Faset_Engine/shaders/temporal.slang

// Temporal scene resolve and full-resolution composite. No material/lighting
// descriptors are consumed here; the scene was shaded before this pass.
// Velocity target: xy = current-minus-prior scene-local UV, z = expected prior
// clip depth, w = opaque motion validity (zero for reactive/invalid pixels).
#if defined(FASET_TEMPORAL_RESOLVE)
struct TemporalResolveParameters {
    uint4 dimensions;         // output width/height, internal width/height
    float4 outputSceneRect;   // output-pixel x/y/width/height
    float4 internalSceneRect; // internal-pixel x/y/width/height
    uint4 flags;              // x = prior history valid
};
[[vk::push_constant]] ConstantBuffer<TemporalResolveParameters> temporalParameters;
[[vk::binding(0,0)]] Texture2D<float4> currentSceneColor;
[[vk::binding(1,0)]] Texture2D<float> currentSceneDepth;
[[vk::binding(2,0)]] Texture2D<float4> currentSceneVelocity;
[[vk::binding(3,0)]] Texture2D<float4> previousHistoryColor;
[[vk::binding(4,0)]] Texture2D<float> previousHistoryDepth;
[[vk::binding(5,0)]] [vk::image_format("rgba16f")]
RWTexture2D<float4> nextHistoryColor;
[[vk::binding(6,0)]] [vk::image_format("r32f")]
RWTexture2D<float> nextHistoryDepth;

int2 clampScenePixel(int2 pixel) {
    return clamp(pixel, int2(0), int2(temporalParameters.dimensions.zw) - 1);
}
float4 sceneColorAt(int2 pixel) {
    return currentSceneColor.Load(int3(clampScenePixel(pixel), 0));
}
float sceneDepthAt(int2 pixel) {
    return currentSceneDepth.Load(int3(clampScenePixel(pixel), 0));
}
float4 sceneVelocityAt(int2 pixel) {
    return currentSceneVelocity.Load(int3(clampScenePixel(pixel), 0));
}
float4 historyBilinear(float2 uv) {
    float2 position = uv * float2(temporalParameters.dimensions.xy) - .5;
    int2 base = int2(floor(position));
    float2 fraction = position - float2(base);
    int2 limit = int2(temporalParameters.dimensions.xy) - 1;
    int2 p00 = clamp(base, int2(0), limit);
    int2 p10 = clamp(base + int2(1, 0), int2(0), limit);
    int2 p01 = clamp(base + int2(0, 1), int2(0), limit);
    int2 p11 = clamp(base + int2(1, 1), int2(0), limit);
    float4 top = lerp(previousHistoryColor.Load(int3(p00, 0)),
                      previousHistoryColor.Load(int3(p10, 0)), fraction.x);
    float4 bottom = lerp(previousHistoryColor.Load(int3(p01, 0)),
                         previousHistoryColor.Load(int3(p11, 0)), fraction.x);
    return lerp(top, bottom, fraction.y);
}

[shader("compute")]
[numthreads(8, 8, 1)]
void temporalResolveMain(uint3 dispatchId : SV_DispatchThreadID) {
    const uint2 outputPixel = dispatchId.xy;
    const uint2 outputExtent = temporalParameters.dimensions.xy;
    const uint2 internalExtent = temporalParameters.dimensions.zw;
    if (outputPixel.x >= outputExtent.x || outputPixel.y >= outputExtent.y) return;

    const float2 center = float2(outputPixel) + .5;
    const float4 outputRect = temporalParameters.outputSceneRect;
    const float4 internalRect = temporalParameters.internalSceneRect;
    const bool insideScene = all(center >= outputRect.xy) &&
                             all(center < outputRect.xy + outputRect.zw) &&
                             all(outputRect.zw > 0);
    const float2 sceneLocalUV = insideScene
        ? (center - outputRect.xy) / outputRect.zw : float2(0);
    const float2 internalPosition = insideScene
        ? internalRect.xy + sceneLocalUV * internalRect.zw
        : center / float2(outputExtent) * float2(internalExtent);
    const int2 currentPixel = clampScenePixel(int2(floor(internalPosition)));
    const float4 currentColor = sceneColorAt(currentPixel);
    const float currentDepth = sceneDepthAt(currentPixel);
    float4 resolved = currentColor;

    if (insideScene && temporalParameters.flags.x != 0) {
        const float4 centerMotion = sceneVelocityAt(currentPixel);
        if (all(isfinite(centerMotion)) && centerMotion.w > 0 &&
            centerMotion.z >= 0 && centerMotion.z <= 1) {
            float4 selectedMotion = centerMotion;
            float selectedDepth = currentDepth;
            const float currentTolerance = .002 + .01 * currentDepth;
            [unroll] for (int dy = -1; dy <= 1; ++dy)
                [unroll] for (int dx = -1; dx <= 1; ++dx) {
                    const int2 neighbor = clampScenePixel(currentPixel + int2(dx, dy));
                    const float depth = sceneDepthAt(neighbor);
                    const float4 motion = sceneVelocityAt(neighbor);
                    if (all(isfinite(motion)) && motion.w > 0 && motion.z >= 0 &&
                        motion.z <= 1 && abs(depth - currentDepth) <= currentTolerance &&
                        depth < selectedDepth) {
                        selectedDepth = depth;
                        selectedMotion = motion;
                    }
                }
            const float2 previousLocalUV = sceneLocalUV - selectedMotion.xy;
            if (all(isfinite(previousLocalUV)) && all(previousLocalUV >= 0) &&
                all(previousLocalUV < 1)) {
                const float2 previousOutputUV =
                    (outputRect.xy + previousLocalUV * outputRect.zw) / float2(outputExtent);
                if (all(previousOutputUV >= 0) && all(previousOutputUV < 1)) {
                    const int2 priorPixel = clamp(
                        int2(floor(previousOutputUV * float2(outputExtent))), int2(0),
                        int2(outputExtent) - 1);
                    const float priorDepth = previousHistoryDepth.Load(int3(priorPixel, 0));
                    const float depthTolerance = .002 + .01 * selectedMotion.z;
                    if (isfinite(priorDepth) &&
                        abs(priorDepth - selectedMotion.z) <= depthTolerance) {
                        float3 low = float3(1e30), high = float3(-1e30);
                        [unroll] for (int dy = -1; dy <= 1; ++dy)
                            [unroll] for (int dx = -1; dx <= 1; ++dx) {
                                const float3 color = sceneColorAt(currentPixel + int2(dx, dy)).rgb;
                                low = min(low, color);
                                high = max(high, color);
                            }
                        const float2 motionPixels = selectedMotion.xy * outputRect.zw;
                        const float weight = .9 * saturate(centerMotion.w) /
                                             (1 + .5 * length(motionPixels));
                        const float3 priorColor = clamp(historyBilinear(previousOutputUV).rgb,
                                                        low, high);
                        resolved.rgb = lerp(currentColor.rgb, priorColor, weight);
                    }
                }
            }
        }
    }
    nextHistoryColor[outputPixel] = resolved;
    nextHistoryDepth[outputPixel] = currentDepth;
}

#elif defined(FASET_TEMPORAL_COMPOSITE)
[[vk::binding(0,0)]] Texture2D<float4> resolvedHistoryColor;

[shader("vertex")]
float4 temporalCompositeVertexMain(uint vertexId : SV_VertexID) : SV_Position {
    const float2 position = vertexId == 0 ? float2(-1, -1)
        : vertexId == 1 ? float2(3, -1) : float2(-1, 3);
    return float4(position, 0, 1);
}

[shader("fragment")]
float4 temporalCompositeFragmentMain(float4 position : SV_Position) : SV_Target {
    // Scene shading is already display-referred. No second tone or gamma pass.
    return resolvedHistoryColor.Load(int3(int2(position.xy), 0));
}
#else
#error Select FASET_TEMPORAL_RESOLVE or FASET_TEMPORAL_COMPOSITE.
#endif