[D3D9|Решено] Screen Space Ray Traced Shadows

float3 ViewSpace(float2 uv, in float z)
{
  float2 uvScale = float2(-g_mProjInv[0][0], -g_mProjInv[1][1]);
  float linearZ = g_fCameraNear * g_fCameraFar / (z * (g_fCameraFar - g_fCameraNear) - g_fCameraFar);
  return float3(uv * uvScale, 1.0) * linearZ;
}

float3 ProjectionSpace(float3 coord)
{
  float2 uvScale = float2(-g_mProjInv[0][0], -g_mProjInv[1][1]);
  float encodedZ = (g_fCameraNear * g_fCameraFar / coord.z + g_fCameraFar) / (g_fCameraFar - g_fCameraNear);
  return float3(coord.xy / (coord.z * uvScale), encodedZ);
}

float4 ShadowRayCast(float2 uv)
{
  float3 lightDirWorld = normalize(g_vLightDir);
  float4 lightDirView = mul(float4(lightDirWorld, 0.0f), g_mView);

  float z0 = SampleNonLinearDepth(uv);
  float3 rayOriginView = ViewSpace(uv * 2.0 - 1.0, z0);
  
  float3 rayStartClip = ProjectionSpace(rayOriginView);
  float3 rayEndClip = ProjectionSpace(rayOriginView + lightDirView);
  float3 rayStepClip = rayEndClip - rayStartClip;

  float tolerance = pow(abs(1.0 - z0), 1.5);
  float lightContribution = 1.0;
  const uint maxSamples = 25;

  for (uint i = 0; i < maxSamples; ++i)
  {
    rayStartClip += rayStepClip;
    float sampleDepth = SampleNonLinearDepth(rayStartClip.xy * 0.5 + 0.5);
    float depthDiff = sampleDepth - rayStartClip.z;
    lightContribution *= 1.0 - step(depthDiff, 0.0) * step(abs(depthDiff), tolerance);
  }

  return lightContribution;
}