ScriptableRenderPipeline/com.unity.render-pipelines.high-definition/HDRP/Lighting/LightLoop/LightLoop.hlsl

#include "CoreRP/ShaderLibrary/Macros.hlsl"

//-----------------------------------------------------------------------------
// LightLoop
// ----------------------------------------------------------------------------

void ApplyDebug(LightLoopContext lightLoopContext, float3 positionWS, inout float3 diffuseLighting, inout float3 specularLighting)
{
#ifdef DEBUG_DISPLAY
    if (_DebugLightingMode == DEBUGLIGHTINGMODE_DIFFUSE_LIGHTING)
    {
        specularLighting = float3(0.0, 0.0, 0.0); // Disable specular lighting
    }
    else if (_DebugLightingMode == DEBUGLIGHTINGMODE_SPECULAR_LIGHTING)
    {
        diffuseLighting = float3(0.0, 0.0, 0.0); // Disable diffuse lighting
    }
    else if (_DebugLightingMode == DEBUGLIGHTINGMODE_LUX_METER)
    {
        specularLighting = float3(0.0, 0.0, 0.0); // Disable specular lighting
        // Take the luminance
        diffuseLighting = Luminance(diffuseLighting).xxx;
    }
    else if (_DebugLightingMode == DEBUGLIGHTINGMODE_VISUALIZE_CASCADE)
    {
        specularLighting = float3(0.0, 0.0, 0.0);

        const float3 s_CascadeColors[] = {
            float3(1.0, 0.0, 0.0),
            float3(0.0, 1.0, 0.0),
            float3(0.0, 0.0, 1.0),
            float3(1.0, 1.0, 0.0),
            float3(1.0, 1.0, 1.0)
        };

        diffuseLighting = float3(1.0, 1.0, 1.0);
        if (_DirectionalLightCount > 0)
        {
            int shadowIdx = _DirectionalLightDatas[0].shadowIndex;
            float shadow = GetDirectionalShadowAttenuation(lightLoopContext.shadowContext, positionWS, float3(0.0, 1.0, 0.0 ), shadowIdx, -_DirectionalLightDatas[0].forward, float2(0.0, 0.0));
            uint  payloadOffset;
            real  alpha;
            int cascadeCount;
            int shadowSplitIndex = EvalShadow_GetSplitIndex(lightLoopContext.shadowContext, shadowIdx, positionWS, payloadOffset, alpha, cascadeCount);
            if (shadowSplitIndex >= 0)
            {
                diffuseLighting = lerp(s_CascadeColors[shadowSplitIndex], s_CascadeColors[shadowSplitIndex+1], alpha) * shadow;
            }

        }
    }

    // We always apply exposure when in debug mode. The exposure value will be at a neutral 0.0 when not needed.
    diffuseLighting *= exp2(_DebugExposure);
    specularLighting *= exp2(_DebugExposure);
#endif
}

// Factor all test so we can disable it easily
bool IsMatchingLightLayer(uint lightLayers, uint renderingLayers)
{
    return (lightLayers & renderingLayers) != 0;
}

void LightLoop( float3 V, PositionInputs posInput, PreLightData preLightData, BSDFData bsdfData, BuiltinData builtinData, uint featureFlags,
                out float3 diffuseLighting,
                out float3 specularLighting)
{
    LightLoopContext context;
    context.sampleReflection = 0;
    context.shadowContext = InitShadowContext();
    context.contactShadow = InitContactShadow(posInput);

    // This struct is define in the material. the Lightloop must not access it
    // PostEvaluateBSDF call at the end will convert Lighting to diffuse and specular lighting
    AggregateLighting aggregateLighting;
    ZERO_INITIALIZE(AggregateLighting, aggregateLighting); // LightLoop is in charge of initializing the struct

    uint i = 0; // Declare once to avoid the D3D11 compiler warning.

    if (featureFlags & LIGHTFEATUREFLAGS_DIRECTIONAL)
    {
        for (i = 0; i < _DirectionalLightCount; ++i)
        {
            if (IsMatchingLightLayer(_DirectionalLightDatas[i].lightLayers, builtinData.renderingLayers))
            {
                DirectLighting lighting = EvaluateBSDF_Directional(context, V, posInput, preLightData, _DirectionalLightDatas[i], bsdfData, builtinData);
                AccumulateDirectLighting(lighting, aggregateLighting);
            }
        }
    }

    if (featureFlags & LIGHTFEATUREFLAGS_PUNCTUAL)
    {
        uint lightCount, lightStart;

    #ifdef LIGHTLOOP_TILE_PASS
        GetCountAndStart(posInput, LIGHTCATEGORY_PUNCTUAL, lightStart, lightCount);
    #else
        lightCount = _PunctualLightCount;
        lightStart = 0;
    #endif

        for (i = 0; i < lightCount; i++)
        {
            LightData lightData = FetchLight(lightStart, i);

            if (IsMatchingLightLayer(lightData.lightLayers, builtinData.renderingLayers))
            {
                DirectLighting lighting = EvaluateBSDF_Punctual(context, V, posInput, preLightData, lightData, bsdfData, builtinData);
                AccumulateDirectLighting(lighting, aggregateLighting);
            }
        }
    }

    if (featureFlags & LIGHTFEATUREFLAGS_AREA)
    {
        uint lightCount, lightStart;

    #ifdef LIGHTLOOP_TILE_PASS
        GetCountAndStart(posInput, LIGHTCATEGORY_AREA, lightStart, lightCount);
    #else
        lightCount = _AreaLightCount;
        lightStart = _PunctualLightCount;
    #endif

        // COMPILER BEHAVIOR WARNING!
        // If rectangle lights are before line lights, the compiler will duplicate light matrices in VGPR because they are used differently between the two types of lights.
        // By keeping line lights first we avoid this behavior and save substantial register pressure.
        // TODO: This is based on the current Lit.shader and can be different for any other way of implementing area lights, how to be generic and ensure performance ?

        if (lightCount > 0)
        {
            i = 0;

            uint      last      = lightCount - 1;
            LightData lightData = FetchLight(lightStart, i);

            while (i <= last && lightData.lightType == GPULIGHTTYPE_LINE)
            {
                lightData.lightType = GPULIGHTTYPE_LINE; // Enforce constant propagation

                if (IsMatchingLightLayer(lightData.lightLayers, builtinData.renderingLayers))
                {
                    DirectLighting lighting = EvaluateBSDF_Area(context, V, posInput, preLightData, lightData, bsdfData, builtinData);
                    AccumulateDirectLighting(lighting, aggregateLighting);
                }

                lightData = FetchLight(lightStart, min(++i, last));
            }

            while (i <= last) // GPULIGHTTYPE_RECTANGLE
            {
                lightData.lightType = GPULIGHTTYPE_RECTANGLE; // Enforce constant propagation

                if (IsMatchingLightLayer(lightData.lightLayers, builtinData.renderingLayers))
                {
                    DirectLighting lighting = EvaluateBSDF_Area(context, V, posInput, preLightData, lightData, bsdfData, builtinData);
                    AccumulateDirectLighting(lighting, aggregateLighting);
                }

                lightData = FetchLight(lightStart, min(++i, last));
            }
        }
    }

    // Define macro for a better understanding of the loop
#define EVALUATE_BSDF_ENV_SKY(envLightData, TYPE, type) \
        IndirectLighting lighting = EvaluateBSDF_Env(context, V, posInput, preLightData, envLightData, bsdfData, envLightData.influenceShapeType, MERGE_NAME(GPUIMAGEBASEDLIGHTINGTYPE_, TYPE), MERGE_NAME(type, HierarchyWeight)); \
        AccumulateIndirectLighting(lighting, aggregateLighting);

// Environment cubemap test lightlayers, sky don't test it
#define EVALUATE_BSDF_ENV(envLightData, TYPE, type) if (IsMatchingLightLayer(envLightData.lightLayers, builtinData.renderingLayers)) { EVALUATE_BSDF_ENV_SKY(envLightData, TYPE, type) }

    // First loop iteration
    if (featureFlags & (LIGHTFEATUREFLAGS_ENV | LIGHTFEATUREFLAGS_SKY | LIGHTFEATUREFLAGS_SSREFRACTION | LIGHTFEATUREFLAGS_SSREFLECTION))
    {
        float reflectionHierarchyWeight = 0.0; // Max: 1.0
        float refractionHierarchyWeight = 0.0; // Max: 1.0

        uint envLightStart, envLightCount;

        // Fetch first env light to provide the scene proxy for screen space computation
    #ifdef LIGHTLOOP_TILE_PASS
        GetCountAndStart(posInput, LIGHTCATEGORY_ENV, envLightStart, envLightCount);
    #else
        envLightCount = _EnvLightCount;
        envLightStart = 0;
    #endif

        // Reflection / Refraction hierarchy is
        //  1. Screen Space Refraction / Reflection
        //  2. Environment Reflection / Refraction
        //  3. Sky Reflection / Refraction
        EnvLightData envLightData;
        if (envLightCount > 0)
        {
            envLightData = FetchEnvLight(envLightStart, 0);
        }
        else
        {
            envLightData = InitSkyEnvLightData(0);
        }

        if (featureFlags & LIGHTFEATUREFLAGS_SSREFLECTION)
        {
            IndirectLighting lighting = EvaluateBSDF_SSLighting(    context, V, posInput, preLightData, bsdfData, envLightData,
                                                                    GPUIMAGEBASEDLIGHTINGTYPE_REFLECTION, reflectionHierarchyWeight);
            AccumulateIndirectLighting(lighting, aggregateLighting);
        }

        if (featureFlags & LIGHTFEATUREFLAGS_SSREFRACTION)
        {
            IndirectLighting lighting = EvaluateBSDF_SSLighting(    context, V, posInput, preLightData, bsdfData, envLightData,
                                                                    GPUIMAGEBASEDLIGHTINGTYPE_REFRACTION, refractionHierarchyWeight);
            AccumulateIndirectLighting(lighting, aggregateLighting);
        }

        // Reflection probes are sorted by volume (in the increasing order).
        if (featureFlags & LIGHTFEATUREFLAGS_ENV)
        {
            context.sampleReflection = SINGLE_PASS_CONTEXT_SAMPLE_REFLECTION_PROBES;

            // Note: In case of IBL we are sorted from smaller to bigger projected solid angle bounds. We are not sorted by type so we can't do a 'while' approach like for area light.
            for (i = 0; i < envLightCount && reflectionHierarchyWeight < 1.0; ++i)
            {
                EVALUATE_BSDF_ENV(FetchEnvLight(envLightStart, i), REFLECTION, reflection);
            }

            // Refraction probe and reflection probe will process exactly the same weight. It will be good for performance to be able to share this computation
            // However it is hard to deal with the fact that reflectionHierarchyWeight and refractionHierarchyWeight have not the same values, they are independent
            // The refraction probe is rarely used and happen only with sphere shape and high IOR. So we accept the slow path that use more simple code and
            // doesn't affect the performance of the reflection which is more important.
            // We reuse LIGHTFEATUREFLAGS_SSREFRACTION flag as refraction is mainly base on the screen. Would be a waste to not use screen and only cubemap.
            if (featureFlags & LIGHTFEATUREFLAGS_SSREFRACTION)
            {
                for (i = 0; i < envLightCount && refractionHierarchyWeight < 1.0; ++i)
                {
                    EVALUATE_BSDF_ENV(FetchEnvLight(envLightStart, i), REFRACTION, refraction);
                }
            }
        }

        // Only apply the sky IBL if the sky texture is available
        if ((featureFlags & LIGHTFEATUREFLAGS_SKY) && _EnvLightSkyEnabled)
        {
            // The sky is a single cubemap texture separate from the reflection probe texture array (different resolution and compression)
            context.sampleReflection = SINGLE_PASS_CONTEXT_SAMPLE_SKY;

            // The sky data are generated on the fly so the compiler can optimize the code
            EnvLightData envLightSky = InitSkyEnvLightData(0);

            // Only apply the sky if we haven't yet accumulated enough IBL lighting.
            if (reflectionHierarchyWeight < 1.0)
            {
                EVALUATE_BSDF_ENV_SKY(envLightSky, REFLECTION, reflection);
            }

            if (featureFlags & LIGHTFEATUREFLAGS_SSREFRACTION)
            {
                if (refractionHierarchyWeight < 1.0)
                {
                    EVALUATE_BSDF_ENV_SKY(envLightSky, REFRACTION, refraction);
                }
            }
        }
    }
#undef EVALUATE_BSDF_ENV
#undef EVALUATE_BSDF_ENV_SKY    

    // Also Apply indiret diffuse (GI)
    // PostEvaluateBSDF will perform any operation wanted by the material and sum everything into diffuseLighting and specularLighting
    PostEvaluateBSDF(   context, V, posInput, preLightData, bsdfData, builtinData, aggregateLighting,
                        diffuseLighting, specularLighting);

    ApplyDebug(context, posInput.positionWS, diffuseLighting, specularLighting);
}