UnityCACAO-HDRP17/com.unity.render-pipelines.high-definition/Runtime/Lighting/VolumetricClouds/VolumetricCloudsTraceShadows.compute

#pragma only_renderers d3d11 playstation xboxone xboxseries vulkan metal switch

// Shadows
#pragma kernel TraceVolumetricCloudsShadows

#pragma multi_compile _ CLOUDS_SIMPLE_PRESET

// #pragma enable_d3d11_debug_symbols

#define TRACE_CLOUDS_SHADOWS 1
#include "Packages/com.unity.render-pipelines.core/ShaderLibrary/Common.hlsl"
#include "Packages/com.unity.render-pipelines.high-definition/Runtime/Lighting/VolumetricClouds/VolumetricCloudsUtilities.hlsl"

RW_TEXTURE2D(float4, _VolumetricCloudsShadowRW);

[numthreads(8, 8, 1)]
void TraceVolumetricCloudsShadows(uint3 currentCoords : SV_DispatchThreadID, int groupIndex : SV_GroupIndex)
{
    // If we can, load the cloud lut into the LDS
    #if defined(CLOUDS_SIMPLE_PRESET)
    LoadCloudLutToLDS(groupIndex);
    #endif

    // Compute the normalized coordinate on the shadow plane
    float2 normalizedCoord = currentCoords.xy / (float)(_ShadowCookieResolution - 1);

    // Compute the origin of the ray properties in the planet space
    float3 rayOriginPS = _CloudShadowSunOrigin.xyz + (normalizedCoord.x * _CloudShadowSunRight.xyz + normalizedCoord.y * _CloudShadowSunUp.xyz);
    float3 rayDirection = _CloudShadowSunForward.xyz;

    // Compute the attenuation
    float transmittance = 1.0f;
    float closestDistance = FLT_MAX;
    float farthestDistance = 0.0;
    bool validShadow = false;

    // Intersect the outer sphere
    float radialDistance = length(rayOriginPS);
    float cosChi = dot(rayOriginPS, rayDirection) * rcp(radialDistance);
    float2 tInner = IntersectSphere(_LowestCloudAltitude, cosChi, radialDistance);
    float2 tOuter = IntersectSphere(_HighestCloudAltitude, cosChi, radialDistance);
    if (tInner.y >= 0.0 && tOuter.y >= 0.0)
    {
        // Compute the integration range
        float startDistance = tInner.y;
        float totalDistance = tOuter.y - tInner.y;

        float stepSize = totalDistance / 16;

        for (int i = 1; i < 16; ++i)
        {
            // Compute the sphere intersection position
            float dist = (startDistance + stepSize * i);
            float3 positionPS = rayOriginPS + rayDirection * dist;

            // Get the coverage at intersection point
            CloudCoverageData cloudCoverageData;
            GetCloudCoverageData(positionPS, cloudCoverageData);

            // Compute the cloud density
            CloudProperties cloudProperties;
            EvaluateCloudProperties(positionPS, 0.0, 0.0, true, true, cloudProperties);

            // Apply the camera fade it to match the clouds perceived by the camera
            cloudProperties.density *= DensityFadeValue(length(positionPS - _CameraPositionPS.xyz));

            if (cloudProperties.density > CLOUD_DENSITY_TRESHOLD)
            {
                // Apply the extinction
                closestDistance = min(closestDistance, startDistance + stepSize * (i - 1));
                farthestDistance = max(farthestDistance, startDistance + stepSize * i);
                const float3 currentStepExtinction = exp(-_ScatteringTint.xyz * cloudProperties.density * cloudProperties.sigmaT * stepSize);
                transmittance *= Luminance(currentStepExtinction);
                validShadow = true;
            }
        }
    }
    // If we didn't manage to hit a non null density, we need to fix the distances
    float4 result = validShadow ? float4(1.0 / closestDistance, lerp(1.0 - _ShadowIntensity, 1.0, transmittance), 1.0 / farthestDistance, 1.0) : float4(0.0, 1.0, 0.0, 0.0);

    _VolumetricCloudsShadowRW[currentCoords.xy] = result;
}