// WebGPU wavefront raygen. Runs in GENERATE: compute the pinhole camera
// ray and emit it as the pixel's primary ray. Shading happens later in
// SHADE (closesthit/miss). The Payload type is declared in closesthit.wgsl.

fn raygen_main(gid: vec3<u32>) {
    if (gid.x >= wfParams.surfaceW || gid.y >= wfParams.surfaceH) { return; }

    let pixel = vec2<f32>(f32(gid.x), f32(gid.y));
    let resolution = vec2<f32>(f32(wfParams.surfaceW), f32(wfParams.surfaceH));
    let uv  = (pixel + vec2<f32>(0.5)) / resolution;
    let ndc = uv * 2.0 - vec2<f32>(1.0);

    let origin = vec3<f32>(0.0, 0.0, -300.0);
    let aspect = resolution.x / resolution.y;
    let fov = 60.0 * 3.14159265 / 180.0;
    let tanHalfFov = tan(fov * 0.5);

    let direction = normalize(vec3<f32>(
        ndc.x * aspect * tanHalfFov,
        -ndc.y * tanHalfFov,
        1.0,
    ));

    var payload: Payload;
    payload.color = vec3<f32>(0.0);

    rtEmitPrimaryRay(
        origin, 0.001,
        direction, 10000.0,
        0u,            // ray flags
        0xFFu,         // cull mask
        0u, 0u,        // sbtRecordOffset, missIndex
        payload);
}