# all files / src/util/shader/ integrateBRDF.glsl.js

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     export default "#define SAMPLE_NUMBER 1024\n#define PI 3.14159265358979\nuniform sampler2D normalDistribution;\nuniform vec2 viewportSize : [512, 256];\nconst vec3 N = vec3(0.0, 0.0, 1.0);\nconst float fSampleNumber = float(SAMPLE_NUMBER);\nvec3 importanceSampleNormal(float i, float roughness, vec3 N) {\n    vec3 H = texture2D(normalDistribution, vec2(roughness, i)).rgb;\n    vec3 upVector = abs(N.z) < 0.999 ? vec3(0.0, 0.0, 1.0) : vec3(1.0, 0.0, 0.0);\n    vec3 tangentX = normalize(cross(upVector, N));\n    vec3 tangentY = cross(N, tangentX);\n    return tangentX * H.x + tangentY * H.y + N * H.z;\n}\nfloat G_Smith(float roughness, float NoV, float NoL) {\n    float k = roughness * roughness / 2.0;\n    float G1V = NoV / (NoV * (1.0 - k) + k);\n    float G1L = NoL / (NoL * (1.0 - k) + k);\n    return G1L * G1V;\n}\nvoid main() {\n    vec2 uv = gl_FragCoord.xy / viewportSize;\n    float NoV = uv.x;\n    float roughness = uv.y;\n    vec3 V;\n    V.x = sqrt(1.0 - NoV * NoV);\n    V.y = 0.0;\n    V.z = NoV;\n    float A = 0.0;\n    float B = 0.0;\n    for (int i = 0; i < SAMPLE_NUMBER; i++) {\n        vec3 H = importanceSampleNormal(float(i) / fSampleNumber, roughness, N);\n        vec3 L = reflect(-V, H);\n        float NoL = clamp(L.z, 0.0, 1.0);\n        float NoH = clamp(H.z, 0.0, 1.0);\n        float VoH = clamp(dot(V, H), 0.0, 1.0);\n        if (NoL > 0.0) {\n            float G = G_Smith(roughness, NoV, NoL);\n            float G_Vis = G * VoH / (NoH * NoV);\n            float Fc = pow(1.0 - VoH, 5.0);\n            A += (1.0 - Fc) * G_Vis;\n            B += Fc * G_Vis;\n        }\n    }\n    gl_FragColor = vec4(vec2(A, B) / fSampleNumber, 0.0, 1.0);\n}\n";