1import bevy_render::view::View;
2import package::fullscreen_vertex_shader::FullscreenVertexOutput;
3import bevy_pbr::render::view_transformations::uv_to_ndc;
4
5struct PreviousViewUniforms {
6    view_from_world: mat4x4<f32>,
7    clip_from_world: mat4x4<f32>,
8    unjittered_clip_from_world: mat4x4<f32>,
9    clip_from_view: mat4x4<f32>,
10    world_from_clip: mat4x4<f32>,
11    view_from_clip: mat4x4<f32>,
12}
13
14@group(0) @binding(0) var<uniform> view: View;
15@group(0) @binding(1) var<uniform> previous_view: PreviousViewUniforms;
16
17/// Writes motion vectors for sky pixels (depth == 0 in reversed-Z) based on camera rotation.
18///
19/// The fullscreen vertex outputs z=0.0, which equals the cleared depth at sky pixels in
20/// reversed-Z. The GreaterEqual depth test passes only where depth == 0, so this only writes
21/// to pixels untouched by geometry.
22@fragment
23fn fragment(in: FullscreenVertexOutput) -> @location(1) vec4<f32> {
24    let clip_pos = uv_to_ndc(in.uv);
25    let world_pos = view.world_from_clip * vec4(clip_pos, 0.0, 1.0);
26    // Use the unjittered matrices on both sides to strip TAA jitter from the motion
27    // vector.
28    let curr_clip_pos = (view.unjittered_clip_from_world * world_pos).xy;
29    let prev_clip_pos = (previous_view.unjittered_clip_from_world * world_pos).xy;
30    let velocity = (curr_clip_pos - prev_clip_pos) * vec2(0.5, -0.5);
31    return vec4(velocity.x, velocity.y, 0.0, 1.0);
32}