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// [新增] 运行时 IBL 烘焙 Shader。
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// 使用全屏三角形逐面写入 Cube RTV，不需要额外顶点缓冲。
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#pragma pack_matrix(row_major)
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static const float IBL_PI = 3.14159265359f;
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static const float IBL_EPSILON = 1.0e-5f;
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cbuffer CBBake : register(b0) {
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// x=roughness, y=源 Cube 尺寸, z=源 Cube 最大 mip, w=保留
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float4 gBakeFloatParams;
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// x=目标 face, y=采样数, z/w=保留
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uint4 gBakeUIntParams;
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};
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TextureCube<float4> gSourceEnvironment : register(t0);
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SamplerState gSourceSampler : register(s0);
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struct VSOutput {
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float4 positionCS : SV_POSITION;
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float2 uv : TEXCOORD0;
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};
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VSOutput VSFullscreen(uint vertexId : SV_VertexID) {
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VSOutput output;
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// 一个三角形覆盖整个目标视口。
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const float2 positions[3] = {
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float2(-1.0f, -1.0f),
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float2(-1.0f, 3.0f),
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float2( 3.0f, -1.0f)
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};
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const float2 position = positions[vertexId];
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output.positionCS = float4(position, 0.0f, 1.0f);
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output.uv = float2(position.x * 0.5f + 0.5f,
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0.5f - position.y * 0.5f);
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return output;
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}
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// [新增] 把目标 Cube 某个面的 UV 映射为世界方向。
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// face 顺序必须与 D3D11：+X、-X、+Y、-Y、+Z、-Z 完全一致。
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float3 CubeDirection(uint faceIndex, float2 uv) {
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const float2 ndc = float2(uv.x * 2.0f - 1.0f,
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1.0f - uv.y * 2.0f);
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float3 direction = float3(ndc.x, ndc.y, 1.0f);
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switch (faceIndex) {
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case 0u: direction = float3( 1.0f, ndc.y, -ndc.x); break; // +X
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case 1u: direction = float3(-1.0f, ndc.y, ndc.x); break; // -X
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case 2u: direction = float3( ndc.x, 1.0f, -ndc.y); break; // +Y
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case 3u: direction = float3( ndc.x,-1.0f, ndc.y); break; // -Y
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case 4u: direction = float3( ndc.x, ndc.y, 1.0f); break; // +Z
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case 5u: direction = float3(-ndc.x, ndc.y, -1.0f); break; // -Z
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default: break;
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}
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return normalize(direction);
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}
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float RadicalInverseVdC(uint bits) {
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bits = (bits << 16u) | (bits >> 16u);
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bits = ((bits & 0x55555555u) << 1u) | ((bits & 0xAAAAAAAAu) >> 1u);
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bits = ((bits & 0x33333333u) << 2u) | ((bits & 0xCCCCCCCCu) >> 2u);
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bits = ((bits & 0x0F0F0F0Fu) << 4u) | ((bits & 0xF0F0F0F0u) >> 4u);
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bits = ((bits & 0x00FF00FFu) << 8u) | ((bits & 0xFF00FF00u) >> 8u);
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return float(bits) * 2.3283064365386963e-10f;
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}
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float2 Hammersley(uint index, uint sampleCount) {
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return float2(float(index) / float(sampleCount), RadicalInverseVdC(index));
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}
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void BuildBasis(float3 normal, out float3 tangent, out float3 bitangent) {
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const float3 up = abs(normal.z) < 0.999f
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? float3(0.0f, 0.0f, 1.0f)
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: float3(1.0f, 0.0f, 0.0f);
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tangent = normalize(cross(up, normal));
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bitangent = cross(normal, tangent);
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}
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float3 CosineSampleHemisphere(float2 xi, float3 normal) {
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const float radius = sqrt(xi.y);
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const float phi = 2.0f * IBL_PI * xi.x;
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float sinePhi;
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float cosinePhi;
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sincos(phi, sinePhi, cosinePhi);
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const float3 localDirection = float3(
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radius * cosinePhi,
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radius * sinePhi,
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sqrt(saturate(1.0f - xi.y)));
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float3 tangent;
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float3 bitangent;
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BuildBasis(normal, tangent, bitangent);
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return normalize(
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tangent * localDirection.x +
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bitangent * localDirection.y +
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normal * localDirection.z);
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}
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float3 ImportanceSampleGGX(float2 xi, float3 normal, float roughness) {
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const float alpha = max(roughness * roughness, 0.001f);
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const float alpha2 = alpha * alpha;
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const float phi = 2.0f * IBL_PI * xi.x;
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const float cosTheta = sqrt(
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saturate((1.0f - xi.y) /
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max(1.0f + (alpha2 - 1.0f) * xi.y, IBL_EPSILON)));
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const float sinTheta = sqrt(saturate(1.0f - cosTheta * cosTheta));
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float sinePhi;
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float cosinePhi;
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sincos(phi, sinePhi, cosinePhi);
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const float3 halfVectorTangent = float3(
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cosinePhi * sinTheta,
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sinePhi * sinTheta,
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cosTheta);
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float3 tangent;
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float3 bitangent;
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BuildBasis(normal, tangent, bitangent);
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return normalize(
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tangent * halfVectorTangent.x +
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bitangent * halfVectorTangent.y +
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normal * halfVectorTangent.z);
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}
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float DistributionGGXForPdf(float nDotH, float roughness) {
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const float alpha = max(roughness * roughness, 0.001f);
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const float alpha2 = alpha * alpha;
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const float denominator = nDotH * nDotH * (alpha2 - 1.0f) + 1.0f;
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return alpha2 / max(IBL_PI * denominator * denominator, IBL_EPSILON);
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}
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float4 PSIrradiance(VSOutput input) : SV_TARGET {
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const float3 normal = CubeDirection(gBakeUIntParams.x, input.uv);
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const uint sampleCount = max(gBakeUIntParams.y, 1u);
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float3 irradiance = float3(0.0f, 0.0f, 0.0f);
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[loop]
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for (uint sampleIndex = 0u; sampleIndex < sampleCount; ++sampleIndex) {
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const float2 xi = Hammersley(sampleIndex, sampleCount);
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const float3 lightDirection = CosineSampleHemisphere(xi, normal);
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irradiance += gSourceEnvironment.SampleLevel(
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gSourceSampler, lightDirection, 0.0f).rgb;
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}
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// 这里直接保存 Lambert 卷积后的漫反射环境项 E/PI。
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// 因此运行时只需乘 baseColor，不再额外除以 PI。
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irradiance /= float(sampleCount);
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return float4(irradiance, 1.0f);
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}
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float4 PSPrefilter(VSOutput input) : SV_TARGET {
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const float3 normal = CubeDirection(gBakeUIntParams.x, input.uv);
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const float roughness = saturate(gBakeFloatParams.x);
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// roughness=0 的 mip0 直接保留原环境，避免 GGX 极窄分布的数值误差。
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if (roughness <= 0.001f) {
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return float4(gSourceEnvironment.SampleLevel(
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gSourceSampler, normal, 0.0f).rgb, 1.0f);
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}
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const uint sampleCount = max(gBakeUIntParams.y, 1u);
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const float sourceSize = max(gBakeFloatParams.y, 1.0f);
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const float sourceMaxMip = max(gBakeFloatParams.z, 0.0f);
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const float3 viewDirection = normal;
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float3 prefilteredColor = float3(0.0f, 0.0f, 0.0f);
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float totalWeight = 0.0f;
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const float texelSolidAngle =
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4.0f * IBL_PI / (6.0f * sourceSize * sourceSize);
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[loop]
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for (uint sampleIndex = 0u; sampleIndex < sampleCount; ++sampleIndex) {
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const float2 xi = Hammersley(sampleIndex, sampleCount);
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const float3 halfVector = ImportanceSampleGGX(xi, normal, roughness);
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const float3 lightDirection = normalize(
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2.0f * dot(viewDirection, halfVector) * halfVector - viewDirection);
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const float nDotL = saturate(dot(normal, lightDirection));
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if (nDotL > 0.0f) {
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const float nDotH = saturate(dot(normal, halfVector));
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const float hDotV = saturate(dot(halfVector, viewDirection));
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const float distribution = DistributionGGXForPdf(nDotH, roughness);
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const float pdf = max(
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distribution * nDotH / max(4.0f * hDotV, IBL_EPSILON),
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IBL_EPSILON);
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const float sampleSolidAngle =
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1.0f / (float(sampleCount) * pdf + IBL_EPSILON);
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const float mipLevel = clamp(
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0.5f * log2(max(sampleSolidAngle / texelSolidAngle, IBL_EPSILON)),
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0.0f, sourceMaxMip);
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prefilteredColor += gSourceEnvironment.SampleLevel(
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gSourceSampler, lightDirection, mipLevel).rgb * nDotL;
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totalWeight += nDotL;
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}
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}
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prefilteredColor /= max(totalWeight, IBL_EPSILON);
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return float4(prefilteredColor, 1.0f);
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}
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float GeometrySchlickGGXIBL(float nDotX, float roughness) {
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const float k = (roughness * roughness) * 0.5f;
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return nDotX / max(nDotX * (1.0f - k) + k, IBL_EPSILON);
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}
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float GeometrySmithIBL(float nDotV, float nDotL, float roughness) {
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return GeometrySchlickGGXIBL(nDotV, roughness) *
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GeometrySchlickGGXIBL(nDotL, roughness);
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}
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float2 IntegrateBrdf(float nDotV, float roughness, uint sampleCount) {
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const float3 normal = float3(0.0f, 0.0f, 1.0f);
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const float3 viewDirection = float3(
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sqrt(saturate(1.0f - nDotV * nDotV)), 0.0f, nDotV);
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float scale = 0.0f;
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float bias = 0.0f;
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[loop]
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for (uint sampleIndex = 0u; sampleIndex < sampleCount; ++sampleIndex) {
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const float2 xi = Hammersley(sampleIndex, sampleCount);
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const float3 halfVector = ImportanceSampleGGX(xi, normal, roughness);
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const float3 lightDirection = normalize(
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2.0f * dot(viewDirection, halfVector) * halfVector - viewDirection);
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const float nDotL = saturate(lightDirection.z);
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const float nDotH = saturate(halfVector.z);
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const float vDotH = saturate(dot(viewDirection, halfVector));
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if (nDotL > 0.0f) {
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const float geometry = GeometrySmithIBL(nDotV, nDotL, roughness);
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const float geometryVisibility =
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geometry * vDotH /
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max(nDotH * nDotV, IBL_EPSILON);
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const float fresnel = pow(1.0f - vDotH, 5.0f);
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scale += (1.0f - fresnel) * geometryVisibility;
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bias += fresnel * geometryVisibility;
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}
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}
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return float2(scale, bias) / float(sampleCount);
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}
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float2 PSBrdfLut(VSOutput input) : SV_TARGET {
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const float nDotV = clamp(input.uv.x, 0.001f, 1.0f);
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const float roughness = clamp(input.uv.y, 0.001f, 1.0f);
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const uint sampleCount = max(gBakeUIntParams.y, 1u);
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return IntegrateBrdf(nDotV, roughness, sampleCount);
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}
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