Add OMI_physics_body extension validation

lib/src/errors.dart

@@ -554,6 +554,27 @@ class SemanticError extends IssueType {
               'interior volume and the trigger may not work as expected.',
           Severity.Information);
 
+  static final SemanticError omiPhysicsBodyInvalidNode =
+      SemanticError._(
+          'OMI_PHYSICS_BODY_INVALID_NODE',
+          (args) => 'A physics body must be on its own node, it cannot be '
+              'on a node with other components such as a mesh or camera.',
+          Severity.Error);
+
+  static final SemanticError omiPhysicsBodyMissingCollider =
+      SemanticError._(
+          'OMI_PHYSICS_BODY_MISSING_COLLIDER',
+          (args) => 'This physics body does not have any colliders. '
+              'This is valid but body will not collide with anything.',
+          Severity.Information);
+
+  static final SemanticError omiPhysicsBodyInvalidInertiaTensor =
+      SemanticError._(
+          'OMI_PHYSICS_BODY_INVALID_INERTIA_TENSOR',
+          (args) => 'This physics body has an invalid inertia tensor. '
+              'The inertia tensor must be a symmetric 3x3 matrix.',
+          Severity.Error);
+
   SemanticError._(String type, ErrorFunction message,
       [Severity severity = Severity.Error])
       : super(type, message, severity);

lib/src/ext/OMI_physics_body/omi_physics_body.dart

@@ -0,0 +1,132 @@
+// Copyright 2022 The Khronos Group Inc.
+//
+// SPDX-License-Identifier: Apache-2.0
+
+library gltf.extensions.omi_physics_body;
+
+import 'package:gltf/src/base/gltf_property.dart';
+import 'package:gltf/src/ext/extensions.dart';
+
+const String OMI_PHYSICS_BODY = 'OMI_physics_body';
+
+const String MASS = 'mass';
+const String LINEAR_VELOCITY = 'linearVelocity';
+const String ANGULAR_VELOCITY = 'angularVelocity';
+const String INERTIA_TENSOR = 'inertiaTensor';
+
+const String STATIC = 'static';
+const String KINEMATIC = 'kinematic';
+const String CHARACTER = 'character';
+const String RIGID = 'rigid';
+const String VEHICLE = 'vehicle';
+const String TRIGGER = 'trigger';
+
+const List<String> OMI_PHYSICS_BODY_MEMBERS = <String>[
+  TYPE,
+  MASS,
+  LINEAR_VELOCITY,
+  ANGULAR_VELOCITY,
+  INERTIA_TENSOR
+];
+
+const List<String> OMI_PHYSICS_BODY_TYPES = <String>[
+  STATIC,
+  KINEMATIC,
+  CHARACTER,
+  RIGID,
+  VEHICLE,
+  TRIGGER
+];
+
+class OmiPhysicsBody extends GltfProperty {
+  final String type;
+  final double mass;
+  final List<double> linearVelocity;
+  final List<double> angularVelocity;
+  final List<double> inertiaTensor;
+
+  OmiPhysicsBody._(this.type, this.mass, this.linearVelocity,
+      this.angularVelocity, this.inertiaTensor,
+      Map<String, Object> extensions, Object extras)
+      : super(extensions, extras);
+
+  static OmiPhysicsBody fromMap(Map<String, Object> map, Context context) {
+    if (context.validate) {
+      checkMembers(map, OMI_PHYSICS_BODY_MEMBERS, context);
+    }
+
+    final type = getString(map, TYPE, context,
+        list: OMI_PHYSICS_BODY_TYPES, req: true);
+
+    final mass = getFloat(map, MASS, context, def: 1);
+
+    final linearVelocity = getFloatList(map, LINEAR_VELOCITY, context,
+        lengthsList: const [3], def: const [0.0, 0.0, 0.0]);
+
+    final angularVelocity = getFloatList(map, ANGULAR_VELOCITY, context,
+        lengthsList: const [3], def: const [0.0, 0.0, 0.0]);
+
+    final inertiaTensor = getFloatList(map, INERTIA_TENSOR, context,
+        lengthsList: const [9], def: const
+        [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]);
+
+    return OmiPhysicsBody._(
+        type,
+        mass,
+        linearVelocity,
+        angularVelocity,
+        inertiaTensor,
+        getExtensions(map, OmiPhysicsBody, context),
+        getExtras(map, context));
+  }
+
+  @override
+  void link(Gltf gltf, Context context) {
+    if (!context.validate) {
+      return;
+    }
+    // Get the glTF node that this physics body is attached to.
+    final path = context.path;
+    if (path.length < 2 || path[0] != 'nodes') {
+      return;
+    }
+    final nodeIndex = int.tryParse(path[1]);
+    if (nodeIndex == null) {
+      return;
+    }
+    final node = gltf.nodes[nodeIndex];
+    // Ensure that the physics body is not on the same node as a mesh or camera.
+    if (node.mesh != null) {
+      context.addIssue(SemanticError.omiPhysicsBodyInvalidNode);
+    }
+    if (node.camera != null) {
+      context.addIssue(SemanticError.omiPhysicsBodyInvalidNode);
+    }
+    // Check that the physics body has at least one collider.
+    var hasCollider = false;
+    if (node.children != null) {
+      for (final child in node.children) {
+        if (child.extensions != null &&
+            child.extensions.containsKey(OMI_COLLIDER)) {
+          hasCollider = true;
+          break;
+        }
+      }
+    }
+    if (!hasCollider) {
+      context.addIssue(SemanticError.omiPhysicsBodyMissingCollider,
+          name: OMI_PHYSICS_BODY);
+    }
+    // Ensure that the inertia tensor is a symmetric matrix.
+    if (inertiaTensor[1] != inertiaTensor[3] ||
+        inertiaTensor[2] != inertiaTensor[6] ||
+        inertiaTensor[5] != inertiaTensor[7]) {
+      context.addIssue(SemanticError.omiPhysicsBodyInvalidInertiaTensor);
+    }
+  }
+}
+
+const Extension omiPhysicsBodyExtension = Extension(
+    OMI_PHYSICS_BODY, <Type, ExtensionDescriptor>{
+  Node: ExtensionDescriptor(OmiPhysicsBody.fromMap)
+});

lib/src/ext/extensions.dart

@@ -33,6 +33,7 @@ import 'package:gltf/src/ext/KHR_materials_volume/khr_materials_volume.dart';
 import 'package:gltf/src/ext/KHR_mesh_quantization/khr_mesh_quantization.dart';
 import 'package:gltf/src/ext/KHR_texture_transform/khr_texture_transform.dart';
 import 'package:gltf/src/ext/OMI_collider/omi_collider.dart';
+import 'package:gltf/src/ext/OMI_physics_body/omi_physics_body.dart';
 import 'package:gltf/src/hash.dart';
 import 'package:meta/meta.dart';
 
@@ -53,6 +54,7 @@ export 'package:gltf/src/ext/KHR_materials_volume/khr_materials_volume.dart';
 export 'package:gltf/src/ext/KHR_mesh_quantization/khr_mesh_quantization.dart';
 export 'package:gltf/src/ext/KHR_texture_transform/khr_texture_transform.dart';
 export 'package:gltf/src/ext/OMI_collider/omi_collider.dart';
+export 'package:gltf/src/ext/OMI_physics_body/omi_physics_body.dart';
 
 class Extension {
   const Extension(this.name, this.functions,
@@ -114,7 +116,8 @@ const List<Extension> kDefaultExtensions = <Extension>[
   khrMaterialsVolumeExtension,
   khrMeshQuantizationExtension,
   khrTextureTransformExtension,
-  omiColliderExtension
+  omiColliderExtension,
+  omiPhysicsBodyExtension
 ];
 
 // https://github.com/KhronosGroup/glTF/blob/main/extensions/Prefixes.md