Boids?

src/main.rs

@@ -1,6 +1,13 @@
-#![allow(unused)]
-
-use bevy::{prelude::*, sprite::MaterialMesh2dBundle};
+use bevy::{
+    color::palettes::tailwind,
+    prelude::*,
+    render::{
+        mesh::{Indices, PrimitiveTopology},
+        render_asset::RenderAssetUsages,
+    },
+    sprite::{MaterialMesh2dBundle, Mesh2dHandle},
+};
+use std::f32::consts::FRAC_PI_2;
 
 fn main() {
     App::new()
@@ -13,8 +20,7 @@ fn main() {
 struct Boid;
 
 struct BoidBundle {
-    outer_mesh: MaterialMesh2dBundle<ColorMaterial>,
-    inner_mesh: MaterialMesh2dBundle<ColorMaterial>,
+    mesh: MaterialMesh2dBundle<ColorMaterial>,
     position: TransformBundle,
     velocity: Vec2,
 }
@@ -25,4 +31,68 @@ fn setup(
     mut materials: ResMut<Assets<ColorMaterial>>,
 ) {
     commands.spawn(Camera2dBundle::default());
+
+    let boid_mesh = make_boid_mesh();
+
+    let boid_color = Color::from(tailwind::NEUTRAL_50);
+    commands.spawn(MaterialMesh2dBundle {
+        mesh: Mesh2dHandle(meshes.add(boid_mesh)),
+        material: materials.add(boid_color),
+        transform: Transform::from_scale(Vec3::splat(2.5)),
+        ..default()
+    });
+}
+
+fn make_boid_mesh() -> Mesh {
+    const TRIANGLE_HEIGHT: f32 = 10.;
+    const TRIANGLE_WIDTH: f32 = 5.;
+    const STROKE_WIDTH: f32 = 0.25;
+
+    const HALF_HEIGHT: f32 = TRIANGLE_HEIGHT / 2.0;
+    const HALF_WIDTH: f32 = TRIANGLE_WIDTH / 2.0;
+
+    let w2 = (HALF_WIDTH * HALF_WIDTH + TRIANGLE_HEIGHT * TRIANGLE_HEIGHT).sqrt();
+    let c = STROKE_WIDTH / (HALF_WIDTH / w2);
+
+    let alpha: f32 = (TRIANGLE_HEIGHT / HALF_WIDTH).atan();
+    let b: f32 = STROKE_WIDTH * (FRAC_PI_2 - (alpha / 2.)).tan();
+
+    let mut boid_mesh = Mesh::new(
+        PrimitiveTopology::TriangleList,
+        RenderAssetUsages::RENDER_WORLD,
+    );
+
+    #[rustfmt::skip]
+    let verts = vec![
+        [0.0, HALF_HEIGHT - c, 0.0],
+        [0.0, HALF_HEIGHT, 0.0],
+        [
+            HALF_WIDTH - b,
+            -HALF_HEIGHT + STROKE_WIDTH,
+            0.0,
+        ],
+        [HALF_WIDTH, -HALF_HEIGHT, 0.0],
+        [
+            -HALF_WIDTH + b,
+            -HALF_HEIGHT + STROKE_WIDTH,
+            0.0,
+        ],
+        [-HALF_WIDTH, -HALF_HEIGHT, 0.0],
+    ];
+
+    boid_mesh.insert_attribute(Mesh::ATTRIBUTE_POSITION, verts);
+
+    #[rustfmt::skip]
+    let indices = vec![
+        0, 1, 5,
+        0, 2, 1,
+        1, 2, 3,
+        0, 5, 4,
+        3, 4, 5,
+        2, 4, 3
+    ];
+
+    boid_mesh.insert_indices(Indices::U32(indices));
+
+    boid_mesh
 }