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88 lines
3.1 KiB
GLSL
88 lines
3.1 KiB
GLSL
#ifndef IBL_COMMON_GLSL
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#define IBL_COMMON_GLSL
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/*
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** Physical based render code, develop by engineer: qiutanguu.
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*/
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#include "LightingCommon.glsl"
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// https://www.mathematik.uni-marburg.de/~thormae/lectures/graphics1/code/ImportanceSampling/importance_sampling_notes.pdf
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// Based on http://blog.selfshadow.com/publications/s2013-shading-course/karis/s2013_pbs_epic_slides.pdf
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// https://bruop.github.io/ibl/
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vec3 importanceSampleGGX(vec2 Xi, float alphaRoughness, vec3 normal)
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{
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// Maps a 2D point to a hemisphere with spread based on roughness.
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float alpha = alphaRoughness * alphaRoughness;
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// Sample in spherical coordinates.
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float phi = 2.0 * kPI * Xi.x;
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float cosTheta = sqrt((1.0 - Xi.y) / (1.0 + (alpha * alpha - 1.0) * Xi.y));
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float sinTheta = sqrt(1.0 - cosTheta * cosTheta);
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// Construct tangent space sample vector.
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vec3 H = vec3(sinTheta * cos(phi), sinTheta * sin(phi), cosTheta);
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// Tangent space
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vec3 up = abs(normal.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(up, normal));
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vec3 tangentY = normalize(cross(normal, tangentX));
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// Convert to world Space
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return normalize(tangentX * H.x + tangentY * H.y + normal * H.z);
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}
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// http://jcgt.org/published/0007/04/01/paper.pdf by Eric Heitz
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// Input Ve: view direction
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// Input alpha_x, alpha_y: roughness parameters
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// Input U1, U2: uniform random numbers
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// Output Ne: normal sampled with PDF D_Ve(Ne) = G1(Ve) * max(0, dot(Ve, Ne)) * D(Ne) / Ve.z
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vec3 importanceSampleGGXVNDF(vec3 Ve, float alpha_x, float alpha_y, float U1, float U2)
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{
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// Section 3.2: transforming the view direction to the hemisphere configuration
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vec3 Vh = normalize(vec3(alpha_x * Ve.x, alpha_y * Ve.y, Ve.z));
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// Section 4.1: orthonormal basis (with special case if cross product is zero)
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float lensq = Vh.x * Vh.x + Vh.y * Vh.y;
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vec3 T1 = lensq > 0 ? vec3(-Vh.y, Vh.x, 0) * inversesqrt(lensq) : vec3(1, 0, 0);
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vec3 T2 = cross(Vh, T1);
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// Section 4.2: parameterization of the projected area
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float r = sqrt(U1);
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float phi = 2.0 * kPI * U2;
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float t1 = r * cos(phi);
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float t2 = r * sin(phi);
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float s = 0.5 * (1.0 + Vh.z);
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t2 = (1.0 - s) * sqrt(1.0 - t1 * t1) + s * t2;
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// Section 4.3: reprojection onto hemisphere
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vec3 Nh = t1 * T1 + t2 * T2 + sqrt(max(0.0, 1.0 - t1 * t1 - t2 * t2)) * Vh;
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// Section 3.4: transforming the normal back to the ellipsoid configuration
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vec3 Ne = normalize(vec3(alpha_x * Nh.x, alpha_y * Nh.y, max(0.0, Nh.z)));
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return Ne;
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}
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// Importance sample use cosine weight.
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vec3 importanceSampleCosine(vec2 xi, vec3 N)
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{
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float phi = 2.f * kPI * xi.y;
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float cosTheta = sqrt(xi.x);
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float sinTheta = sqrt(1 - xi.x);
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vec3 sampleHemisphere = vec3(cos(phi) * sinTheta, sin(phi) * sinTheta, cosTheta);
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//orient sample into world space
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vec3 up = abs(N.z) < 0.999 ? vec3(0.f, 0.f, 1.f) : vec3(1.f, 0.f, 0.f);
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vec3 tangent = normalize(cross(up, N));
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vec3 bitangent = cross(N, tangent);
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vec3 sampleWorld = vec3(0);
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sampleWorld += sampleHemisphere.x * tangent;
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sampleWorld += sampleHemisphere.y * bitangent;
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sampleWorld += sampleHemisphere.z * N;
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return sampleWorld;
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}
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#endif |