmp_box = *box; /* set tmp_box to center of object */

      /* bounding box for -h*axis cylinder end: */
      box->low.x -= h * axis.x + r1 * radius;
      box->low.y -= h * axis.y + r2 * radius;
      box->low.z -= h * axis.z + r3 * radius;
      box->high.x -= h * axis.x - r1 * radius;
      box->high.y -= h * axis.y - r2 * radius;
      box->high.z -= h * axis.z - r3 * radius;

      if (o.subclass.cylinder_data->which_subclass == CYL CONE)
        radius = fabs(o.subclass.cylinder_data->subclass.cone_data->radius2);

      /* bounding box for +h*axis cylinder end: */
      tmp_box.low.x += h * axis.x - r1 * radius;
      tmp_box.low.y += h * axis.y - r2 * radius;
      tmp_box.low.z += h * axis.z - r3 * radius;
      tmp_box.high.x += h * axis.x + r1 * radius;
      tmp_box.high.y += h * axis.y + r2 * radius;
      tmp_box.high.z += h * axis.z + r3 * radius;

      geom_box_union(box, box, &tmp_box);
      break;
    }
    case GEOM BLOCK: {
      /* blocks are easy: just enlarge the box to be big enough to
         contain all 8 corners of the block. */

      vector3 s1 = vector3_scale(o.subclass.block_data->size.x, o.subclass.block_data->e1);
      vector3 s2 = vector3_scale(o.subclass.block_data->size.y, o.subclass.block_data->e2);
      vector3 s3 = vector3_scale(o.subclass.block_data->size.z, o.subclass.block_data->e3);
      vector3 corner =
          vector3_plus(o.center, vector3_scale(-0.5, vector3_plus(s1, vector3_plus(s2, s3))));

      geom_box_add_pt(box, corner);
      geom_box_add_pt(box, vector3_plus(corner, s1));
      geom_box_add_pt(box, vector3_plus(corner, s2));
      geom_box_add_pt(box, vector3_plus(corner, s3));
      geom_box_add_pt(box, vector3_plus(corner, vector3_plus(s1, s2)));
      geom_box_add_pt(box, vector3_plus(corner, vector3_plus(s1, s3)));
      geom_box_add_pt(box, vector3_plus(corner, vector3_plus(s3, s2)));
      geom_box_add_pt(box, vector3_plus(corner, vector3_plus(s1, vector3_plus(s2, s3))));
      break;
    }
    case GEOM PRISM: {
      get_prism_bounding_box(o.subclass.prism_data, box);
      break;
    }
    case GEOM COMPOUND_GEOMETRIC_OBJECT: {
      int i;
      int n = o.subclass.compound_geometric_object_data->component_objects.num_items;
      geometric_object *os = o.subclass.compound_geometric_object_data->component_objects.items;
      for (i = 0; i < n; ++i) {
        geom_box boxi;
        geom_get_bounding_box(os[i], &boxi);
        geom_box_shift(&boxi, o.center);
        geom_box_union(box, box, &boxi);
      }
      break;
    }
  }
}

/**************************************************************************/
/* Compute the fraction of a box's volume (or area/length in 2d/1d) that
   overlaps an object.   Instead of a box, we also allow an ellipsoid
   inscribed inside the box (or a skewed ellipsoid if the box is not
   orthogonal). */

typedef struct {
  geometric_object o;
  vector3 p, dir;
  int pdim[2];   /* the (up to two) integration directions */
  double scx[2]; /* scale factor (e.g. sign flip) for x coordinates */
  unsigned dim;
  double a0, b0;        /* box limits along analytic direction */
  int is_ellipsoid;     /* 0 for box, 1 for ellipsoid */
  double winv[2], c[2]; /* ellipsoid width-inverses/centers in int. dirs */
  double w0, c0;        /* width/center along analytic direction */
} overlap_data;

static double overlap_integrand(integer ndim, number *x, void *data_) {
  overlap_data *data = (overlap_data *)data_;
  double s[2];
  const double *scx = data->scx;
  vector3 p = data->p;
  double a0 = data->a0, b0 = data->b0;
  double scale_result = 1.0;

  if (ndim > 0) {
    switch (data->pdim[0]) {
      case 0: p.x = scx[0] * x[0]; break;
      case 1: p.y = scx[0] * x[0]; break;
      case 2: p.z = scx[0] * x[0]; break;
    }
    if (ndim > 1) {
      switch (data->pdim[1]) {
        case 0: p.x = scx[1] * x[1]; break;
        case 1: p.y = scx[1] * x[1]; break;
        case 2: p.z = scx[1] * x[1]; break;
      }
    }
  }

  if (data->is_ellipsoid && ndim > 0) {
    /* compute width of ellipsoid at this point, along the
       analytic-intersection direction */
    double dx = (x[0] - data->c[0]) * data->winv[0];
    double w = 1.0 - dx * dx;
    if (ndim > 1) { /* rescale 2nd dimension to stay inside ellipsoid */
      double x1;
      if (w < 0) return 0.0; /* outside the ellipsoid */
      scale_result = sqrt(w);
      x1 = data->c[1] + (x[1] - data->c[1]) * scale_result;
      switch (data->pdim[1]) {
        case 0: p.x = scx[1] * x1; break;
        case 1: p.y = scx[1] * x1; break;
        case 2: p.z = scx[1] * x1; break;
      }
      dx = (x1 - data->c[1]) * data->winv[1];
      w -= dx * dx;
    }
    if (w < 0) return 0.0; /* outside the ellipsoid */
    w = data->w0 * sqrt(w);
    a0 = data->c0 - w;
    b0 = data->c0 + w;
  }

  return intersect_line_segment_with_object(p, data->dir, data->o, a0, b0) * scale_result;
}

number overlap_with_object(geom_box b, int is_ellipsoid, geometric_object o, number tol,
                           integer maxeval) {
  overlap_data data;
  int empty_x = b.low.x == b.high.x;
  int empty_y = b.low.y == b.high.y;
  int empty_z = b.low.z == b.high.z;
  double V0 = ((empty_x ? 1 : b.high.x - b.low.x) * (empty_y ? 1 : b.high.y - b.low.y) *
               (empty_z ? 1 : b.high.z - b.low.z));
  vector3 ex = {1, 0, 0}, ey = {0, 1, 0}, ez = {0, 0, 1};
  geom_box bb;
  double xmin[2] = {0, 0}, xmax[2] = {0, 0}, esterr;
  int errflag;
  unsigned i;

  geom_get_bounding_box(o, &bb);
  if (!is_ellipsoid && !empty_x && !empty_y && !empty_z && /* todo: optimize 1d and 2d cases */
      bb.low.x >= b.low.x && bb.high.x <= b.high.x && bb.low.y >= b.low.y &&
      bb.high.y <= b.high.y && bb.low.z >= b.low.z && bb.high.z <= b.high.z)
    return geom_object_volume(o) /
           (V0 * fabs(matrix3x3_determinant(
                     geometry_lattice.basis))); /* o is completely contained within b */
  geom_box_intersection(&bb, &b, &bb);
  if (bb.low.x > bb.high.x || bb.low.y > bb.high.y || bb.low.z > bb.high.z ||
      (!empty_x && bb.low.x == bb.high.x) || (!empty_y && bb.low.y == bb.high.y) ||
      (!empty_z && bb.low.z == bb.high.z))
    return 0.0;

  data.winv[0] = data.winv[1] = data.w0 = 1.0;
  data.c[0] = data.c[1] = data.c0 = 0;

  data.o = o;
  data.p.x = data.p.y = data.p.z = 0;
  data.dim = 0;
  if (!empty_x) {
    data.dir = ex;
    data.a0 = bb.low.x;
    data.b0 = bb.high.x;
    data.w0 = 0.5 * (b.high.x - b.low.x);
    data.c0 = 0.5 * (b.high.x + b.low.x);
    if (!empty_y) {
      xmin[data.dim] = bb.low.y;
      xmax[data.dim] = bb.high.y;
      data.winv[data.dim] = 2.0 / (b.high.y - b.low.y);
      data.c[data.dim] = 0.5 * (b.high.y + b.low.y);
      data.pdim[data.dim++] = 1;
    }
    if (!empty_z) {
      xmin[data.dim] = bb.low.z;
      xmax[data.dim] = bb.high.z;
      data.winv[data.dim] = 2.0 / (b.high.z - b.low.z);
      data.c[data.dim] = 0.5 * (b.high.z + b.low.z);
      data.pdim[data.dim++] = 2;
    }
  }
  else if (!empty_y) {
    data.dir = ey;
    data.a0 = bb.low.y;
    data.b0 = bb.high.y;
    data.w0 = 0.5 * (b.high.y - b.low.y);
    data.c0 = 0.5 * (b.high.y + b.low.y);
    if (!empty_x) {
      xmin[data.dim] = bb.low.x;
      xmax[data.dim] = bb.high.x;
      data.winv[data.dim] = 2.0 / (b.high.x - b.low.x);
      data.c[data.dim] = 0.5 * (b.high.x + b.low.x);
      data.pdim[data.dim++] = 0;
    }
    if (!empty_z) {
      xmin[data.dim] = bb.low.z;
      xmax[data.dim] = bb.high.z;
      data.winv[data.dim] = 2.0 / (b.high.z - b.low.z);
      data.c[data.dim] = 0.5 * (b.high.z + b.low.z);
      data.pdim[data.dim++] = 2;
    }
  }
  else if (!empty_z) {
    data.dir = ez;
    data.a0 = bb.low.z;
    data.b0 = bb.high.z;
    data.w0 = 0.5 * (b.high.z - b.low.z);
    data.c0 = 0.5 * (b.high.z + b.low.z);
    if (!empty_x) {
      xmin[data.dim] = bb.low.x;
      xmax[data.dim] = bb.high.x;
      data.winv[data.dim] = 2.0 / (b.high.x - b.low.x);
      data.c[data.dim] = 0.5 * (b.high.x + b.low.x);
      data.pdim[data.dim++] = 0;
    }
    if (!empty_y) {
      xmin[data.dim] = bb.low.y;
      xmax[data.dim] = bb.high.y;
      data.winv[data.dim] = 2.0 / (b.high.y - b.low.y);
      data.c[data.dim] = 0.5 * (b.high.y + b.low.y);
      data.pdim[data.dim++] = 1;
    }
  }
  else
    return 1.0;

#if 1
  /* To maintain mirror symmetries through the x/y/z axes, we flip
     the integration range whenever xmax < 0.  (This is in case
     the integration routine is not fully symmetric, which may
     happen(?) due to the upper bound on the #evaluations.)*/
  for (i = 0; i < data.dim; ++i) {
    if (xmax[i] < 0) {
      double xm = xmin[i];
      data.scx[i] = -1;
      xmin[i] = -xmax[i];
      xmax[i] = -xm;
      data.c[i] = -data.c[i];
    }
    else
      data.scx[i] = 1;
  }
#else
  for (i = 0; i < data.dim; ++i)
    data.scx[i] = 1;
#endif

  if ((data.is_ellipsoid = is_ellipsoid)) { /* data for ellipsoid calc. */
    if (data.dim == 1)
      V0 *= K_PI / 4;
    else if (data.dim == 2)
      V0 *= K_PI / 6;
  }

  return adaptive_integration(overlap_integrand, xmin, xmax, data.dim, &data, 0.0, tol, maxeval,
                              &esterr, &errflag) /
         V0;
}

number box_overlap_with_object(geom_box b, geometric_object o, number tol, integer maxeval) {
  return overlap_with_object(b, 0, o, tol, maxeval);
}

number ellipsoid_overlap_with_object(geom_box b, geometric_object o, number tol, integer maxeval) {
  return overlap_with_object(b, 1, o, tol, maxeval);
}

number CTLIO range_overlap_with_object(vector3 low, vector3 high, geometric_object o, number tol,
                                       integer maxeval) {
  geom_box b;
  b.low = low;
  b.high = high;
  return box_overlap_with_object(b, o, tol, maxeval);
}

/**************************************************************************/

/* geom_box_tree: a tree of boxes and the objects contained within
   them.  The tree recursively partitions the unit cell, allowing us
   to perform binary searches for the object containing a given point. */

void destroy_geom_box_tree(geom_box_tree t) {
  if (t) {
    destroy_geom_box_tree(t->t1);
    destroy_geom_box_tree(t->t2);
    if (t->objects) FREE(t->objects);
    FREE1(t);
  }
}

/* return whether the object o, shifted by the vector shiftby,
   possibly intersects b.  Upon return, obj_b is the bounding
   box for o. */
static int object_in_box(geometric_object o, vector3 shiftby, geom_box *obj_b, const geom_box *b) {
  geom_get_bounding_box(o, obj_b);
  geom_box_shift(obj_b, shiftby);
  return geom_boxes_intersect(obj_b, b);
}

static geom_box_tree new_geom_box_tree(void) {
  geom_box_tree t;

  t = MALLOC1(struct geom_box_tree_struct);
  CHECK(t, "out of memory");
  t->t1 = t->t2 = NULL;
  t->nobjects = 0;
  t->objects = NULL;
  return t;
}

/* Divide b into b1 and b2, cutting b in two along the axis
   divide_axis (0 = x, 1 = y, 2 = z) at divide_point. */
static void divide_geom_box(const geom_box *b, int divide_axis, number divide_point, geom_box *b1,
                            geom_box *b2) {
  *b1 = *b2 = *b;
  switch (divide_axis) {
    case 0: b1->high.x = b2->low.x = divide_point; break;
    case 1: b1->high.y = b2->low.y = divide_point; break;
    case 2: b1->high.z = b2->low.z = divide_point; break;
  }
}

#define VEC_I(v, i) ((i) == 0 ? (v).x : ((i) == 1 ? (v).y : (v).z))
#define SMALL 1.0e-7

/* Find the best place (best_partition) to "cut" along the axis
   divide_axis in order to maximally divide the objects between
   the partitions.  Upon return, n1 and n2 are the number of objects
   below and above the partition, respectively. */
static void find_best_partition(int nobjects, const geom_box_object *objects, int divide_axis,
                                number *best_partition, int *n1, int *n2) {
  number cur_partition;
  int i, j, cur_n1, cur_n2;

  *n1 = *n2 = nobjects + 1;
  *best_partition = 0;

  /* Search for the best partition, by checking all possible partitions
     either just above the high end of an object or just below the
     low end of an object. */

  for (i = 0; i < nobjects; ++i) {
    cur_partition = VEC_I(objects[i].box.high, divide_axis) * (1 + SMALL);
    cur_n1 = cur_n2 = 0;
    for (j = 0; j < nobjects; ++j) {
      double low = VEC_I(objects[j].box.low, divide_axis);
      double high = VEC_I(objects[j].box.high, divide_axis);
      cur_n1 += low <= cur_partition;
      cur_n2 += high >= cur_partition;
    }
    CHECK(cur_n1 + cur_n2 >= nobjects, "assertion failure 1 in find_best_partition");
    if (MAX(cur_n1, cur_n2) < MAX(*n1, *n2)) {
      *best_partition = cur_partition;
      *n1 = cur_n1;
      *n2 = cur_n2;
    }
  }
  for (i = 0; i < nobjects; ++i) {
    cur_partition = VEC_I(objects[i].box.low, divide_axis) * (1 - SMALL);
    cur_n1 = cur_n2 = 0;
    for (j = 0; j < nobjects; ++j) {
      double low = VEC_I(objects[j].box.low, divide_axis);
      double high = VEC_I(objects[j].box.high, divide_axis);
      cur_n1 += low <= cur_partition;
      cur_n2 += high >= cur_partition;
    }
    CHECK(cur_n1 + cur_n2 >= nobjects, "assertion failure 2 in find_best_partition");
    if (MAX(cur_n1, cur_n2) < MAX(*n1, *n2)) {
      *best_partition = cur_partition;
      *n1 = cur_n1;
      *n2 = cur_n2;
    }
  }
}

/* divide_geom_box_tree: recursively divide t in two, each time
   dividing along the axis that maximally partitions the boxes,
   and only stop partitioning when partitioning doesn't help any
   more.  Upon return, t points to the partitioned tree. */
static void divide_geom_box_tree(geom_box_tree t) {
  int division_nobjects[3][2] = {{0, 0}, {0, 0}, {0, 0}};
  number division_point[3];
  int best = -1;
  int i, j, n1, n2;

  if (!t) return;
  if (t->t1 || t->t2) { /* this node has already been divided */
    divide_geom_box_tree(t->t1);
    divide_geom_box_tree(t->t2);
    return;
  }

  if (t->nobjects <= 2) return; /* no point in partitioning */

  /* Try partitioning along each dimension, counting the
     number of objects in the partitioned boxes and finding
     the best partition. */
  for (i = 0; i < dimensions; ++i) {
    if (VEC_I(t->b.high, i) == VEC_I(t->b.low, i)) continue; /* skip empty dimensions */
    find_best_partition(t->nobjects, t->objects, i, &division_point[i], &division_nobjects[i][0],
                        &division_nobjects[i][1]);
    if (best < 0 || MAX(division_nobjects[i][0], division_nobjects[i][1]) <
                        MAX(division_nobjects[best][0], division_nobjects[best][1]))
      best = i;
  }

  /* don't do anything if division makes the worst case worse or if
     it fails to improve the best case: */
  if (best < 0 || MAX(division_nobjects[best][0], division_nobjects[best][1]) + 1 > t->nobjects ||
      MIN(division_nobjects[best][0], division_nobjects[best][1]) + 1 >= t->nobjects)
    return; /* division didn't help us */

  divide_geom_box(&t->b, best, division_point[best], &t->b1, &t->b2);
  t->t1 = new_geom_box_tree();
  t->t2 = new_geom_box_tree();
  t->t1->b = t->b1;
  t->t2->b = t->b2;

  t->t1->nobjects = division_nobjects[best][0];
  t->t1->objects = MALLOC(geom_box_object, t->t1->nobjects);
  CHECK(t->t1->objects, "out of memory");

  t->t2->nobjects = division_nobjects[best][1];
  t->t2->objects = MALLOC(geom_box_object, t->t2->nobjects);
  CHECK(t->t2->objects, "out of memory");

  for (j = n1 = n2 = 0; j < t->nobjects; ++j) {
    if (geom_boxes_intersect(&t->b1, &t->objects[j].box)) {
      CHECK(n1 < t->t1->nobjects, "BUG in divide_geom_box_tree");
      t->t1->objects[n1++] = t->objects[j];
    }
    if (geom_boxes_intersect(&t->b2, &t->objects[j].box)) {
      CHECK(n2 < t->t2->nobjects, "BUG in divide_geom_box_tree");
      t->t2->objects[n2++] = t->objects[j];
    }
  }
  CHECK(j == t->nobjects && n1 == t->t1->nobjects && n2 == t->t2->nobjects,
        "BUG in divide_geom_box_tree: wrong nobjects");

  t->nobjects = 0;
  FREE(t->objects);
  t->objects = NULL;

  divide_geom_box_tree(t->t1);
  divide_geom_box_tree(t->t2);
}

geom_box_tree create_geom_box_tree(void) {
  geom_box b0;
  b0.low = vector3_plus(geometry_center, vector3_scale(-0.5, geometry_lattice.size));
  b0.high = vector3_plus(geometry_center, vector3_scale(0.5, geometry_lattice.size));
  return create_geom_box_tree0(geometry, b0);
}

static int num_objects_in_box(const geometric_object *o, vector3 shiftby, const geom_box *b) {
  if (o->which_subclass == GEOM COMPOUND_GEOMETRIC_OBJECT) {
    int n = o->subclass.compound_geometric_object_data->component_objects.num_items;
    geometric_object *os = o->subclass.compound_geometric_object_data->component_objects.items;
    int i, sum = 0;
    shiftby = vector3_plus(shiftby, o->center);
    for (i = 0; i < n; ++i)
      sum += num_objects_in_box(os + i, shiftby, b);
    return sum;
  }
  else {
    geom_box ob;
    return object_in_box(*o, shiftby, &ob, b);
  }
}

static int store_objects_in_box(const geometric_object *o, vector3 shiftby, const geom_box *b,
                                geom_box_object *bo, int precedence) {
  if (o->which_subclass == GEOM COMPOUND_GEOMETRIC_OBJECT) {
    int n = o->subclass.compound_geometric_object_data->component_objects.num_items;
    geometric_object *os = o->subclass.compound_geometric_object_data->component_objects.items;
    int i, sum = 0;
    shiftby = vector3_plus(shiftby, o->center);
    for (i = 0; i < n; ++i)
      sum += store_objects_in_box(os + i, shiftby, b, bo + sum, precedence - sum);
    return sum;
  }
  else {
    geom_box ob;
    if (object_in_box(*o, shiftby, &ob, b)) {
      bo->box = ob;
      bo->o = o;
      bo->shiftby = shiftby;
      bo->precedence = precedence;
      return 1;
    }
    else
      return 0;
  }
}

geom_box_tree create_geom_box_tree0(geometric_object_list geometry, geom_box b0) {
  geom_box_tree t = new_geom_box_tree();
  int i, index;

  t->b = b0;

  for (i = geometry.num_items - 1; i >= 0; --i) {
    vector3 shiftby = {0, 0, 0};
    if (ensure_periodicity) {
      LOOP_PERIODIC(shiftby, t->nobjects += num_objects_in_box(geometry.items + i, shiftby, &t->b));
    }
    else
      t->nobjects += num_objects_in_box(geometry.items + i, shiftby, &t->b);
  }

  t->objects = MALLOC(geom_box_object, t->nobjects);
  CHECK(t->objects || t->nobjects == 0, "out of memory");

  for (i = geometry.num_items - 1, index = 0; i >= 0; --i) {
    vector3 shiftby = {0, 0, 0};
    if (ensure_periodicity) {
      int precedence = t->nobjects - index;
      LOOP_PERIODIC(shiftby, index += store_objects_in_box(geometry.items + i, shiftby, &t->b,
                                                           t->objects + index, precedence));
    }
    else
      index += store_objects_in_box(geometry.items + i, shiftby, &t->b, t->objects + index,
                                    t->nobjects - index);
  }
  CHECK(index == t->nobjects, "bug in create_geom_box_tree0");

  divide_geom_box_tree(t);

  return t;
}

/* create a new tree from t, pruning all nodes that don't intersect b */
geom_box_tree restrict_geom_box_tree(geom_box_tree t, const geom_box *b) {
  geom_box_tree tr;
  int i, j;

  if (!t || !geom_boxes_intersect(&t->b, b)) return NULL;

  tr = new_geom_box_tree();

  for (i = 0, j = 0; i < t->nobjects; ++i)
    if (geom_boxes_intersect(&t->objects[i].box, b)) ++j;
  tr->nobjects = j;
  tr->objects = MALLOC(geom_box_object, tr->nobjects);
  CHECK(tr->objects || tr->nobjects == 0, "out of memory");

  for (i = 0, j = 0; i < t->nobjects; ++i)
    if (geom_boxes_intersect(&t->objects[i].box, b)) tr->objects[j++] = t->objects[i];

  tr->t1 = restrict_geom_box_tree(t->t1, b);
  tr->t2 = restrict_geom_box_tree(t->t2, b);

  if (tr->nobjects == 0) {
    if (tr->t1 && !tr->t2) {
      geom_box_tree tr0 = tr;
      tr = tr->t1;
      FREE1(tr0);
    }
    else if (tr->t2 && !tr->t1) {
      geom_box_tree tr0 = tr;
      tr = tr->t2;
      FREE1(tr0);
    }
  }

  return tr;
}

/**************************************************************************/

/* recursively search the tree for the given point, returning the
   subtree (if any) that contains it and the index oindex of the
   object in that tree.  The input value of oindex indicates the
   starting object to search in t (0 to search all). */
static geom_box_tree tree_search(vector3 p, geom_box_tree t, int *oindex) {
  int i;
  geom_box_tree gbt;

  if (!t || !geom_box_contains_point(&t->b, p)) return NULL;

  for (i = *oindex; i < t->nobjects; ++i)
    if (geom_box_contains_point(&t->objects[i].box, p) &&
        point_in_fixed_objectp(vector3_minus(p, t->objects[i].shiftby), *t->objects[i].o)) {
      *oindex = i;
      return t;
    }

  *oindex = 0;
  gbt = tree_search(p, t->t1, oindex);
  if (!gbt) gbt = tree_search(p, t->t2, oindex);
  return gbt;
}

/* shift p to be within the unit cell of the lattice (centered on the
   origin) */
vector3 shift_to_unit_cell(vector3 p) {
  while (p.x >= 0.5 * geometry_lattice.size.x)
    p.x -= geometry_lattice.size.x;
  while (p.x < -0.5 * geometry_lattice.size.x)
    p.x += geometry_lattice.size.x;
  while (p.y >= 0.5 * geometry_lattice.size.y)
    p.y -= geometry_lattice.size.y;
  while (p.y < -0.5 * geometry_lattice.size.y)
    p.y += geometry_lattice.size.y;
  while (p.z >= 0.5 * geometry_lattice.size.z)
    p.z -= geometry_lattice.size.z;
  while (p.z < -0.5 * geometry_lattice.size.z)
    p.z += geometry_lattice.size.z;
  return p;
}

const geometric_object *object_of_point_in_tree(vector3 p, geom_box_tree t, vector3 *shiftby,
                                                int *precedence) {
  int oindex = 0;
  t = tree_search(p, t, &oindex);
  if (t) {
    geom_box_object *gbo = t->objects + oindex;
    *shiftby = gbo->shiftby;
    *precedence = gbo->precedence;
    return gbo->o;
  }
  else {
    shiftby->x = shiftby->y = shiftby->z = 0;
    *precedence = 0;
    return 0;
  }
}

material_type material_of_unshifted_point_in_tree_inobject(vector3 p, geom_box_tree t,
                                                           boolean *inobject) {
  int oindex = 0;
  t = tree_search(p, t, &oindex);
  if (t) {
    *inobject = 1;
    return (t->objects[oindex].o->material);
  }
  else {
    *inobject = 0;
    return default_material;
  }
}

material_type material_of_point_in_tree_inobject(vector3 p, geom_box_tree t, boolean *inobject) {
  /* backwards compatibility */
  return material_of_unshifted_point_in_tree_inobject(shift_to_unit_cell(p), t, inobject);
}

material_type material_of_point_in_tree(vector3 p, geom_box_tree t) {
  boolean inobject;
  return material_of_point_in_tree_inobject(p, t, &inobject);
}

geom_box_tree geom_tree_search_next(vector3 p, geom_box_tree t, int *oindex) {
  *oindex += 1; /* search starting at next oindex */
  return tree_search(p, t, oindex);
}

geom_box_tree geom_tree_search(vector3 p, geom_box_tree t, int *oindex) {
  *oindex = -1; /* search all indices > -1 */
  return geom_tree_search_next(p, t, oindex);
}

/**************************************************************************/

/* convert a vector p in the given object to some coordinate
   in [0,1]^3 that is a more "natural" map of the object interior. */
vector3 to_geom_box_coords(vector3 p, geom_box_object *gbo) {
  return to_geom_object_coords(vector3_minus(p, gbo->shiftby), *gbo->o);
}

/**************************************************************************/

void display_geom_box_tree(int indentby, geom_box_tree t) {
  int i;

  if (!t) return;
  ctl_printf("%*sbox (%g..%g, %g..%g, %g..%g)\n", indentby, "", t->b.low.x, t->b.high.x, t->b.low.y,
             t->b.high.y, t->b.low.z, t->b.high.z);
  for (i = 0; i < t->nobjects; ++i) {
    ctl_printf("%*sbounding box (%g..%g, %g..%g, %g..%g)\n", indentby + 5, "",
               t->objects[i].box.low.x, t->objects[i].box.high.x, t->objects[i].box.low.y,
               t->objects[i].box.high.y, t->objects[i].box.low.z, t->objects[i].box.high.z);
    ctl_printf("%*sshift object by (%g, %g, %g)\n", indentby + 5, "", t->objects[i].shiftby.x,
               t->objects[i].shiftby.y, t->objects[i].shiftby.z);
    display_geometric_object_info(indentby + 5, *t->objects[i].o);
  }
  display_geom_box_tree(indentby + 5, t->t1);
  display_geom_box_tree(indentby + 5, t->t2);
}

/**************************************************************************/

/* Computing tree statistics (depth and number of nodes): */

/* helper function for geom_box_tree_stats */
static void get_tree_stats(geom_box_tree t, int *depth, int *nobjects) {
  if (t) {
    int d1, d2;

    *nobjects += t->nobjects;
    d1 = d2 = *depth + 1;
    get_tree_stats(t->t1, &d1, nobjects);
    get_tree_stats(t->t2, &d2, nobjects);
    *depth = MAX(d1, d2);
  }
}

void geom_box_tree_stats(geom_box_tree t, int *depth, int *nobjects) {
  *depth = *nobjects = 0;
  get_tree_stats(t, depth, nobjects);
}

/**************************************************************************/

#ifndef LIBCTLGEOM

vector3 get_grid_size(void) {
  return ctl_convert_vector3_to_c(gh_call0(gh_lookup("get-grid-size")));
}

vector3 get_resolution(void) {
  return ctl_convert_vector3_to_c(gh_call0(gh_lookup("get-resolution")));
}

void get_grid_size_n(int *nx, int *ny, int *nz) {
  vector3 grid_size;
  grid_size = get_grid_size();
  *nx = (int)grid_size.x;
  *ny = (int)grid_size.y;
  *nz = (int)grid_size.z;
}

#endif

/**************************************************************************/

/* constructors for the geometry types (ugh, wish these
   could be automatically generated from geom.scm) */

geometric_object make_geometric_object(material_type material, vector3 center) {
  geometric_object o;
  material_type_copy(&material, &o.material);
  o.center = center;
  o.which_subclass = GEOM GEOMETRIC_OBJECT_SELF;
  return o;
}

geometric_object make_cylinder(material_type material, vector3 center, number radius, number height,
                               vector3 axis) {
  geometric_object o = make_geometric_object(material, center);
  o.which_subclass = GEOM CYLINDER;
  o.subclass.cylinder_data = MALLOC1(cylinder);
  CHECK(o.subclass.cylinder_data, "out of memory");
  o.subclass.cylinder_data->radius = radius;
  o.subclass.cylinder_data->height = height;
  o.subclass.cylinder_data->axis = axis;
  o.subclass.cylinder_data->which_subclass = CYL CYLINDER_SELF;
  geom_fix_object_ptr(&o);
  return o;
}

geometric_object make_cone(material_type material, vector3 center, number radius, number height,
                           vector3 axis, number radius2) {
  geometric_object o = make_cylinder(material, center, radius, height, axis);
  o.subclass.cylinder_data->which_subclass = CYL CONE;
  o.subclass.cylinder_data->subclass.cone_data = MALLOC1(cone);
  CHECK(o.subclass.cylinder_data->subclass.cone_data, "out of memory");
  o.subclass.cylinder_data->subclass.cone_data->radius2 = radius2;
  return o;
}

geometric_object make_wedge(material_type material, vector3 center, number radius, number height,
                            vector3 axis, number wedge_angle, vector3 wedge_start) {
  geometric_object o = make_cylinder(material, center, radius, height, axis);
  o.subclass.cylinder_data->which_subclass = CYL WEDGE;
  o.subclass.cylinder_data->subclass.wedge_data = MALLOC1(wedge);
  CHECK(o.subclass.cylinder_data->subclass.wedge_data, "out of memory");
  o.subclass.cylinder_data->subclass.wedge_data->wedge_angle = wedge_angle;
  o.subclass.cylinder_data->subclass.wedge_data->wedge_start = wedge_start;
  geom_fix_object_ptr(&o);
  return o;
}

geometric_object make_sphere(material_type material, vector3 center, number radius) {
  geometric_object o = make_geometric_object(material, center);
  o.which_subclass = GEOM SPHERE;
  o.subclass.sphere_data = MALLOC1(sphere);
  CHECK(o.subclass.sphere_data, "out of memory");
  o.subclass.sphere_data->radius = radius;
  return o;
}

geometric_object make_block(material_type material, vector3 center, vector3 e1, vector3 e2,
                            vector3 e3, vector3 size) {
  geometric_object o = make_geometric_object(material, center);
  o.which_subclass = GEOM BLOCK;
  o.subclass.block_data = MALLOC1(block);
  CHECK(o.subclass.block_data, "out of memory");
  o.subclass.block_data->e1 = e1;
  o.subclass.block_data->e2 = e2;
  o.subclass.block_data->e3 = e3;
  o.subclass.block_data->size = size;
  o.subclass.block_data->which_subclass = BLK BLOCK_SELF;
  geom_fix_object_ptr(&o);
  return o;
}

geometric_object make_ellipsoid(material_type material, vector3 center, vector3 e1, vector3 e2,
                                vector3 e3, vector3 size) {
  geometric_object o = make_block(material, center, e1, e2, e3, size);
  o.subclass.block_data->which_subclass = BLK ELLIPSOID;
  o.subclass.block_data->subclass.ellipsoid_data = MALLOC1(ellipsoid);
  CHECK(o.subclass.block_data->subclass.ellipsoid_data, "out of memory");
  o.subclass.block_data->subclass.ellipsoid_data->inverse_semi_axes.x = 2.0 / size.x;
  o.subclass.block_data->subclass.ellipsoid_data->inverse_semi_axes.y = 2.0 / size.y;
  o.subclass.block_data->subclass.ellipsoid_data->inverse_semi_axes.z = 2.0 / size.z;
  return o;
}

/***************************************************************
 * The remainder of this file implements geometric primitives for prisms.
 * A prism is a planar polygon, consisting of 3 or more user-specified
 * vertices (the "bottom_vertices), extruded through a given thickness
 * (the "height") in the direction of a given unit vector (the "axis")
 * with the walls of the extrusion tapering at a given angle angle
 * (the "sidewall_angle).
 * Most calculations are done in the "prism coordinate system",
 * in which the prism floor lies in the XY plane with centroid
 * at the origin and the prism axis is the positive Z-axis.
 * Some variable naming conventions:
 *  -- Suffix 'p' or '_p' on variable names identifies variables
 *     storing coordinates or vector components in the prism system.
 *     Suffix 'c' or '_c' (or no suffix) corresponds to coodinates/components
 *     in ordinary 3d space. ('c' stands for 'cartesian').
 *  -- We use the term 'vertex' for points in 3-space, stored as vector3
 *     quantities with variable names beginning with 'p' or 'v'. For 3D
 *     direction vectors we use variable names beginning with 'd'.
 *  -- We use the term 'node' for points in 2-space, stored as vector3
 *     quantities (with the z component unused) with variables beginning with 'q'.
 *     For 2D direction vectors we use variable names beginning with 'u'.
 * homer reid 4/2018
 ***************************************************************/

/***************************************************************/
/* given coordinates of a point in the prism coordinate system,*/
/* return cartesian coordinates of that point                  */
/***************************************************************/
vector3 prism_coordinate_p2c(prism *prsm, vector3 pp) {
  return vector3_plus(prsm->centroid, matrix3x3_vector3_mult(prsm->m_p2c, pp));
}

vector3 prism_vector_p2c(prism *prsm, vector3 vp) {
  return matrix3x3_vector3_mult(prsm->m_p2c, vp);
}

vector3 prism_coordinate_c2p(prism *prsm, vector3 pc) {
  return matrix3x3_vector3_mult(prsm->m_c2p, vector3_minus(pc, prsm->centroid));
}

vector3 prism_vector_c2p(prism *prsm, vector3 vc) {
  return matrix3x3_vector3_mult(prsm->m_c2p, vc);
}

/***************************************************************/
/* given 2D points q0,q1,q2 and a 2D vector u, determine       */
/* whether or not the line q0 + s*u intersects the line        */
/* segment q1--q2.                                             */
/* algorithm: solve the 2x2 linear system q0+s*u = q1+t*(q2-q1)*/
/* for the scalar quantities s, t; intersection corresponds to */
/* 0 <= t < 1.                                                 */
/* return values:                                              */
/*  ** case 1: u is not parallel to q1--q2 **                  */
/*  NON_INTERSECTING: test negative                            */
/*      INTERSECTING: test positive                            */
/*  ** case 2: u is parallel to q1--q2 **                      */
/*  IN_SEGMENT:       q0 lies on line segment q1--q2           */
/*  ON_RAY:           q0 does not lie on q1--q2, but there is a*/
/*                    *positive* value of s such that q0+s*u   */
/*                    lies on q1--q2                           */
/* NON_INTERSECTING  neither of the above                      */
/***************************************************************/
#define THRESH 1.0e-5
#define NON_INTERSECTING 0
#define INTERSECTING 1
#define IN_SEGMENT 2
#define ON_RAY 3
int intersect_line_with_segment(vector3 q0, vector3 q1, vector3 q2, vector3 u, double *s) {
  /* ||ux   q1x-q2x|| |s| = | q1x-q0x | */
  /* ||uy   q1y-q2y|| |t| = | q1y-q0y | */
  double M00 = u.x, M01 = q1.x - q2.x;
  double M10 = u.y, M11 = q1.y - q2.y;
  double RHSx = q1.x - q0.x;
  double RHSy = q1.y - q0.y;
  double DetM = M00 * M11 - M01 * M10;
  double L2 = M01 * M01 + M11 * M11; // squared length of edge, used to set length scale
  if (fabs(DetM) < 1.0e-10 * L2) {   // d zero or nearly parallel to edge
    if (vector3_nearly_equal(q0, q1, 1e-12) || vector3_nearly_equal(q0, q2, 1e-12)) return IN_SEGMENT;
    double q01x = q0.x - q1.x, q01y = q0.y - q1.y, q01 = sqrt(q01x * q01x + q01y * q01y);
    double q02x = q0.x - q2.x, q02y = q0.y - q2.y, q02 = sqrt(q02x * q02x + q02y * q02y);
    double dot = q01x * q02x + q01y * q02y;
    if (fabs(dot) < (1.0 - THRESH) * q01 * q02)
      return NON_INTERSECTING;
    else if (dot < 0.0) {
      if (s) *s = 0.0;
      return IN_SEGMENT;
    }
    else if ((u.x * q01x + u.y * q01y) < 0.0) {
      if (s) *s = fmin(q01, q02) / sqrt(u.x * u.x + u.y * u.y);
      return ON_RAY;
    }
    return NON_INTERSECTING;
  }

  float t = (M00 * RHSy - M10 * RHSx) / DetM;
  if (s) *s = (M11 * RHSx - M01 * RHSy) / DetM;

  // the plumb line intersects the segment if 0<=t<=1, with t==0,1
  // corresponding to the endpoints; for our purposes we count
  // the intersection if the plumb line runs through the t==0 vertex, but
  // NOT the t==1 vertex, to avoid double-counting for complete polygons.
  return (t < -THRESH || t >= (1 - THRESH)) ? NON_INTERSECTING : INTERSECTING;
}

// like the previous routine, but only count intersections if s>=0
boolean intersect_ray_with_segment(vector3 q0, vector3 q1, vector3 q2, vector3 u, double *s) {
  double ss;
  int status = intersect_line_with_segment(q0, q1, q2, u, &ss);
  if (status == INTERSECTING && ss < 0.0) return NON_INTERSECTING;
  if (s) *s = ss;
  return status;
}

/***************************************************************/
/* 2D point-in-polygon test: return 1 if q0 lies within the    */
/* polygon with the given vertices, 0 otherwise.               */
// method: cast a plumb line in the positive x direction from  */
/* q0 to infinity and count the number of edges intersected;   */
/* point lies in polygon iff this is number is odd.            */
/***************************************************************/
/* Implementation of: */
/*															   */
/* M. Galetzka and P. Glauner, "A Simple and Correct Even-Odd  */
/* Algorithm for the Point-in-Polygon Problem for Complex      */
/* Polygons", Proceedings of the 12th International Joint      */
/* Conference on Computer Vision, Imaging and Computer         */
/* Graphics Theory and Applications (VISIGRAPP 2017), Volume   */
/* 1: GRAPP, Porto, Portugal, 2017.							   */
/***************************************************************/

boolean node_in_or_on_polygon(vector3 q0, vector3 *nodes, int num_nodes,
                              boolean include_boundaries) {
  // Create axes
  vector3 xAxis = {1.0, 0.0, 0.0};

  // Initial start point
  vector3 startPoint;
  vector3 endPoint;

  int startNodePosition = -1;
  int nn, edges_crossed = 0;

  // Is q0 on a vertex or edge?
  // Transform coordinate system of nodes such that q0 is at 0|0
  for (nn = 0; nn < num_nodes; nn++) {
    int status = intersect_ray_with_segment(q0, nodes[nn], nodes[(nn + 1) % num_nodes], unit_vector3(vector3_minus(nodes[(nn + 1) % num_nodes], nodes[nn])), 0);
    if (status == IN_SEGMENT) { return include_boundaries; }

    // Find start point which is not on the x axis (from q0)
    if (fabs(nodes[nn].y - q0.y) > THRESH) {
      startNodePosition = nn;
      startPoint = nodes[startNodePosition];
    }
  }

  // No start point found and point is not on an edge or node
  // --> point is outside
  if (startNodePosition == -1) { return 0; }

  int checkedPoints = 0;
  nn = startNodePosition;

  // Consider all edges
  while (checkedPoints < num_nodes) {
    int savedIndex = (nn + 1) % num_nodes;
    double savedX = nodes[savedIndex].x;

    // Move to next point which is not on the x-axis
    do {
      nn = (nn + 1) % num_nodes;
      checkedPoints++;
    } while (fabs(nodes[nn].y - q0.y) < THRESH);
    // Found end point
    endPoint = nodes[nn];

    // Only intersect lines that cross the x-axis (don't need to correct for rounding
    // error in the if statement because startPoint and endPoint are screened to
    // never lie on the x-axis)
    if ((startPoint.y - q0.y) * (endPoint.y - q0.y) < 0) {
      // No nodes have been skipped and the successor node
      // has been chose as the end point
      if (savedIndex == nn) {
        int status = intersect_ray_with_segment(q0, startPoint, endPoint, xAxis, 0);
        if (status == INTERSECTING) { edges_crossed++; }
      }
      // If at least one node on the right side has been skipped,
      // the original edge would have been intersected
      // --> intersect with full x-axis
      else if (savedX > q0.x + THRESH) {
        int status = intersect_line_with_segment(q0, startPoint, endPoint, xAxis, 0);
        if (status == INTERSECTING) { edges_crossed++; }
      }
    }
    // End point is the next start point
    startPoint = endPoint;
  }

  // Odd count --> in the polygon (1)
  // Even count --> outside (0)
  return edges_crossed % 2;
}

boolean node_in_polygon(double q0x, double q0y, vector3 *nodes, int num_nodes) {
  vector3 q0;
  q0.x = q0x;
  q0.y = q0y;
  q0.z = 0.0;
  return node_in_or_on_polygon(q0, nodes, num_nodes, 1);
}

/***************************************************************/
/* return 1 or 0 if pc lies inside or outside the prism        */
/***************************************************************/
boolean point_in_or_on_prism(prism *prsm, vector3 pc, boolean include_boundaries) {
  double height = prsm->height;
  vector3 pp = prism_coordinate_c2p(prsm, pc);
  if (pp.z < 0.0 || pp.z > prsm->height) return 0;
  int num_nodes = prsm->vertices_p.num_items;
  vector3 nodes[num_nodes];
  int nv;
  for (nv = 0; nv < num_nodes; nv++) {
    nodes[nv] = vector3_plus(prsm->vertices_p.items[nv], vector3_scale(pp.z, prsm->top_polygon_diff_vectors_scaled_p.items[nv]));
  }
  return node_in_or_on_polygon(pp, nodes, num_nodes, include_boundaries);
}

boolean point_in_prism(prism *prsm, vector3 pc) {
  // by default, points on polygon edges are considered to lie inside the
  // polygon; this can be reversed by setting the environment variable
  // LIBCTL_EXCLUDE_BOUNDARIES=1
  static boolean include_boundaries = 1, init = 0;
  if (init == 0) {
    init = 1;
    char *s = getenv("LIBCTL_EXCLUDE_BOUNDARIES");
    if (s && s[0] == '1') include_boundaries = 0;
  }
  return point_in_or_on_prism(prsm, pc, include_boundaries);
}

// comparator for qsort
static int dcmp(const void *pd1, const void *pd2) {
  double d1 = *((double *)pd1), d2 = *((double *)pd2);
  return (d1 < d2) ? -1.0 : (d1 > d2) ? 1.0 : 0.0;
}

/******************************************************************/
/* 3D line-prism intersection: compute all values of s at which   */
/* the line p+s*d intersects a prism face.                        */
/* pc, dc = cartesian coordinates of p, cartesian components of d */
/* slist is a caller-allocated buffer with enough room for        */
/* at least num_vertices+2 doubles. on return it contains         */
/* the intersection s-values sorted in ascending order.           */
/* the return value is the number of intersections.               */
/******************************************************************/
int intersect_line_with_prism(prism *prsm, vector3 pc, vector3 dc, double *slist) {
  vector3 pp = prism_coordinate_c2p(prsm, pc);
  vector3 dp = prism_vector_c2p(prsm, dc);
  vector3 *vps_bottom = prsm->vertices_p.items;
  vector3 *vps_top = prsm->vertices_top_p.items;
  int num_vertices = prsm->vertices_p.num_items;
  double height = prsm->height;

  // identify intersections with prism side faces
  double tus_tolerance = 1e-8;
  int num_intersections = 0;
  int nv;
  for (nv = 0; nv < num_vertices; nv++) {
    int nvp1 = nv + 1;
    if (nvp1 == num_vertices) nvp1 = 0;

    // checks if dp is parallel to the plane of the prism side face under consideration
    vector3 v1 = vector3_minus(vps_bottom[nvp1], vps_bottom[nv]);
    vector3 v2 = vector3_minus(vps_top[nv], vps_bottom[nv]);
    double dot_tolerance = 1e-6;
    if (fabs(vector3_dot(dp, vector3_cross(v1, v2))) <= dot_tolerance) continue;

    // to find the intersection point pp + s*dp between the line and the
    // prism side face, we will solve the vector equation
    //             pp + s*dp = o + t*v1 + u*v2
    // where o is vps_bottom[nv], v1 is vps_bottom[nvp1]-vps_bottom[nv],
    // v2 is vps_top[nv]-vps_bottom[nv], and 0 <= t <= 1, 0 <= u <= 1.
    matrix3x3 M;
    M.c0 = v1;
    M.c1 = v2;
    M.c2 = vector3_scale(-1, dp);
    vector3 RHS = vector3_minus(pp, vps_bottom[nv]);
    vector3 tus = matrix3x3_vector3_mult(matrix3x3_inverse(M), RHS);
    if (tus.x < -tus_tolerance || tus.x > 1+tus_tolerance || tus.y < -tus_tolerance || tus.y > 1+tus_tolerance) continue;
    double s = tus.z;
    slist[num_intersections++] = s;
  }

  // identify intersections with prism ceiling and floor faces
  int LowerUpper;
  if (fabs(dp.z) > 1.0e-7 * vector3_norm(dp))
    for (LowerUpper = 0; LowerUpper < 2; LowerUpper++) {
      double z0p = LowerUpper ? height : 0.0;
      double s = (z0p - pp.z) / dp.z;
      vector3 *vps = LowerUpper ? vps_top : vps_bottom;
      if (!node_in_polygon(pp.x + s * dp.x, pp.y + s * dp.y, vps, num_vertices)) continue;
      slist[num_intersections++] = s;
    }

  qsort((void *)slist, num_intersections, sizeof(double), dcmp);
  // if num_intersections is zero then just return that
  if (num_intersections == 0) return num_intersections;
  else {
    // remove duplicates from slist
    double duplicate_tolerance = 1e-3;
    int num_unique_elements = 1;
    double slist_unique[num_vertices+2];
    slist_unique[0] = slist[0];
    for (nv = 1; nv < num_intersections; nv++) {
      if (fabs(slist[nv] - slist[nv-1]) > duplicate_tolerance*fabs(slist[nv])) {
        slist_unique[num_unique_elements] = slist[nv];
        num_unique_elements++;
      }
    }
    slist = slist_unique;
    num_intersections = num_unique_elements;
    return num_intersections;
  }
}

/***************************************************************/
/***************************************************************/
/***************************************************************/
double intersect_line_segment_with_prism(prism *prsm, vector3 pc, vector3 dc, double a, double b) {
  double *slist = prsm->workspace.items;
  int num_intersections = intersect_line_with_prism(prsm, pc, dc, slist);

  // na=smallest index such that slist[na] > a
  int na = -1;
  int ns;
  for (ns = 0; na == -1 && ns < num_intersections; ns++)
    if (slist[ns] > a) na = ns;

  if (na == -1) return 0.0;

  int inside = ((na % 2) == 0 ? 0 : 1);
  double last_s = a;
  double ds = 0.0;
  for (ns = na; ns < num_intersections; ns++) {
    double this_s = fmin(b, slist[ns]);
    if (inside) ds += (this_s - last_s);
    if (b < slist[ns]) break;
    inside = (1 - inside);
    last_s = this_s;
  }
  return ds > 0.0 ? ds : 0.0;
}

/***************************************************************/
/* compute the minimum distance from a 3D point p to the       */
/* line segment with endpoints v1,v2.                          */
/* algorithm: let pLine = v1 + d*(v2-v1) be the point on the   */
/* line closest to p; d is defined by minimizing |p-pLine|^2.  */
/* --> |p-v1|^2 + d^2 |v2-v1|^2 - 2*d*dot(p-v1,v2-v1) = min    */
/* -->            2d  |v2-v1|^2 -   2*dot(p-v1,v2-v1) = 0      */
/* --> d = dot(p-v1,v2-v1) / |v2-v1|^2                         */
/***************************************************************/
double min_distance_to_line_segment(vector3 p, vector3 v1, vector3 v2) {
  vector3 v2mv1 = vector3_minus(v2, v1);
  vector3 pmv1 = vector3_minus(p, v1);
  double d = vector3_dot(v2mv1, pmv1) / vector3_dot(v2mv1, v2mv1);
  if (d < 0.0) d = 0.0; // if pProj lies outside the line segment,
  if (d > 1.0) d = 1.0; //  displace it to whichever vertex is closer
  vector3 pLine = vector3_plus(v1, vector3_scale(d, v2mv1));
  return vector3_norm(vector3_minus(p, pLine));
}

/***************************************************************/
/* compute the projection of a 3D point p into the plane       */
/* that contains the three points {o, o+v1, o+v2} and has      */
/* normal vector v3.                                           */
/* algorithm: solve a 3x3 system to compute the projection of  */
/*            p into the plane (call it pPlane)                */
/*                pPlane = p-s*v3 = o + t*v1 + u*v2            */
/*            where v3 is the normal to the plane and s,t,u    */
/*            are unknowns.                                    */
/* the return value is the value of s (where pPlane = p-s*v3), */
/* i.e. the minimum distance from p to the plane.              */
/* if in_quadrilateral is non-null it is set to 0              */
/* or 1 according as pPlane does or does not lie in the        */
/* quadrilateral with vertices (o, o+v1, o+v2, o+v1+v2).       */
/***************************************************************/
double normal_distance_to_plane(vector3 p, vector3 o, vector3 v1, vector3 v2, vector3 v3,
                                int *in_quadrilateral) {
  CHECK((vector3_norm(v3) > 1.0e-6), "degenerate plane in project_point_into_plane");
  matrix3x3 M;
  M.c0 = v1;
  M.c1 = v2;
  M.c2 = v3;
  vector3 RHS = vector3_minus(p, o);
  vector3 tus = matrix3x3_vector3_mult(matrix3x3_inverse(M), RHS); // "t, u, s"
  float t = tus.x, u = tus.y, s = tus.z;
  if (in_quadrilateral)
    *in_quadrilateral = ((0.0 <= t && t <= 1.0 && 0.0 <= u && u <= 1.0) ? 1 : 0);
  return s;
}

// like normal_distance_to_plane, but if pPlane (projection of point into plane)
// lies outside the quadrilateral {o,o+v1,o+v2,o+v1+v2} then take into account
// the in-plane distance from pPlane to the quadrilateral
double min_distance_to_quadrilateral(vector3 p, vector3 o, vector3 v1, vector3 v2, vector3 v3) {
  int inside;
  double s = normal_distance_to_plane(p, o, v1, v2, v3, &inside);
  if (inside == 1) return s;
  vector3 pPlane = vector3_minus(p, vector3_scale(s, v3));
  vector3 p01 = vector3_plus(o, v1);
  vector3 p10 = vector3_plus(o, v2);
  vector3 p11 = vector3_plus(p01, v2);
  double d = min_distance_to_line_segment(pPlane, o, p01);
  d = fmin(d, min_distance_to_line_segment(pPlane, o, p10));
  d = fmin(d, min_distance_to_line_segment(pPlane, p01, p11));
  d = fmin(d, min_distance_to_line_segment(pPlane, p11, p10));
  return sqrt(s * s + d * d);
}

// fc==0/1 for floor/ceiling
double min_distance_to_prism_roof_or_ceiling(vector3 pp, prism *prsm, int fc) {
  int num_vertices = prsm->vertices_p.num_items, i;
  vector3 op = {0.0, 0.0, 0.0}; // origin of floor/ceiling
  vector3 vps[num_vertices];
  if (fc == 1) {
    memcpy(vps, prsm->vertices_top_p.items, num_vertices * sizeof(vector3));
    for (i = 0; i < num_vertices; i++) {
      vps[i].z = 0;
    }
    op.z = prsm->height;
  }
  else {
    memcpy(vps, prsm->vertices_p.items, num_vertices * sizeof(vector3));
  }
  vector3 zhatp = {0, 0, 1.0};
  double s = normal_distance_to_plane(pp, op, vps[0], vps[1], zhatp, 0);
  vector3 ppProj =
      vector3_minus(pp, vector3_scale(s, zhatp)); // projection of p into plane of floor/ceiling
  if (node_in_polygon(ppProj.x, ppProj.y, vps, num_vertices) == 1) return s;

  int nv;
  double d = min_distance_to_line_segment(ppProj, vps[0], vps[1]);
  for (nv = 1; nv < num_vertices; nv++)
    d = fmin(d, min_distance_to_line_segment(ppProj, vps[nv], vps[(nv + 1) % num_vertices]));
  return sqrt(s * s + d * d);
}

/***************************************************************/
/* find the face of the prism for which the normal distance    */
/* from p to the plane of that face is the shortest, then      */
/* return the normal vector to that plane.                     */
/***************************************************************/
vector3 normal_to_prism(prism *prsm, vector3 pc) {
  if (prsm->height == 0.0) return prsm->axis;

  double height = prsm->height;
  vector3 *vps_bottom = prsm->vertices_p.items;
  vector3 *vps_diff_to_top = prsm->top_polygon_diff_vectors_p.items;
  int num_vertices = prsm->vertices_p.num_items;

  vector3 zhatp = {0.0, 0.0, 1.0};
  vector3 axisp = vector3_scale(height, zhatp);
  vector3 pp = prism_coordinate_c2p(prsm, pc);

  vector3 retval;
  double min_distance = HUGE_VAL;
  int nv;
  // consider side walls
  for (nv = 0; nv < num_vertices; nv++) {
    int nvp1 = (nv == (num_vertices - 1) ? 0 : nv + 1);
    vector3 v0p = vps_bottom[nv];
    vector3 v1p = vector3_minus(vps_bottom[nvp1], vps_bottom[nv]);
    vector3 v2p = vps_diff_to_top[nv];
    vector3 v3p = unit_vector3(vector3_cross(v1p, v2p));
    double s = min_distance_to_quadrilateral(pp, v0p, v1p, v2p, v3p);
    if (fabs(s) < min_distance) {
      min_distance = fabs(s);
      retval = v3p;
    }
  }

  int fc; // 'floor / ceiling'
  for (fc = 0; fc < 2; fc++) {
    double s = min_distance_to_prism_roof_or_ceiling(pp, prsm, fc);
    if (fabs(s) < min_distance) {
      min_distance = fabs(s);
      retval = zhatp;
    }
  }
  return prism_vector_p2c(prsm, retval);
}

/***************************************************************/
/* Compute the area of a polygon using its vertices.           */
/***************************************************************/
double get_area_of_polygon_from_nodes(vector3 *nodes, int num_nodes){
  double area = 0;
  int i;
  for (i = 0; i < num_nodes; ++i) {
    int i1 = (i + 1) % num_nodes;
    area += 0.5 * (nodes[i1].x - nodes[i].x) *
            (nodes[i1].y + nodes[i].y);
  }
  return fabs(area);
}

/***************************************************************/
/* This computes the volume of an irregular triangular prism   */
/* following the scheme of http://darrenirvine.blogspot.com/2011/10/volume-of-irregular-triangular-prism.html */
/* The two end triangles have points a, b, and c. Angle abc    */
/* is right, and angles bac and acb are acute, of course. The  */
/* primary constraint for this method is that the lines be-    */
/* tween 'a's between triangles, betweens 'b's between         */
/* triangles, and between 'c's between triangles must all be   */
/* parallel, though the end triangles need not be parallel.    */

/***************************************************************/
double get_volume_irregular_triangular_prism(vector3 a0, vector3 b0, vector3 c0, vector3 a1, vector3 b1, vector3 c1) {
  vector3 side_a = vector3_minus(a1, a0);
  vector3 side_b = vector3_minus(b1, b0);
  vector3 side_c = vector3_minus(c1, c0);
  if (vector3_norm(vector3_cross(side_a, side_b)) != 0 ||
      vector3_norm(vector3_cross(side_b, side_c)) != 0 ||
      vector3_norm(vector3_cross(side_c, side_a)) != 0) {
    //throw an error
  }
  double length_side_a = vector3_norm(side_a);
  double length_side_b = vector3_norm(side_b);
  double length_side_c = vector3_norm(side_c);
  double average_length = (length_side_a + length_side_b + length_side_c) / 3.0;

  vector3 point_on_plane = a0;
  vector3 plane_normal_vector = unit_vector3(side_a);
  vector3 plane_to_a1 = vector3_minus(a1, point_on_plane);
  vector3 plane_to_b1 = vector3_minus(b1, point_on_plane);
  vector3 plane_to_c1 = vector3_minus(c1, point_on_plane);
  vector3 proj_plane_to_a1_on_normal_vector = vector3_scale(vector3_dot(plane_normal_vector, plane_to_a1), plane_normal_vector);
  vector3 proj_plane_to_b1_on_normal_vector = vector3_scale(vector3_dot(plane_normal_vector, plane_to_b1), plane_normal_vector);
  vector3 proj_plane_to_c1_on_normal_vector = vector3_scale(vector3_dot(plane_normal_vector, plane_to_c1), plane_normal_vector);
  vector3 a1_on_plane = vector3_minus(a1, proj_plane_to_a1_on_normal_vector);
  vector3 b1_on_plane = vector3_minus(b1, proj_plane_to_b1_on_normal_vector);
  vector3 c1_on_plane = vector3_minus(c1, proj_plane_to_c1_on_normal_vector);
  double base = vector3_norm(vector3_minus(c1_on_plane, b1_on_plane));
  double height = vector3_norm(vector3_minus(a1_on_plane, b1_on_plane));
  double cross_sectional_area = fabs(0.5 * base * height);

  return fabs(average_length * cross_sectional_area);
}

/***************************************************************/
/***************************************************************/
/***************************************************************/
double get_prism_volume(prism *prsm) {
  if (prsm->sidewall_angle == 0.0) {
    return get_area_of_polygon_from_nodes(prsm->vertices_p.items, prsm->vertices_p.num_items) * fabs(prsm->height);
  }
  else {
    int num_vertices = prsm->vertices_p.num_items, nv;
    double bottom_polygon_area = get_area_of_polygon_from_nodes(prsm->vertices_p.items, prsm->vertices_p.num_items);
    double top_polygon_area = get_area_of_polygon_from_nodes(prsm->vertices_top_p.items, prsm->vertices_top_p.num_items);
    double volume;
    vector3 *wedges_a;
    wedges_a = (vector3 *)malloc(num_vertices * sizeof(vector3));
    CHECK(wedges_a, "out of memory");
    vector3 *wedges_b;
    wedges_b = (vector3 *)malloc(num_vertices * sizeof(vector3));
    CHECK(wedges_b, "out of memory");
    vector3 *wedges_c;
    wedges_c = (vector3 *)malloc(num_vertices * sizeof(vector3));
    CHECK(wedges_c, "out of memory");
    if (bottom_polygon_area > top_polygon_area) {
      volume = fabs(top_polygon_area * prsm->height);
      memcpy(wedges_a, prsm->vertices_top_p.items, num_vertices * sizeof(vector3));
      memcpy(wedges_b, prsm->vertices_top_p.items, num_vertices * sizeof(vector3));
      for (nv = 0; nv < num_vertices; nv++) {
        wedges_b[nv].z = 0.0;
      }
      memcpy(wedges_c, prsm->vertices_p.items, num_vertices * sizeof(vector3));
    }
    else {
      volume = fabs(bottom_polygon_area * prsm->height);
      memcpy(wedges_a, prsm->vertices_p.items, num_vertices * sizeof(vector3));
      memcpy(wedges_b, prsm->vertices_p.items, num_vertices * sizeof(vector3));
      for (nv = 0; nv < num_vertices; nv++) {
        wedges_b[nv].z = prsm->height;
      }
      memcpy(wedges_c, prsm->vertices_top_p.items, num_vertices * sizeof(vector3));
    }
    for (nv = 0; nv < num_vertices; nv++) {
      int nvp1 = (nv + 1 == num_vertices ? 0 : nv + 1);
      volume += get_volume_irregular_triangular_prism(wedges_a[nv], wedges_b[nv], wedges_c[nv], wedges_a[nvp1], wedges_b[nvp1], wedges_c[nvp1]);
    }
    return volume;
  }
}

/***************************************************************/
/***************************************************************/
/***************************************************************/
void get_prism_bounding_box(prism *prsm, geom_box *box) {
  vector3 *vertices = prsm->vertices.items;
  vector3 *vertices_top = prsm->vertices_top.items;
  int num_vertices = prsm->vertices.num_items;
  box->low = box->high = vertices[0];
  int nv, fc;
  for (nv = 0; nv < num_vertices; nv++)
    for (fc = 0; fc < 2; fc++) // 'floor,ceiling'
    {
      vector3 v;
      if (fc == 0) v = vertices[nv];
      if (fc == 1) v = vertices_top[nv];

      box->low.x = fmin(box->low.x, v.x);
      box->low.y = fmin(box->low.y, v.y);
      box->low.z = fmin(box->low.z, v.z);

      box->high.x = fmax(box->high.x, v.x);
      box->high.y = fmax(box->high.y, v.y);
      box->high.z = fmax(box->high.z, v.z);
    }
}

/***************************************************************/
/***************************************************************/
/***************************************************************/
void display_prism_info(int indentby, geometric_object *o) {
  prism *prsm = o->subclass.prism_data;

  vector3 *vs = prsm->vertices.items;
  int num_vertices = prsm->vertices.num_items;

  ctl_printf("%*s     height %g, axis (%g,%g,%g), sidewall angle: %g radians, %i vertices:\n", indentby, "", prsm->height,
             prsm->axis.x, prsm->axis.y, prsm->axis.z, prsm->sidewall_angle, num_vertices);
  int nv;
  for (nv = 0; nv < num_vertices; nv++)
    ctl_printf("%*s     (%g,%g,%g)\n", indentby, "", vs[nv].x, vs[nv].y, vs[nv].z);
}

/***************************************************************/
// like vector3_equal but tolerant of small floating-point discrepancies
/***************************************************************/
int vector3_nearly_equal(vector3 v1, vector3 v2, double tolerance) {
  return (vector3_norm(vector3_minus(v1, v2)) <= tolerance * vector3_norm(v1));
}
matrix3x3 sidewall_scaling_matrix;

/***************************************************************/
/* return the unit normal vector to the triangle with the given*/
/* vertices                                                    */
/***************************************************************/
vector3 triangle_normal(vector3 v1, vector3 v2, vector3 v3) {
  vector3 nv = vector3_cross(vector3_minus(v2, v1), vector3_minus(v3, v1));
  double nvnorm = vector3_norm(nv);
  // if (area) *area += 0.5*nvnorm;
  return unit_vector3(nv);
}

/***************************************************************/
/* On entry, the only fields in o->prism that are assumed to   */
/* be initialized are: vertices, height, (optionally)          */
/* axis, and sidewall_angle. If axis has not been initialized  */
/* (i.e. it is set to its default value, which is the zero     */
/* vector) then the prism axis is automatically computed as    */
/* the normal to the vertex plane. If o->center is equal to    */
/* auto_center on entry, then it is set to the prism center,   */
/* as computed from the vertices, axis, and height. Otherwise, */
/* the prism is rigidly translated to center it at the         */
/* specified value of o->center.                               */
/***************************************************************/
// special vector3 that signifies 'no value specified'
vector3 auto_center = {NAN, NAN, NAN};
void init_prism(geometric_object *o) {
  prism *prsm = o->subclass.prism_data;
  vector3 *vertices = prsm->vertices.items;
  int num_vertices = prsm->vertices.num_items;
  CHECK(num_vertices >= 3, "fewer than 3 vertices in init_prism");

  // remove duplicate consecutive prism vertices
  int i = 0; // last non-deleted vertex
  for (int j = 1; j < num_vertices; ++j) {
    if (!vector3_equal(vertices[i], vertices[j])) {
      i += 1;
      if (i < j) vertices[i] = vertices[j];
    }
  }
  num_vertices = i + 1 - vector3_equal(vertices[0], vertices[i]);
  CHECK(num_vertices >= 3, "fewer than 3 non-duplicate vertices in init_prism");
  if (prsm->vertices.num_items < num_vertices) {
    prsm->vertices.num_items = num_vertices;
    vertices = (vector3 *)realloc(vertices, num_vertices * sizeof(vector3));
  }

  // compute centroid of vertices
  vector3 centroid = {0.0, 0.0, 0.0};
  int nv;
  for (nv = 0; nv < num_vertices; nv++)
    centroid = vector3_plus(centroid, vertices[nv]);
  prsm->centroid = centroid = vector3_scale(1.0 / ((double)num_vertices), centroid);

  // make sure all vertices lie in a plane, i.e. that the normal
  // vectors to all triangles (v_n, v_{n+1}, centroid) agree.
  int plane_normal_set = 0;
  vector3 plane_normal;
  double tol = 1.0e-6;
  for (nv = 0; nv < num_vertices; nv++) {
    int nvp1 = (nv + 1) % num_vertices;
    vector3 tri_normal = triangle_normal(centroid, vertices[nv], vertices[nvp1]);
    if (vector3_norm(tri_normal) == 0.0) // vertices collinear with centroid
      continue;
    if (!plane_normal_set) {
      plane_normal = tri_normal;
      plane_normal_set = 1;
    }
    else {
      boolean normals_agree =
          (vector3_nearly_equal(plane_normal, tri_normal, tol) ||
           vector3_nearly_equal(plane_normal, vector3_scale(-1.0, tri_normal), tol));
      CHECK(normals_agree, "non-coplanar vertices in init_prism");
    }
  }

  // if no prism axis was specified, set the prism axis equal to the
  // normal to the vertex plane.
  // if a prism axis was specified, check that it agrees up to sign
  // with the normal to the vertex plane.
  if (vector3_norm(prsm->axis) == 0.0)
    prsm->axis = plane_normal;
  else {
    prsm->axis = unit_vector3(prsm->axis);
    boolean axis_normal_to_plane =
        (vector3_nearly_equal(prsm->axis, plane_normal, tol) ||
         vector3_nearly_equal(prsm->axis, vector3_scale(-1.0, plane_normal), tol));
    CHECK(axis_normal_to_plane, "axis not normal to vertex plane in init_prism");
  }

  // set current_center=prism center as determined by vertices and height.
  // if the center of the geometric object was left unspecified,
  // set it to current_center; otherwise displace the entire prism
  // so that it is centered at the specified center.
  vector3 current_center = vector3_plus(centroid, vector3_scale(0.5 * prsm->height, prsm->axis));
  if (isnan(o->center.x) && isnan(o->center.y) && isnan(o->center.z)) // center == auto-center
    o->center = current_center;
  else {
    vector3 shift = vector3_minus(o->center, current_center);
    for (nv = 0; nv < num_vertices; nv++)
      vertices[nv] = vector3_plus(vertices[nv], shift);
    centroid = vector3_plus(centroid, shift);
  }

  // compute rotation matrix that operates on a vector of cartesian coordinates
  // to yield the coordinates of the same point in the prism coordinate system.
  // the prism coordinate system is a right-handed coordinate system
  // in which the prism lies in the xy plane (extrusion axis is the positive z-axis)
  // with centroid at the origin.
  // note: the prism *centroid* is the center of mass of the planar vertex polygon,
  //       i.e. it is a point lying on the bottom surface of the prism.
  //       This is the origin of coordinates in the prism system.
  //       The *center* of the geometric object is the center of mass of the
  //       3D prism. So center = centroid + 0.5*height*zHat.
  vector3 x0hat = {1.0, 0.0, 0.0}, y0hat = {0.0, 1.0, 0.0}, z0hat = {0.0, 0.0, 1.0};
  vector3 xhat, yhat, zhat = prsm->axis;
  if (vector3_nearly_equal(zhat, x0hat, tol)) {
    xhat = y0hat;
    yhat = z0hat;
  }
  else if (vector3_nearly_equal(zhat, y0hat, tol)) {
    xhat = z0hat;
    yhat = x0hat;
  }
  else if (vector3_nearly_equal(zhat, z0hat, tol)) {
    xhat = x0hat;
    yhat = y0hat;
  }
  else {
    xhat = unit_vector3(vector3_minus(vertices[1], vertices[0]));
    yhat = unit_vector3(vector3_cross(zhat, xhat));
  }
  matrix3x3 m_p2c = {xhat, yhat, zhat};
  prsm->m_p2c = m_p2c;
  prsm->m_c2p = matrix3x3_inverse(m_p2c);

  // compute vertices in prism coordinate system
  prsm->vertices_p.num_items = num_vertices;
  prsm->vertices_p.items = (vector3 *)malloc(num_vertices * sizeof(vector3));
  for (nv = 0; nv < num_vertices; nv++)
    prsm->vertices_p.items[nv] = prism_coordinate_c2p(prsm, vertices[nv]);

  // Calculate difference vertices of the top polygon and vectors between bottom
  // polygon and the top polygon, where:
  //  * the bottom polygon is the one passed in to the the make_prism() function,
  //    stored in vertices and vertices_p,
  //  * the top polygon is the top surface (parallel to the bottom polygon) resulting
  //    from the extrusion of the bottom polygon. Whether or not the extrusion tapers
  //    is dependent on the value of sidewall_angle.
  //
  // The top polygon is calculated by first copying the values of vertices_p into
  // vertices_top_p, except z=prsm->height for all top vertices. If prsm->sidewall_angle
  // is equal to zero, then no further calculations are performed on the top vertices.
  // If not, we know that all EDGES of the the top polygon will be offset so that in the
  // xy plane they are parallel to the edges of the bottom polygon. The offset amount is
  // determined by the sidewall angle and the height of the prism. To perform the
  // calculation, each of the edges of the top polygon (without an offset) are stored in
  // an array of edges (edge is a struct defined if prsm->sidewall_angle!=0 containing
  // the endpoints a1 a2, with a third vector v defined a2-a1). Then the vector normal to
  // v is calculated, and the offset vector. A test is performed to determine in which
  // direction (the direction of +offset or -offset) from the edge we can find points
  // inside the polygon by performing a node_in_or_on_polygon test at a finite distance
  // away from the midpoint of the edge:
  //          edge.a1 + 0.5*edge.v + 1e-3*offset.
  // This information is used to determine in which direction the offset of the edge is
  // applied, in conjunction with whether prsm->sidewall_angle is positive or negative
  // (if positive, the offset will be applied in towards the points where
  // node_in_or_on_polygon is true, else the offset will be applied out away from those
  // points). After the offsets are applied to the edges, the intersections between the
  // new edges are calculated, which are the new values of vertices_top_p.
  //
  // Some side notes on the difference vectors:
  //   * The value of each of the top polygon vertices can be found
  //             vertices_p + top_polygon_diff_vectors_p
  //             vertices   + top_polygon_diff_vectors
  //   * A linearly interpolated value of the polygon vertices between the bottom
  //     polygon and the top can be found
  //             vertices_p + top_polygon_diff_vectors_scaled_p * z
  number theta = (K_PI/2) - fabs(prsm->sidewall_angle);
  prsm->vertices_top_p.num_items = num_vertices;
  prsm->vertices_top_p.items = (vector3 *)malloc(num_vertices * sizeof(vector3));
  CHECK(prsm->vertices_top_p.items, "out of memory");
  memcpy(prsm->vertices_top_p.items, prsm->vertices_p.items, num_vertices * sizeof(vector3));
  for (nv = 0; nv < num_vertices; nv++) {
    prsm->vertices_top_p.items[nv].z = prsm->height;
  }

  if (prsm->sidewall_angle != 0.0) {
    typedef struct {
      vector3 a1, a2, v;  // v will be defined as a2 - a1
    } edge;

    // find the point at the bottom left corner of the polygon
    double smallest_x = HUGE_VAL;
    double smallest_y = HUGE_VAL;
    int index_for_point_a = -1;
    int index_for_point_b = -1;
    int index_for_point_c = -1;
    for (nv = 0; nv < num_vertices; nv++) {
        double current_x = prsm->vertices_p.items[nv].x;
        double current_y = prsm->vertices_p.items[nv].y;
        if (current_x < smallest_x) {
            smallest_x = current_x;
            smallest_y = current_y;
            index_for_point_b = nv;
        }
        else if (current_x == smallest_x && current_y < smallest_y) {
            smallest_y = current_y;
            index_for_point_b = nv;
        }
    }
    if (index_for_point_b == -1) {
        exit(EXIT_FAILURE);
    }
    else {
        index_for_point_a = (index_for_point_b + 1 == num_vertices ? 0 : index_for_point_b + 1);
        index_for_point_c = (index_for_point_b - 1 == -1 ? num_vertices - 1 : index_for_point_b - 1);
    }
    // find orientation of the polygon
    vector3 A = prsm->vertices_p.items[index_for_point_a];
    vector3 B = prsm->vertices_p.items[index_for_point_b];
    vector3 C = prsm->vertices_p.items[index_for_point_c];
    double orientation_number = (B.x - A.x)*(C.y - A.y)-(C.x - A.x)*(B.y - A.y);
    int orientation_positive_or_negative = (orientation_number < 0 ? 0 : 1);

    edge *top_polygon_edges;
    top_polygon_edges = (edge *)malloc(num_vertices * sizeof(edge));
    number w = prsm->height / tan(theta);

    for (nv = 0; nv < num_vertices; nv++) {
      top_polygon_edges[nv].a1 = prsm->vertices_top_p.items[(nv - 1 == -1 ? num_vertices - 1 : nv - 1)];
      top_polygon_edges[nv].a2 = prsm->vertices_top_p.items[nv];
      top_polygon_edges[nv].v = vector3_minus(top_polygon_edges[nv].a2, top_polygon_edges[nv].a1);

      vector3 normal_vector = (orientation_positive_or_negative ? unit_vector3(vector3_cross(top_polygon_edges[nv].v, zhat)) : unit_vector3(vector3_cross(top_polygon_edges[nv].v, vector3_scale(-1, zhat))));

      // positive sidewall angles means the prism tapers in towards the rest of the prism body
      // negative sidewall angles means the prism tapers out away from the rest of the prism body
      vector3 offset = vector3_scale(prsm->sidewall_angle > 0 ? w : -w, normal_vector);
      top_polygon_edges[nv].a1 = vector3_plus(top_polygon_edges[nv].a1, offset);
      top_polygon_edges[nv].a2 = vector3_plus(top_polygon_edges[nv].a2, offset);
    }

    for (nv = 0; nv < num_vertices; nv++) {
      number x1 = top_polygon_edges[nv].a1.x;
      number y1 = top_polygon_edges[nv].a1.y;
      number x2 = top_polygon_edges[nv].a2.x;
      number y2 = top_polygon_edges[nv].a2.y;
      number x3 = top_polygon_edges[(nv + 1 == num_vertices ? 0 : nv + 1)].a1.x;
      number y3 = top_polygon_edges[(nv + 1 == num_vertices ? 0 : nv + 1)].a1.y;
      number x4 = top_polygon_edges[(nv + 1 == num_vertices ? 0 : nv + 1)].a2.x;
      number y4 = top_polygon_edges[(nv + 1 == num_vertices ? 0 : nv + 1)].a2.y;

      // Intersection point calculated with https://en.wikipedia.org/wiki/Line%E2%80%93line_intersection#Given_two_points_on_each_line
      number px = ((x1*y2-y1*x2)*(x3-x4)-(x1-x2)*(x3*y4-y3*x4)) / ((x1-x2)*(y3-y4)-(y1-y2)*(x3-x4));
      number py = ((x1*y2-y1*x2)*(y3-y4)-(y1-y2)*(x3*y4-y3*x4)) / ((x1-x2)*(y3-y4)-(y1-y2)*(x3-x4));
      prsm->vertices_top_p.items[nv].x = px;
      prsm->vertices_top_p.items[nv].y = py;
    }
  }

  prsm->top_polygon_diff_vectors_p.num_items = num_vertices;
  prsm->top_polygon_diff_vectors_p.items = (vector3 *)malloc(num_vertices * sizeof(vector3));
  CHECK(prsm->top_polygon_diff_vectors_p.items, "out of memory");
  for (nv = 0; nv < num_vertices; nv++) {
    prsm->top_polygon_diff_vectors_p.items[nv] = vector3_minus(prsm->vertices_top_p.items[nv], prsm->vertices_p.items[nv]);
  }

  prsm->top_polygon_diff_vectors_scaled_p.num_items = num_vertices;
  prsm->top_polygon_diff_vectors_scaled_p.items = (vector3 *)malloc(num_vertices * sizeof(vector3));
  CHECK(prsm->top_polygon_diff_vectors_scaled_p.items, "out of memory");
  for (nv = 0; nv < num_vertices; nv++) {
      prsm->top_polygon_diff_vectors_scaled_p.items[nv] = vector3_scale(1/prsm->height, prsm->top_polygon_diff_vectors_p.items[nv]);
  }

  prsm->vertices_top.num_items = num_vertices;
  prsm->vertices_top.items = (vector3 *)malloc(num_vertices * sizeof(vector3));
  CHECK(prsm->vertices_top.items, "out of memory");
  for (nv = 0; nv < num_vertices; nv++) {
    prsm->vertices_top.items[nv] = prism_coordinate_p2c(prsm, prsm->vertices_top_p.items[nv]);
  }

  // workspace is an internally-stored double-valued array of length num_vertices+2
  // that is used by some geometry routines
  prsm->workspace.num_items = num_vertices + 2;
  prsm->workspace.items = (double *)malloc((num_vertices + 2) * sizeof(double));
}

/***************************************************************/
/* routines called from C++ or python codes to create prisms   */
/***************************************************************/
// prism with center determined automatically from vertices, height, and axis
geometric_object make_prism(material_type material, const vector3 *vertices, int num_vertices,
                            double height, vector3 axis) {
  return make_prism_with_center(material, auto_center, vertices, num_vertices, height, axis);
}

// prism in which all vertices are translated to ensure that the prism is centered at center.
geometric_object make_prism_with_center(material_type material, vector3 center, const vector3 *vertices,
                                        int num_vertices, double height, vector3 axis) {
  return make_slanted_prism_with_center(material, center, vertices, num_vertices, height, axis, 0);
}

// slanted prism with center determined automatically from vertices, height, axis, and sidewall_angle
geometric_object make_slanted_prism(material_type material, const vector3 *vertices,
                                    int num_vertices, double height, vector3 axis, double sidewall_angle) {
  return make_slanted_prism_with_center(material, auto_center, vertices, num_vertices, height, axis, sidewall_angle);
}

// Have both make_prism_with_center and make_slanted_prism_with_center keep the same parameters to maintain ABI
// compatibility, though make_prism_with_center just calls make_slanted_prism_with_center with the sidewall angle equal
// to zero. To make a slanted prism, the user will have to call make_slanted_prism for now.
geometric_object make_slanted_prism_with_center(material_type material, vector3 center, const vector3 *vertices,
                                                int num_vertices, double height, vector3 axis, double sidewall_angle) {
  geometric_object o = make_geometric_object(material, center);
  o.which_subclass = GEOM PRISM;
  prism *prsm = o.subclass.prism_data = MALLOC1(prism);
  CHECK(prsm, "out of memory");
  prsm->vertices.num_items = num_vertices;
  prsm->vertices.items = (vector3 *)malloc(num_vertices * sizeof(vector3));
  CHECK(prsm->vertices.items, "out of memory");
  memcpy(prsm->vertices.items, vertices, num_vertices * sizeof(vector3));
  prsm->height = height;
  prsm->axis = axis;
  prsm->sidewall_angle = sidewall_angle;
  init_prism(&o);
  return o;
}