71 lines
2.0 KiB
GLSL
71 lines
2.0 KiB
GLSL
precision highp float;
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in vec3 v_textureCoordinates;
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uniform float u_roughness;
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uniform samplerCube u_radianceTexture;
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uniform vec3 u_faceDirection;
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float vdcRadicalInverse(int i)
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{
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float r;
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float base = 2.0;
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float value = 0.0;
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float invBase = 1.0 / base;
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float invBi = invBase;
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for (int x = 0; x < 100; x++)
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{
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if (i <= 0)
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{
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break;
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}
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r = mod(float(i), base);
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value += r * invBi;
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invBi *= invBase;
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i = int(float(i) * invBase);
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}
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return value;
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}
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vec2 hammersley2D(int i, int N)
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{
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return vec2(float(i) / float(N), vdcRadicalInverse(i));
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}
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vec3 importanceSampleGGX(vec2 xi, float alphaRoughness, vec3 N)
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{
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float alphaRoughnessSquared = alphaRoughness * alphaRoughness;
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float phi = czm_twoPi * xi.x;
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float cosTheta = sqrt((1.0 - xi.y) / (1.0 + (alphaRoughnessSquared - 1.0) * xi.y));
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float sinTheta = sqrt(1.0 - cosTheta * cosTheta);
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vec3 H = vec3(sinTheta * cos(phi), sinTheta * sin(phi), cosTheta);
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vec3 upVector = abs(N.z) < 0.999 ? vec3(0.0, 0.0, 1.0) : vec3(1.0, 0.0, 0.0);
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vec3 tangentX = normalize(cross(upVector, N));
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vec3 tangentY = cross(N, tangentX);
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return tangentX * H.x + tangentY * H.y + N * H.z;
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}
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// Sample count is relatively low for the sake of performance, but should still be enough to prevent artifacting in lower roughnesses
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const int samples = 128;
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void main() {
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vec3 normal = u_faceDirection;
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vec3 V = normalize(v_textureCoordinates);
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float roughness = u_roughness;
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vec4 color = vec4(0.0);
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float weight = 0.0;
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for (int i = 0; i < samples; ++i) {
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vec2 xi = hammersley2D(i, samples);
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vec3 H = importanceSampleGGX(xi, roughness, V);
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vec3 L = 2.0 * dot(V, H) * H - V; // reflected vector
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float NdotL = max(dot(V, L), 0.0);
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if (NdotL > 0.0) {
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color += vec4(czm_textureCube(u_radianceTexture, L).rgb, 1.0) * NdotL;
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weight += NdotL;
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}
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}
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out_FragColor = color / weight;
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}
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