1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
//! This example shows how to manually render 2d items using "mid level render apis" with a custom
//! pipeline for 2d meshes.
//! It doesn't use the [`Material2d`] abstraction, but changes the vertex buffer to include vertex color.
//! Check out the "mesh2d" example for simpler / higher level 2d meshes.
//!
//! [`Material2d`]: bevy::sprite::Material2d

use bevy::{
    color::palettes::basic::YELLOW,
    core_pipeline::core_2d::Transparent2d,
    math::FloatOrd,
    prelude::*,
    render::{
        mesh::{GpuMesh, Indices, MeshVertexAttribute},
        render_asset::{RenderAssetUsages, RenderAssets},
        render_phase::{
            AddRenderCommand, DrawFunctions, PhaseItemExtraIndex, SetItemPipeline,
            ViewSortedRenderPhases,
        },
        render_resource::{
            BlendState, ColorTargetState, ColorWrites, Face, FragmentState, FrontFace,
            MultisampleState, PipelineCache, PolygonMode, PrimitiveState, PrimitiveTopology,
            RenderPipelineDescriptor, SpecializedRenderPipeline, SpecializedRenderPipelines,
            TextureFormat, VertexBufferLayout, VertexFormat, VertexState, VertexStepMode,
        },
        texture::BevyDefault,
        view::{ExtractedView, ViewTarget, VisibleEntities},
        Extract, Render, RenderApp, RenderSet,
    },
    sprite::{
        extract_mesh2d, DrawMesh2d, Material2dBindGroupId, Mesh2dHandle, Mesh2dPipeline,
        Mesh2dPipelineKey, Mesh2dTransforms, MeshFlags, RenderMesh2dInstance, SetMesh2dBindGroup,
        SetMesh2dViewBindGroup, WithMesh2d,
    },
    utils::EntityHashMap,
};
use std::f32::consts::PI;

fn main() {
    App::new()
        .add_plugins((DefaultPlugins, ColoredMesh2dPlugin))
        .add_systems(Startup, star)
        .run();
}

fn star(
    mut commands: Commands,
    // We will add a new Mesh for the star being created
    mut meshes: ResMut<Assets<Mesh>>,
) {
    // Let's define the mesh for the object we want to draw: a nice star.
    // We will specify here what kind of topology is used to define the mesh,
    // that is, how triangles are built from the vertices. We will use a
    // triangle list, meaning that each vertex of the triangle has to be
    // specified. We set `RenderAssetUsages::RENDER_WORLD`, meaning this mesh
    // will not be accessible in future frames from the `meshes` resource, in
    // order to save on memory once it has been uploaded to the GPU.
    let mut star = Mesh::new(
        PrimitiveTopology::TriangleList,
        RenderAssetUsages::RENDER_WORLD,
    );

    // Vertices need to have a position attribute. We will use the following
    // vertices (I hope you can spot the star in the schema).
    //
    //        1
    //
    //     10   2
    // 9      0      3
    //     8     4
    //        6
    //   7        5
    //
    // These vertices are specified in 3D space.
    let mut v_pos = vec![[0.0, 0.0, 0.0]];
    for i in 0..10 {
        // The angle between each vertex is 1/10 of a full rotation.
        let a = i as f32 * PI / 5.0;
        // The radius of inner vertices (even indices) is 100. For outer vertices (odd indices) it's 200.
        let r = (1 - i % 2) as f32 * 100.0 + 100.0;
        // Add the vertex position.
        v_pos.push([r * a.sin(), r * a.cos(), 0.0]);
    }
    // Set the position attribute
    star.insert_attribute(Mesh::ATTRIBUTE_POSITION, v_pos);
    // And a RGB color attribute as well
    let mut v_color: Vec<u32> = vec![LinearRgba::BLACK.as_u32()];
    v_color.extend_from_slice(&[LinearRgba::from(YELLOW).as_u32(); 10]);
    star.insert_attribute(
        MeshVertexAttribute::new("Vertex_Color", 1, VertexFormat::Uint32),
        v_color,
    );

    // Now, we specify the indices of the vertex that are going to compose the
    // triangles in our star. Vertices in triangles have to be specified in CCW
    // winding (that will be the front face, colored). Since we are using
    // triangle list, we will specify each triangle as 3 vertices
    //   First triangle: 0, 2, 1
    //   Second triangle: 0, 3, 2
    //   Third triangle: 0, 4, 3
    //   etc
    //   Last triangle: 0, 1, 10
    let mut indices = vec![0, 1, 10];
    for i in 2..=10 {
        indices.extend_from_slice(&[0, i, i - 1]);
    }
    star.insert_indices(Indices::U32(indices));

    // We can now spawn the entities for the star and the camera
    commands.spawn((
        // We use a marker component to identify the custom colored meshes
        ColoredMesh2d,
        // The `Handle<Mesh>` needs to be wrapped in a `Mesh2dHandle` to use 2d rendering instead of 3d
        Mesh2dHandle(meshes.add(star)),
        // This bundle's components are needed for something to be rendered
        SpatialBundle::INHERITED_IDENTITY,
    ));

    // Spawn the camera
    commands.spawn(Camera2dBundle::default());
}

/// A marker component for colored 2d meshes
#[derive(Component, Default)]
pub struct ColoredMesh2d;

/// Custom pipeline for 2d meshes with vertex colors
#[derive(Resource)]
pub struct ColoredMesh2dPipeline {
    /// this pipeline wraps the standard [`Mesh2dPipeline`]
    mesh2d_pipeline: Mesh2dPipeline,
}

impl FromWorld for ColoredMesh2dPipeline {
    fn from_world(world: &mut World) -> Self {
        Self {
            mesh2d_pipeline: Mesh2dPipeline::from_world(world),
        }
    }
}

// We implement `SpecializedPipeline` to customize the default rendering from `Mesh2dPipeline`
impl SpecializedRenderPipeline for ColoredMesh2dPipeline {
    type Key = Mesh2dPipelineKey;

    fn specialize(&self, key: Self::Key) -> RenderPipelineDescriptor {
        // Customize how to store the meshes' vertex attributes in the vertex buffer
        // Our meshes only have position and color
        let formats = vec![
            // Position
            VertexFormat::Float32x3,
            // Color
            VertexFormat::Uint32,
        ];

        let vertex_layout =
            VertexBufferLayout::from_vertex_formats(VertexStepMode::Vertex, formats);

        let format = match key.contains(Mesh2dPipelineKey::HDR) {
            true => ViewTarget::TEXTURE_FORMAT_HDR,
            false => TextureFormat::bevy_default(),
        };

        RenderPipelineDescriptor {
            vertex: VertexState {
                // Use our custom shader
                shader: COLORED_MESH2D_SHADER_HANDLE,
                entry_point: "vertex".into(),
                shader_defs: vec![],
                // Use our custom vertex buffer
                buffers: vec![vertex_layout],
            },
            fragment: Some(FragmentState {
                // Use our custom shader
                shader: COLORED_MESH2D_SHADER_HANDLE,
                shader_defs: vec![],
                entry_point: "fragment".into(),
                targets: vec![Some(ColorTargetState {
                    format,
                    blend: Some(BlendState::ALPHA_BLENDING),
                    write_mask: ColorWrites::ALL,
                })],
            }),
            // Use the two standard uniforms for 2d meshes
            layout: vec![
                // Bind group 0 is the view uniform
                self.mesh2d_pipeline.view_layout.clone(),
                // Bind group 1 is the mesh uniform
                self.mesh2d_pipeline.mesh_layout.clone(),
            ],
            push_constant_ranges: vec![],
            primitive: PrimitiveState {
                front_face: FrontFace::Ccw,
                cull_mode: Some(Face::Back),
                unclipped_depth: false,
                polygon_mode: PolygonMode::Fill,
                conservative: false,
                topology: key.primitive_topology(),
                strip_index_format: None,
            },
            depth_stencil: None,
            multisample: MultisampleState {
                count: key.msaa_samples(),
                mask: !0,
                alpha_to_coverage_enabled: false,
            },
            label: Some("colored_mesh2d_pipeline".into()),
        }
    }
}

// This specifies how to render a colored 2d mesh
type DrawColoredMesh2d = (
    // Set the pipeline
    SetItemPipeline,
    // Set the view uniform as bind group 0
    SetMesh2dViewBindGroup<0>,
    // Set the mesh uniform as bind group 1
    SetMesh2dBindGroup<1>,
    // Draw the mesh
    DrawMesh2d,
);

// The custom shader can be inline like here, included from another file at build time
// using `include_str!()`, or loaded like any other asset with `asset_server.load()`.
const COLORED_MESH2D_SHADER: &str = r"
// Import the standard 2d mesh uniforms and set their bind groups
#import bevy_sprite::mesh2d_functions

// The structure of the vertex buffer is as specified in `specialize()`
struct Vertex {
    @builtin(instance_index) instance_index: u32,
    @location(0) position: vec3<f32>,
    @location(1) color: u32,
};

struct VertexOutput {
    // The vertex shader must set the on-screen position of the vertex
    @builtin(position) clip_position: vec4<f32>,
    // We pass the vertex color to the fragment shader in location 0
    @location(0) color: vec4<f32>,
};

/// Entry point for the vertex shader
@vertex
fn vertex(vertex: Vertex) -> VertexOutput {
    var out: VertexOutput;
    // Project the world position of the mesh into screen position
    let model = mesh2d_functions::get_world_from_local(vertex.instance_index);
    out.clip_position = mesh2d_functions::mesh2d_position_local_to_clip(model, vec4<f32>(vertex.position, 1.0));
    // Unpack the `u32` from the vertex buffer into the `vec4<f32>` used by the fragment shader
    out.color = vec4<f32>((vec4<u32>(vertex.color) >> vec4<u32>(0u, 8u, 16u, 24u)) & vec4<u32>(255u)) / 255.0;
    return out;
}

// The input of the fragment shader must correspond to the output of the vertex shader for all `location`s
struct FragmentInput {
    // The color is interpolated between vertices by default
    @location(0) color: vec4<f32>,
};

/// Entry point for the fragment shader
@fragment
fn fragment(in: FragmentInput) -> @location(0) vec4<f32> {
    return in.color;
}
";

/// Plugin that renders [`ColoredMesh2d`]s
pub struct ColoredMesh2dPlugin;

/// Handle to the custom shader with a unique random ID
pub const COLORED_MESH2D_SHADER_HANDLE: Handle<Shader> =
    Handle::weak_from_u128(13828845428412094821);

/// Our custom pipeline needs its own instance storage
#[derive(Resource, Deref, DerefMut, Default)]
pub struct RenderColoredMesh2dInstances(EntityHashMap<Entity, RenderMesh2dInstance>);

impl Plugin for ColoredMesh2dPlugin {
    fn build(&self, app: &mut App) {
        // Load our custom shader
        let mut shaders = app.world_mut().resource_mut::<Assets<Shader>>();
        shaders.insert(
            &COLORED_MESH2D_SHADER_HANDLE,
            Shader::from_wgsl(COLORED_MESH2D_SHADER, file!()),
        );

        // Register our custom draw function, and add our render systems
        app.get_sub_app_mut(RenderApp)
            .unwrap()
            .add_render_command::<Transparent2d, DrawColoredMesh2d>()
            .init_resource::<SpecializedRenderPipelines<ColoredMesh2dPipeline>>()
            .init_resource::<RenderColoredMesh2dInstances>()
            .add_systems(
                ExtractSchedule,
                extract_colored_mesh2d.after(extract_mesh2d),
            )
            .add_systems(Render, queue_colored_mesh2d.in_set(RenderSet::QueueMeshes));
    }

    fn finish(&self, app: &mut App) {
        // Register our custom pipeline
        app.get_sub_app_mut(RenderApp)
            .unwrap()
            .init_resource::<ColoredMesh2dPipeline>();
    }
}

/// Extract the [`ColoredMesh2d`] marker component into the render app
pub fn extract_colored_mesh2d(
    mut commands: Commands,
    mut previous_len: Local<usize>,
    // When extracting, you must use `Extract` to mark the `SystemParam`s
    // which should be taken from the main world.
    query: Extract<
        Query<(Entity, &ViewVisibility, &GlobalTransform, &Mesh2dHandle), With<ColoredMesh2d>>,
    >,
    mut render_mesh_instances: ResMut<RenderColoredMesh2dInstances>,
) {
    let mut values = Vec::with_capacity(*previous_len);
    for (entity, view_visibility, transform, handle) in &query {
        if !view_visibility.get() {
            continue;
        }

        let transforms = Mesh2dTransforms {
            world_from_local: (&transform.affine()).into(),
            flags: MeshFlags::empty().bits(),
        };

        values.push((entity, ColoredMesh2d));
        render_mesh_instances.insert(
            entity,
            RenderMesh2dInstance {
                mesh_asset_id: handle.0.id(),
                transforms,
                material_bind_group_id: Material2dBindGroupId::default(),
                automatic_batching: false,
            },
        );
    }
    *previous_len = values.len();
    commands.insert_or_spawn_batch(values);
}

/// Queue the 2d meshes marked with [`ColoredMesh2d`] using our custom pipeline and draw function
#[allow(clippy::too_many_arguments)]
pub fn queue_colored_mesh2d(
    transparent_draw_functions: Res<DrawFunctions<Transparent2d>>,
    colored_mesh2d_pipeline: Res<ColoredMesh2dPipeline>,
    mut pipelines: ResMut<SpecializedRenderPipelines<ColoredMesh2dPipeline>>,
    pipeline_cache: Res<PipelineCache>,
    msaa: Res<Msaa>,
    render_meshes: Res<RenderAssets<GpuMesh>>,
    render_mesh_instances: Res<RenderColoredMesh2dInstances>,
    mut transparent_render_phases: ResMut<ViewSortedRenderPhases<Transparent2d>>,
    mut views: Query<(Entity, &VisibleEntities, &ExtractedView)>,
) {
    if render_mesh_instances.is_empty() {
        return;
    }
    // Iterate each view (a camera is a view)
    for (view_entity, visible_entities, view) in &mut views {
        let Some(transparent_phase) = transparent_render_phases.get_mut(&view_entity) else {
            continue;
        };

        let draw_colored_mesh2d = transparent_draw_functions.read().id::<DrawColoredMesh2d>();

        let mesh_key = Mesh2dPipelineKey::from_msaa_samples(msaa.samples())
            | Mesh2dPipelineKey::from_hdr(view.hdr);

        // Queue all entities visible to that view
        for visible_entity in visible_entities.iter::<WithMesh2d>() {
            if let Some(mesh_instance) = render_mesh_instances.get(visible_entity) {
                let mesh2d_handle = mesh_instance.mesh_asset_id;
                let mesh2d_transforms = &mesh_instance.transforms;
                // Get our specialized pipeline
                let mut mesh2d_key = mesh_key;
                if let Some(mesh) = render_meshes.get(mesh2d_handle) {
                    mesh2d_key |=
                        Mesh2dPipelineKey::from_primitive_topology(mesh.primitive_topology());
                }

                let pipeline_id =
                    pipelines.specialize(&pipeline_cache, &colored_mesh2d_pipeline, mesh2d_key);

                let mesh_z = mesh2d_transforms.world_from_local.translation.z;
                transparent_phase.add(Transparent2d {
                    entity: *visible_entity,
                    draw_function: draw_colored_mesh2d,
                    pipeline: pipeline_id,
                    // The 2d render items are sorted according to their z value before rendering,
                    // in order to get correct transparency
                    sort_key: FloatOrd(mesh_z),
                    // This material is not batched
                    batch_range: 0..1,
                    extra_index: PhaseItemExtraIndex::NONE,
                });
            }
        }
    }
}