shadows_spatiotemporal_filtering.hlsl

// Temporal filtering via an exponential moving average
float alpha = 0.3f; // Temporal fade, trading temporal stability for lag
// Reproject screenTexCoord to where it was last frame
float2 motionVector = gbuffer_motionVectors.SampleLevel(ss, screenTexCoord, 0);
motionVector.y = 1.f - motionVector.y;
motionVector = motionVector * 2.f - 1.0f;

float2 reprojectedTexCoord = screenTexCoord - motionVector;

// Sample the shadow texture from last frame
// Make sure to use a sampler with border color wrapping to avoid artifacts
// The first channel of the output contains shadows for the first/visibility bounce
// The second channel of the output contains shadows in reflections
float2 cLast = InputShadowsLastFrame.SampleLevel(motionSS, reprojectedTexCoord, 0).rg;

float2 shadow = float2(firstBounceShadowAmount, reflectionShadowAmount);
shadow = alpha * (1.0f - shadow) + (1.0f - alpha) * cLast;
// Write shadow to texture which will be denoised and used in shading the current frame
// as well as used as InputShadowsLastFrame the following frame
lOutputShadows[launchIndex] = shadow;