UnityCACAO-HDRP17/com.unity.render-pipelines.high-definition/Editor/Lighting/VolumetricClouds/CloudMapGenerator.compute

#pragma kernel EvaluateCloudMap

#include "Packages/com.unity.render-pipelines.core/ShaderLibrary/Common.hlsl"

// #pragma enable_d3d11_debug_symbols

CBUFFER_START(UnityCloudMapGenerator)
    int _CloudMapResolution;
    float _CumulusMapMultiplier;
    float _CumulonimbusMapMultiplier;
    float _AltostratusMapMultiplier;
CBUFFER_END

SamplerState linear_repeat_sampler;
Texture2D<float> _CumulusMap;
Texture2D<float> _CumulonimbusMap;
Texture2D<float> _AltostratusMap;
Texture2D<float> _RainMap;
RWTexture2D<float4> _CloudMapTextureRW;

#define ALTOSTRATUS_ONLY_RANGE_MIN (0.0f/256.0f)
#define ALTOSTRATUS_ONLY_RANGE_MAX (32.0f/256.0f)
#define ALTOSTRATUS_ONLY_MAX_HEIGHT 1.0f

#define CUMULUS_ALTOSTRATUS_RANGE_MIN (32.0f/256.0f)
#define CUMULUS_ALTOSTRATUS_RANGE_MAX (64.0f/256.0f)
#define CUMULUS_ALTOSTRATUS_MAX_HEIGHT 1.0f

#define CUMULUS_ONLY_RANGE_MIN (64.0f/256.0f)
#define CUMULUS_ONLY_RANGE_MAX (128.0f/256.0f)
#define CUMULUS_ONLY_MAX_HEIGHT 0.5f

#define CUMULONIMBUS_RANGE_FIRST_MIN (128.0f/256.0f)
#define CUMULONIMBUS_RANGE_SECOND_MIN (130.0f/256.0f)
#define CUMULONIMBUS_RANGE_THIRD_MIN (136.0f/256.0f)
#define CUMULONIMBUS_RANGE_MAX 1.0f
#define CUMULONIMBUS_MAX_HEIGHT 1.0f

float2 NormalizedCoordinates(uint2 coord)
{
    return (coord + 0.5f) / _CloudMapResolution;
}

[numthreads(8, 8, 1)]
void EvaluateCloudMap(uint2 currentCoord : SV_DispatchThreadID)
{
    // If this pixel is not in the range, we are done
    if (any(currentCoord.xy >= (uint2)  _CloudMapResolution))
        return;

    // Compute the normalized coordinate of the current pixel
    float2 normalizedCoord = NormalizedCoordinates(currentCoord.xy);

    // Read all the cloud data
    float2 tapUV = float2(normalizedCoord.x, 1.0 - normalizedCoord.y);
    float cumulusCoverage = _CumulusMap.SampleLevel(linear_repeat_sampler, tapUV, 0) * _CumulusMapMultiplier;
    cumulusCoverage = cumulusCoverage < 0.01 ? 0.0 : cumulusCoverage;

    float cumulonimbusCoverage = _CumulonimbusMap.SampleLevel(linear_repeat_sampler, tapUV, 0);
    cumulonimbusCoverage = cumulonimbusCoverage < 0.01 ? 0.0 : cumulonimbusCoverage;

    float altoStratusCoverage = _AltostratusMap.SampleLevel(linear_repeat_sampler, tapUV, 0) * _AltostratusMapMultiplier;
    altoStratusCoverage = altoStratusCoverage < 0.01 ? 0.0 : altoStratusCoverage;

    float cloudRain = _RainMap.SampleLevel(linear_repeat_sampler, tapUV, 0);

    float cloudCoverage = 0.0;
    float cloudType = 0.0;
    float cloudMaxHeight = 0.0;

    // Cumulonimbus clouds have precedence over all the other clouds
    if (cumulonimbusCoverage * _CumulonimbusMapMultiplier > 0.0)
    {
        cloudType = cumulonimbusCoverage * (CUMULONIMBUS_RANGE_MAX - CUMULONIMBUS_RANGE_FIRST_MIN) + CUMULONIMBUS_RANGE_FIRST_MIN;
        if (cloudType < CUMULONIMBUS_RANGE_SECOND_MIN)
        {
            cloudCoverage = 0.0f;
            cloudMaxHeight = 0.0;
        }
        else if (cloudType < CUMULONIMBUS_RANGE_THIRD_MIN)
        {
            cloudCoverage = lerp(0.0, _CumulonimbusMapMultiplier, (cloudType - CUMULONIMBUS_RANGE_SECOND_MIN) / (CUMULONIMBUS_RANGE_THIRD_MIN - CUMULONIMBUS_RANGE_SECOND_MIN));
            cloudMaxHeight = lerp(0.0, 1.0, (cloudType - CUMULONIMBUS_RANGE_SECOND_MIN) / (CUMULONIMBUS_RANGE_THIRD_MIN - CUMULONIMBUS_RANGE_SECOND_MIN));
        }
        else
        {
            cloudCoverage = lerp(0.0, 0.75, _CumulonimbusMapMultiplier);
            cloudMaxHeight = 1.0f;
        }
    }
    // Cumulus have precedence over stratus
    else if (cumulusCoverage > 0.0)
    {
        if (altoStratusCoverage > 0.0)
        {
            cloudType = 0.5 * (CUMULUS_ALTOSTRATUS_RANGE_MAX - CUMULUS_ALTOSTRATUS_RANGE_MIN) + CUMULUS_ALTOSTRATUS_RANGE_MIN;
            cloudCoverage = max(cumulusCoverage, altoStratusCoverage);
            cloudMaxHeight = CUMULUS_ALTOSTRATUS_MAX_HEIGHT;
        }
        else
        {
            cloudType = 0.5 * (CUMULUS_ONLY_RANGE_MAX - CUMULUS_ONLY_RANGE_MIN) + CUMULUS_ONLY_RANGE_MIN;
            cloudCoverage = cumulusCoverage;
            cloudMaxHeight = CUMULUS_ONLY_MAX_HEIGHT;
        }
    }
    else
    {
        if (altoStratusCoverage > 0.0)
        {
            cloudType = 0.5 * (ALTOSTRATUS_ONLY_RANGE_MAX - ALTOSTRATUS_ONLY_RANGE_MIN) + ALTOSTRATUS_ONLY_RANGE_MIN;
            cloudCoverage = altoStratusCoverage;
            cloudMaxHeight = ALTOSTRATUS_ONLY_MAX_HEIGHT;
        }
        else
        {
            // No clouds were found
            cloudCoverage = 0.0f;
            cloudType = 0.0f;
            cloudMaxHeight = 0.0f;
        }
    }

    _CloudMapTextureRW[currentCoord] = float4(cloudCoverage, cloudRain, cloudType, cloudMaxHeight);
}