compute-shader mesh generation example

Cargo.toml

@@ -3020,6 +3020,17 @@ description = "A very simple compute shader that writes to a buffer that is read
 category = "Shaders"
 wasm = false
 
+[[example]]
+name = "compute_mesh"
+path = "examples/shader_advanced/compute_mesh.rs"
+doc-scrape-examples = true
+
+[package.metadata.example.compute_mesh]
+name = "Compute Shader Mesh"
+description = "A compute shader that generates a mesh that is controlled by a Handle"
+category = "Shaders"
+wasm = false
+
 [[example]]
 name = "array_texture"
 path = "examples/shader/array_texture.rs"

assets/shaders/compute_mesh.wgsl

@@ -0,0 +1,96 @@
+// This shader is used for the compute_mesh example
+// The actual work it does is not important for the example and
+// has been hardcoded to return a cube mesh
+
+// `vertex_start` is the starting offset of the mesh data in the *vertex_data* storage buffer
+// `index_start` is the starting offset of the index data in the *index_data* storage buffer
+struct DataRanges {
+    vertex_start: u32,
+    vertex_end: u32,
+    index_start: u32,
+    index_end: u32,
+}
+
+@group(0) @binding(0) var<uniform> data_range: DataRanges;
+@group(0) @binding(1) var<storage, read_write> vertex_data: array<f32>;
+@group(0) @binding(2) var<storage, read_write> index_data: array<u32>;
+
+@compute @workgroup_size(1)
+fn main(@builtin(global_invocation_id) global_id: vec3<u32>) {
+    // this loop is iterating over the full list of (position, normal, uv)
+    // data what we have in `vertices`.
+    // `192` is used because arrayLength on const arrays doesn't work
+    for (var i = 0u; i < 192; i++) {
+        // The vertex_data buffer is bigger than just the mesh we're
+        // processing because Bevy stores meshes in the mesh_allocator
+        // which allocates slabs that each can contain multiple meshes.
+        // This buffer is one slab, and data_range.vertex_start is the
+        // starting offset for the mesh we care about.
+        // So the 0 starting value in the for loop is added to 
+        // data_range.vertex_start which means we start writing at the
+        // correct offset.
+        //
+        // The "end" of the available space to write into is known by us
+        // ahead of time in this example, so we know this has enough space,
+        // but you may wish to also check to make sure you are not writing
+        // past the end of the range *because you should not write past the
+        // end of the range ever*. Doing this can overwrite a different
+        // mesh's data.
+        vertex_data[i + data_range.vertex_start] = vertices[i];
+    }
+    // `36` is the length of the `indices` array
+    for (var i = 0u; i < 36; i++) {
+        // This is doing the same as the vertex_data offset described above
+        index_data[i + data_range.index_start] = u32(indices[i]);
+    }
+}
+
+// hardcoded compute shader data.
+// half_size is half the size of the cube
+const half_size = vec3(1.5);
+const min = -half_size;
+const max = half_size;
+
+// Suppose Y-up right hand, and camera look from +Z to -Z
+const vertices = array(
+    // xyz, normal.xyz, uv.xy
+    // Front
+    min.x, min.y, max.z, 0.0, 0.0, 1.0, 0.0, 0.0,
+    max.x, min.y, max.z, 0.0, 0.0, 1.0, 1.0, 0.0,
+    max.x, max.y, max.z, 0.0, 0.0, 1.0, 1.0, 1.0,
+    min.x, max.y, max.z, 0.0, 0.0, 1.0, 0.0, 1.0,
+    // Back
+    min.x, max.y, min.z, 0.0, 0.0, -1.0, 1.0, 0.0,
+    max.x, max.y, min.z, 0.0, 0.0, -1.0, 0.0, 0.0,
+    max.x, min.y, min.z, 0.0, 0.0, -1.0, 0.0, 1.0,
+    min.x, min.y, min.z, 0.0, 0.0, -1.0, 1.0, 1.0,
+    // Right
+    max.x, min.y, min.z, 1.0, 0.0, 0.0, 0.0, 0.0,
+    max.x, max.y, min.z, 1.0, 0.0, 0.0, 1.0, 0.0,
+    max.x, max.y, max.z, 1.0, 0.0, 0.0, 1.0, 1.0,
+    max.x, min.y, max.z, 1.0, 0.0, 0.0, 0.0, 1.0,
+    // Left
+    min.x, min.y, max.z, -1.0, 0.0, 0.0, 1.0, 0.0,
+    min.x, max.y, max.z, -1.0, 0.0, 0.0, 0.0, 0.0,
+    min.x, max.y, min.z, -1.0, 0.0, 0.0, 0.0, 1.0,
+    min.x, min.y, min.z, -1.0, 0.0, 0.0, 1.0, 1.0,
+    // Top
+    max.x, max.y, min.z, 0.0, 1.0, 0.0, 1.0, 0.0,
+    min.x, max.y, min.z, 0.0, 1.0, 0.0, 0.0, 0.0,
+    min.x, max.y, max.z, 0.0, 1.0, 0.0, 0.0, 1.0,
+    max.x, max.y, max.z, 0.0, 1.0, 0.0, 1.0, 1.0,
+    // Bottom
+    max.x, min.y, max.z, 0.0, -1.0, 0.0, 0.0, 0.0,
+    min.x, min.y, max.z, 0.0, -1.0, 0.0, 1.0, 0.0,
+    min.x, min.y, min.z, 0.0, -1.0, 0.0, 1.0, 1.0,
+    max.x, min.y, min.z, 0.0, -1.0, 0.0, 0.0, 1.0
+);
+
+const indices = array(
+    0, 1, 2, 2, 3, 0, // front
+    4, 5, 6, 6, 7, 4, // back
+    8, 9, 10, 10, 11, 8, // right
+    12, 13, 14, 14, 15, 12, // left
+    16, 17, 18, 18, 19, 16, // top
+    20, 21, 22, 22, 23, 20, // bottom
+);

examples/README.md

@@ -467,6 +467,7 @@ Example | Description
 [Animated](../examples/shader/animate_shader.rs) | A shader that uses dynamic data like the time since startup
 [Array Texture](../examples/shader/array_texture.rs) | A shader that shows how to reuse the core bevy PBR shading functionality in a custom material that obtains the base color from an array texture.
 [Compute - Game of Life](../examples/shader/compute_shader_game_of_life.rs) | A compute shader that simulates Conway's Game of Life
+[Compute Shader Mesh](../examples/shader_advanced/compute_mesh.rs) | A compute shader that generates a mesh that is controlled by a Handle
 [Custom Render Phase](../examples/shader_advanced/custom_render_phase.rs) | Shows how to make a complete render phase
 [Custom Vertex Attribute](../examples/shader_advanced/custom_vertex_attribute.rs) | A shader that reads a mesh's custom vertex attribute
 [Custom phase item](../examples/shader_advanced/custom_phase_item.rs) | Demonstrates how to enqueue custom draw commands in a render phase