1//! This shader is used for the compute_mesh example
2//! The actual work it does is not important for the example and
3//! has been hardcoded to return a cube mesh
4
5struct DataRanges {
6    /// the starting offset of the mesh data in the *vertex_data* storage buffer
7    vertex_start: u32,
8    vertex_end: u32,
9    /// the starting offset of the index data in the *index_data* storage buffer
10    index_start: u32,
11    index_end: u32,
12}
13
14@group(0) @binding(0) var<uniform> data_range: DataRanges;
15@group(0) @binding(1) var<storage, read_write> vertex_data: array<f32>;
16@group(0) @binding(2) var<storage, read_write> index_data: array<u32>;
17
18@compute @workgroup_size(1)
19fn main(@builtin(global_invocation_id) global_id: vec3<u32>) {
20    // this loop is iterating over the full list of (position, normal, uv)
21    // data what we have in `vertices`.
22    // `192` is used because arrayLength on const arrays doesn't work
23    for (var i = 0u; i < 192; i++) {
24        // The vertex_data buffer is bigger than just the mesh we're
25        // processing because Bevy stores meshes in the mesh_allocator
26        // which allocates slabs that each can contain multiple meshes.
27        // This buffer is one slab, and data_range.vertex_start is the
28        // starting offset for the mesh we care about.
29        // So the 0 starting value in the for loop is added to
30        // data_range.vertex_start which means we start writing at the
31        // correct offset.
32        //
33        // The "end" of the available space to write into is known by us
34        // ahead of time in this example, so we know this has enough space,
35        // but you may wish to also check to make sure you are not writing
36        // past the end of the range *because you should not write past the
37        // end of the range ever*. Doing this can overwrite a different
38        // mesh's data.
39        vertex_data[i + data_range.vertex_start] = vertices[i];
40    }
41    // `36` is the length of the `indices` array
42    for (var i = 0u; i < 36; i++) {
43        // This is doing the same as the vertex_data offset described above
44        index_data[i + data_range.index_start] = u32(indices[i]);
45    }
46}
47
48// hardcoded compute shader data.
49/// half the size of the cube
50const half_size = vec3(1.5);
51const min = -half_size;
52const max = half_size;
53
54// Suppose Y-up right hand, and camera look from +Z to -Z
55const vertices = array(
56    // xyz, normal.xyz, uv.xy
57    // Front
58    min.x, min.y, max.z, 0.0, 0.0, 1.0, 0.0, 0.0,
59    max.x, min.y, max.z, 0.0, 0.0, 1.0, 1.0, 0.0,
60    max.x, max.y, max.z, 0.0, 0.0, 1.0, 1.0, 1.0,
61    min.x, max.y, max.z, 0.0, 0.0, 1.0, 0.0, 1.0,
62    // Back
63    min.x, max.y, min.z, 0.0, 0.0, -1.0, 1.0, 0.0,
64    max.x, max.y, min.z, 0.0, 0.0, -1.0, 0.0, 0.0,
65    max.x, min.y, min.z, 0.0, 0.0, -1.0, 0.0, 1.0,
66    min.x, min.y, min.z, 0.0, 0.0, -1.0, 1.0, 1.0,
67    // Right
68    max.x, min.y, min.z, 1.0, 0.0, 0.0, 0.0, 0.0,
69    max.x, max.y, min.z, 1.0, 0.0, 0.0, 1.0, 0.0,
70    max.x, max.y, max.z, 1.0, 0.0, 0.0, 1.0, 1.0,
71    max.x, min.y, max.z, 1.0, 0.0, 0.0, 0.0, 1.0,
72    // Left
73    min.x, min.y, max.z, -1.0, 0.0, 0.0, 1.0, 0.0,
74    min.x, max.y, max.z, -1.0, 0.0, 0.0, 0.0, 0.0,
75    min.x, max.y, min.z, -1.0, 0.0, 0.0, 0.0, 1.0,
76    min.x, min.y, min.z, -1.0, 0.0, 0.0, 1.0, 1.0,
77    // Top
78    max.x, max.y, min.z, 0.0, 1.0, 0.0, 1.0, 0.0,
79    min.x, max.y, min.z, 0.0, 1.0, 0.0, 0.0, 0.0,
80    min.x, max.y, max.z, 0.0, 1.0, 0.0, 0.0, 1.0,
81    max.x, max.y, max.z, 0.0, 1.0, 0.0, 1.0, 1.0,
82    // Bottom
83    max.x, min.y, max.z, 0.0, -1.0, 0.0, 0.0, 0.0,
84    min.x, min.y, max.z, 0.0, -1.0, 0.0, 1.0, 0.0,
85    min.x, min.y, min.z, 0.0, -1.0, 0.0, 1.0, 1.0,
86    max.x, min.y, min.z, 0.0, -1.0, 0.0, 0.0, 1.0
87);
88
89const indices = array(
90    0, 1, 2, 2, 3, 0, // front
91    4, 5, 6, 6, 7, 4, // back
92    8, 9, 10, 10, 11, 8, // right
93    12, 13, 14, 14, 15, 12, // left
94    16, 17, 18, 18, 19, 16, // top
95    20, 21, 22, 22, 23, 20, // bottom
96);