BSDF EvaluateLODLightsSpot(Texture2DArray<float4> gobosTexArr, in SpotLightInstanceData spotInstanceData, float isotropicAttenuation, in ShadingArgs args, in const MaterialClosure c, in const MaterialSurface s, float localLightIntensity)
{
BSDF bsdfAccum = GetDefaultBSDFData();
if(isotropicAttenuation == 0.0)
{
return bsdfAccum;
}

const float3 lightPosition = spotInstanceData.worldPos;
const float3 lightDirection = spotInstanceData.dir;

const float3 LCenterUnorm = lightPosition - s.worldEyePos;
const float sqrDistanceToWindowing = dot(LCenterUnorm, LCenterUnorm);
float3 L = normalize(LCenterUnorm);
float lightIntensity = spotInstanceData.intensity localLightIntensity;
float3 lightColor = UnpackInstanceColor(spotInstanceData.colourRGB_flagsA);

const float spotCosOuterAngle = spotInstanceData.spotCosOuterAngle;
const float spotSinOuterAngle = spotInstanceData.spotSinOuterAngle;

float areaRadius = 0.00001f;
if (args.lighting.isShadingGI)
{

areaRadius = max(min(s.surfaceWidth, 5.0), areaRadius);
}
float sqrLightRadius = areaRadius areaRadius;
float diffuseNormalization = 1.0f / (areaRadius areaRadius);

float diffAttenuation = isotropicAttenuation;
float tranAttenuation = isotropicAttenuation;
float specAttenuation = isotropicAttenuation / sqrDistanceToWindowing;

float sinSigmaSqr = sqrLightRadius / (sqrLightRadius + sqrDistanceToWindowing + s.surfaceWidth);
float cosTheta = dot(s.diffN, L);
AreaLightDiffuseIlluminance illuminance = IlluminanceSphereOrDiskTextured(cosTheta, sinSigmaSqr);
isotropicAttenuation = diffuseNormalization illuminance.isotropic;
diffAttenuation = diffuseNormalization illuminance.front;
tranAttenuation = diffuseNormalization illuminance.back;

uint goboIndex = GetGoboIndex(spotInstanceData);
if (goboIndex != 0xffffffff)
{
const float3 lightTangent = spotInstanceData.tangent;
const float3 lightBitangent = cross(lightDirection, lightTangent);
float3 rotatedDiffL = float3(dot(lightBitangent, L), -dot(lightTangent, L), dot(lightDirection, L));
lightColor = ComputeLODLightSpotGobo(gobosTexArr, goboIndex, float2(spotCosOuterAngle, spotSinOuterAngle), rotatedDiffL);
}

float2 animationUV = spotInstanceData.animationUV;
if (IsNonZero(animationUV.x) || IsNonZero(animationUV.y))
{
lightColor = lightMixColorTexture.Sample(MipLinearWrap, animationUV).rgb lightMixIntensityTexture.Sample(MipLinearWrap, animationUV).r;
}

LightBSDFContextParams_Standard lightParams;
lightParams.lightIntensity = lightIntensity;
lightParams.lightColor = lightColor;
lightParams.isotropicAttenuation = isotropicAttenuation;
lightParams.tranAttenuation = tranAttenuation;
lightParams.diffAttenuation = diffAttenuation;
lightParams.specAttenuation = specAttenuation;
lightParams.diffL = L;
lightParams.specL = L;
lightParams.tranL = L;
lightParams.areaLightSinPhi = 0.0;
LightBSDFContext lightCtx = PopulateLightBSDFContext(args.material, c, s, lightParams);

BSDF bsdf = EvaluateBSDF(args, c, s, lightCtx);
ApplyLightToBSDF(bsdf, lightCtx, bsdfAccum);

return bsdfAccum;
}

struct MeshletHeader
{
uint numMeshlets;
bool isUsing16BitIndices;
bool hasBones;
bool hasSingleBone;
uint singleBone;

uint primitiveCount;
uint vertexCount;
uint primitiveOffset;
uint vertexOffset;
uint boneOffset;

uint sphereRadius;

uint firstPrimitiveID;
};

struct MeshletCullData
{
float4 sphere;
float4 cone;

bool coneValid;
};

static const uint MESHLET_BUFFER_HEADER_MESHLET_COUNT_MASK = (1U << 17) - 1;

static const uint MESHLET_BUFFER_HEADER_IS_USING_16_BIT_INDICES = (1U << 31);
static const uint MESHLET_BUFFER_HEADER_HAS_BONES = (1U << 30);
static const uint MESHLET_BUFFER_HEADER_HAS_SINGLE_BONE = (1U << 29);
static const uint MESHLET_BUFFER_HEADER_SINGLE_BONE_SHIFT = 17;
static const uint MESHLET_BUFFER_HEADER_SINGLE_BONE_MASK = 0xfff;

static const uint MESHLET_HEADER_SIZE = 16;