// Placeholder compute shader — stands in for the develop pipeline.
//
// Its only job is to prove the path: a compute shader writes a storage
// texture, and that texture reaches the screen without a CPU round-trip
// (ARCH §6.1). Replaced by real pipeline stages in v0.2.

struct Params {
    width: u32,
    height: u32,
    // Animates so it is visually obvious the compute pass runs every frame
    // rather than a stale texture being redisplayed.
    phase: f32,
    _pad: f32,
}

@group(0) @binding(0) var output: texture_storage_2d<rgba8unorm, write>;
@group(0) @binding(1) var<uniform> params: Params;

@compute @workgroup_size(8, 8, 1)
fn main(@builtin(global_invocation_id) gid: vec3<u32>) {
    if (gid.x >= params.width || gid.y >= params.height) {
        return;
    }

    let uv = vec2<f32>(
        f32(gid.x) / f32(params.width),
        f32(gid.y) / f32(params.height),
    );

    // Warm dark ground with a moving highlight — deliberately unlike a test
    // pattern, so a stuck frame is obvious at a glance.
    let d = distance(uv, vec2<f32>(0.5 + 0.25 * cos(params.phase), 0.5 + 0.25 * sin(params.phase)));
    let glow = 1.0 - smoothstep(0.0, 0.55, d);

    let base = vec3<f32>(0.08, 0.07, 0.06);
    let accent = vec3<f32>(0.69, 0.23, 0.15);
    let rgb = base + accent * glow * (0.35 + 0.65 * uv.y);

    textureStore(output, vec2<i32>(gid.xy), vec4<f32>(rgb, 1.0));
}