From f98e5d0318084d502b29c022119a7a8ba8b58ddf Mon Sep 17 00:00:00 2001
From: Martin Indra <martin.indra@mgn.cz>
Date: Mon, 4 Jul 2022 18:51:13 +0200
Subject: [PATCH] Implement laser beam

Relates to #24.
---
 crates/attacking/src/beam.rs  | 186 ++++++++++++++++++++++++++++++++++
 crates/attacking/src/laser.rs |  10 +-
 crates/attacking/src/lib.rs   |   5 +-
 3 files changed, 198 insertions(+), 3 deletions(-)
 create mode 100644 crates/attacking/src/beam.rs

diff --git a/crates/attacking/src/beam.rs b/crates/attacking/src/beam.rs
new file mode 100644
index 00000000..ea176e51
--- /dev/null
+++ b/crates/attacking/src/beam.rs
@@ -0,0 +1,186 @@
+use std::time::Duration;
+
+use bevy::{
+    prelude::*,
+    render::mesh::{Indices, PrimitiveTopology},
+};
+use de_core::state::GameState;
+use iyes_loopless::prelude::*;
+use parry3d::query::Ray;
+
+use crate::AttackingLabels;
+
+/// All but bottom vertex of a hexagon. The hexagon lies on plane perpendicular
+/// to X axis. The vertices start with the bottom-right point.
+///
+/// It  looks like this:
+///
+///   /\
+///  /  \
+/// |    |
+/// |    |
+const HEXAGON_VERTICES: [[f32; 3]; 5] = [
+    [0., -0.25, 0.433],
+    [0., 0.25, 0.433],
+    [0., 0.5, 0.],
+    [0., 0.25, -0.433],
+    [0., -0.25, -0.433],
+];
+
+/// Outwards normals of a hexagon whose base is given by [`HEXAGON_VERTICES`].
+/// The bottom two edges are / surfaces are not included. It starts with normal
+/// of the right (largest Z coordinate) surface.
+const HEXAGON_NORMALS: [[f32; 3]; 4] = [
+    [0., 0., 1.],
+    [0., 0.866_025_4, 0.5],
+    [0., 0.866_025_4, -0.5],
+    [0., 0., -1.],
+];
+
+const BEAM_COLOR: Color = Color::rgba(0.2, 0., 1., 0.4);
+const BEAM_DURATION: Duration = Duration::from_millis(500);
+
+pub(crate) struct BeamPlugin;
+
+impl Plugin for BeamPlugin {
+    fn build(&self, app: &mut App) {
+        app.add_event::<SpawnBeamEvent>()
+            .add_enter_system(GameState::Playing, setup)
+            .add_system_set_to_stage(
+                CoreStage::Update,
+                SystemSet::new()
+                    .with_system(
+                        spawn
+                            .run_in_state(GameState::Playing)
+                            .label(AttackingLabels::Beam),
+                    )
+                    .with_system(despawn.run_in_state(GameState::Playing)),
+            );
+    }
+}
+
+pub(crate) struct SpawnBeamEvent(Ray);
+
+impl SpawnBeamEvent {
+    /// Send this event to spawn a new beam. The beam will automatically
+    /// disappear after a moment.
+    ///
+    /// # Arguments
+    ///
+    /// * `ray` - the beam originates at the ray origin. The beam ends at the
+    ///   `ray.origin + ray.dir`.
+    pub(crate) fn new(ray: Ray) -> Self {
+        Self(ray)
+    }
+
+    fn ray(&self) -> &Ray {
+        &self.0
+    }
+}
+
+struct BeamHandles {
+    material: Handle<StandardMaterial>,
+    mesh: Handle<Mesh>,
+}
+
+#[derive(Component)]
+struct Beam {
+    timer: Timer,
+}
+
+impl Beam {
+    fn new() -> Self {
+        Self {
+            timer: Timer::new(BEAM_DURATION, false),
+        }
+    }
+
+    fn tick(&mut self, duration: Duration) -> bool {
+        self.timer.tick(duration);
+        self.timer.finished()
+    }
+}
+
+fn spawn(
+    mut commands: Commands,
+    handles: Res<BeamHandles>,
+    mut events: EventReader<SpawnBeamEvent>,
+) {
+    for event in events.iter() {
+        commands
+            .spawn_bundle(PbrBundle {
+                mesh: handles.mesh.clone(),
+                material: handles.material.clone(),
+                transform: Transform {
+                    translation: event.ray().origin.into(),
+                    rotation: Quat::from_rotation_arc(Vec3::X, event.ray().dir.normalize().into()),
+                    scale: Vec3::new(event.ray().dir.norm(), 0.1, 0.1),
+                },
+                ..Default::default()
+            })
+            .insert(Beam::new());
+    }
+}
+
+fn despawn(mut commands: Commands, time: Res<Time>, mut query: Query<(Entity, &mut Beam)>) {
+    for (entity, mut beam) in query.iter_mut() {
+        if beam.tick(time.delta()) {
+            commands.entity(entity).despawn_recursive();
+        }
+    }
+}
+
+fn setup(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+) {
+    let material = materials.add(StandardMaterial {
+        base_color: BEAM_COLOR,
+        alpha_mode: AlphaMode::Blend,
+        unlit: true,
+        ..Default::default()
+    });
+    let mesh = meshes.add(generate_beam_mesh());
+    commands.insert_resource(BeamHandles { material, mesh });
+}
+
+/// This generates a beam mesh, consisting of a hexagonal prism without the
+/// bottom two faces.
+///
+/// Width (along Z axis) of the hexagon is 1. Length (along X axis) of the beam
+/// is 1.
+fn generate_beam_mesh() -> Mesh {
+    let mut positions = Vec::with_capacity(16);
+    let mut normals = Vec::with_capacity(positions.len());
+    let mut uvs = Vec::with_capacity(positions.len());
+
+    // First, add base of the beam (a hexagon).
+    for i in 0..4 {
+        positions.push(HEXAGON_VERTICES[i]);
+        positions.push(HEXAGON_VERTICES[i + 1]);
+        normals.push(HEXAGON_NORMALS[i]);
+        normals.push(HEXAGON_NORMALS[i]);
+        uvs.push([0., i as f32 / 4.]);
+        uvs.push([0., (i + 1) as f32 / 4.]);
+    }
+    // Second, add the other end of the beam.
+    for i in 0..positions.len() {
+        positions.push([1., positions[i][1], positions[i][2]]);
+        normals.push(normals[i]);
+        uvs.push([1., uvs[i][1]]);
+    }
+    let indices = Indices::U16(
+        (0..8)
+            .step_by(2)
+            .flat_map(|i| [i, i + 1, i + 8, i + 1, i + 9, i + 8])
+            .collect(),
+    );
+
+    let mut mesh = Mesh::new(PrimitiveTopology::TriangleList);
+    mesh.insert_attribute(Mesh::ATTRIBUTE_POSITION, positions);
+    mesh.insert_attribute(Mesh::ATTRIBUTE_NORMAL, normals);
+    mesh.insert_attribute(Mesh::ATTRIBUTE_UV_0, uvs);
+    mesh.set_indices(Some(indices));
+    mesh
+}
diff --git a/crates/attacking/src/laser.rs b/crates/attacking/src/laser.rs
index 4229d630..727f705a 100644
--- a/crates/attacking/src/laser.rs
+++ b/crates/attacking/src/laser.rs
@@ -5,7 +5,7 @@ use de_spawner::SpawnerLabels;
 use iyes_loopless::prelude::*;
 use parry3d::query::Ray;
 
-use crate::{sightline::LineOfSight, AttackingLabels};
+use crate::{beam::SpawnBeamEvent, sightline::LineOfSight, AttackingLabels};
 
 pub(crate) struct LaserPlugin;
 
@@ -15,7 +15,8 @@ impl Plugin for LaserPlugin {
             CoreStage::Update,
             fire.run_in_state(GameState::Playing)
                 .label(AttackingLabels::Fire)
-                .before(SpawnerLabels::Destroyer),
+                .before(SpawnerLabels::Destroyer)
+                .before(AttackingLabels::Beam),
         );
     }
 }
@@ -74,6 +75,7 @@ impl LaserFireEvent {
 
 fn fire(
     mut fires: EventReader<LaserFireEvent>,
+    mut beams: EventWriter<SpawnBeamEvent>,
     sightline: LineOfSight,
     mut susceptible: Query<&mut Health>,
 ) {
@@ -86,6 +88,10 @@ fn fire(
         }
 
         let observation = sightline.sight(fire.ray(), fire.max_toi(), fire.attacker());
+        beams.send(SpawnBeamEvent::new(Ray::new(
+            fire.ray().origin,
+            observation.toi() * fire.ray().dir,
+        )));
         if let Some(entity) = observation.entity() {
             susceptible.get_mut(entity).unwrap().hit(fire.damage());
         }
diff --git a/crates/attacking/src/lib.rs b/crates/attacking/src/lib.rs
index 981e990f..f52320a7 100644
--- a/crates/attacking/src/lib.rs
+++ b/crates/attacking/src/lib.rs
@@ -1,5 +1,6 @@
 pub use attack::AttackEvent;
 use attack::AttackPlugin;
+use beam::BeamPlugin;
 use bevy::{
     app::PluginGroupBuilder,
     prelude::{PluginGroup, SystemLabel},
@@ -7,6 +8,7 @@ use bevy::{
 use laser::LaserPlugin;
 
 mod attack;
+mod beam;
 mod laser;
 mod sightline;
 
@@ -14,7 +16,7 @@ pub struct AttackingPluginGroup;
 
 impl PluginGroup for AttackingPluginGroup {
     fn build(&mut self, group: &mut PluginGroupBuilder) {
-        group.add(LaserPlugin).add(AttackPlugin);
+        group.add(LaserPlugin).add(AttackPlugin).add(BeamPlugin);
     }
 }
 
@@ -24,4 +26,5 @@ pub enum AttackingLabels {
     Update,
     Aim,
     Fire,
+    Beam,
 }