113 lines
3.2 KiB
C++
113 lines
3.2 KiB
C++
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#include <iostream>
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#include <vector>
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#include <algorithm>
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#include <cmath>
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#include <sstream>
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#include <fstream>
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#include <random>
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#include "vec.h"
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#define STB_IMAGE_WRITE_IMPLEMENTATION
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#include "stb_image_write.h"
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const int resolution = 128;
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typedef struct samplePoints {
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std::vector<Vec3f> directions;
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std::vector<float> PDFs;
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}samplePoints;
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samplePoints squareToCosineHemisphere(int sample_count){
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samplePoints samlpeList;
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const int sample_side = static_cast<int>(floor(sqrt(sample_count)));
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std::random_device rd;
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std::mt19937 gen(rd());
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std::uniform_real_distribution<> rng(0.0, 1.0);
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for (int t = 0; t < sample_side; t++) {
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for (int p = 0; p < sample_side; p++) {
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double samplex = (t + rng(gen)) / sample_side;
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double sampley = (p + rng(gen)) / sample_side;
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double theta = 0.5f * acos(1 - 2*samplex);
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double phi = 2 * M_PI * sampley;
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Vec3f wi = Vec3f(sin(theta) * cos(phi), sin(theta) * sin(phi), cos(theta));
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float pdf = wi.z / PI;
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samlpeList.directions.push_back(wi);
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samlpeList.PDFs.push_back(pdf);
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}
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}
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return samlpeList;
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}
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float DistributionGGX(Vec3f N, Vec3f H, float roughness)
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{
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float a = roughness*roughness;
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float a2 = a*a;
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float NdotH = std::max(dot(N, H), 0.0f);
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float NdotH2 = NdotH*NdotH;
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float nom = a2;
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float denom = (NdotH2 * (a2 - 1.0) + 1.0);
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denom = PI * denom * denom;
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return nom / std::max(denom, 0.0001f);
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}
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float GeometrySchlickGGX(float NdotV, float roughness) {
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float a = roughness;
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float k = (a * a) / 2.0f;
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float nom = NdotV;
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float denom = NdotV * (1.0f - k) + k;
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return nom / denom;
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}
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float GeometrySmith(float roughness, float NoV, float NoL) {
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float ggx2 = GeometrySchlickGGX(NoV, roughness);
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float ggx1 = GeometrySchlickGGX(NoL, roughness);
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return ggx1 * ggx2;
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}
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Vec3f IntegrateBRDF(Vec3f V, float roughness, float NdotV) {
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float A = 0.0;
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float B = 0.0;
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float C = 0.0;
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const int sample_count = 1024;
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Vec3f N = Vec3f(0.0, 0.0, 1.0);
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samplePoints sampleList = squareToCosineHemisphere(sample_count);
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for (int i = 0; i < sample_count; i++) {
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// TODO: To calculate (fr * ni) / p_o here
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}
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return {A / sample_count, B / sample_count, C / sample_count};
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}
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int main() {
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uint8_t data[resolution * resolution * 3];
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float step = 1.0 / resolution;
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for (int i = 0; i < resolution; i++) {
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for (int j = 0; j < resolution; j++) {
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float roughness = step * (static_cast<float>(i) + 0.5f);
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float NdotV = step * (static_cast<float>(j) + 0.5f);
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Vec3f V = Vec3f(std::sqrt(1.f - NdotV * NdotV), 0.f, NdotV);
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Vec3f irr = IntegrateBRDF(V, roughness, NdotV);
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data[(i * resolution + j) * 3 + 0] = uint8_t(irr.x * 255.0);
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data[(i * resolution + j) * 3 + 1] = uint8_t(irr.y * 255.0);
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data[(i * resolution + j) * 3 + 2] = uint8_t(irr.z * 255.0);
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}
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}
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stbi_flip_vertically_on_write(true);
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stbi_write_png("GGX_E_MC_LUT.png", resolution, resolution, 3, data, resolution * 3);
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std::cout << "Finished precomputed!" << std::endl;
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return 0;
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}
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