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网上如何建网站卖量具,申请免费网站主页空间,2017如何免费制作网站,黑糖主题2.0wordpress再回顾下镜面部分的分割求和近似法现在关注第二部分最后可化为也就是说，这两部分积分可以获得F0的系数和F0的偏差。这两个值可以存储到BRDF积分贴图的RG部分。void main() { vec2 integratedBRDF IntegrateBRDF(TexCoords.x, TexCoords.y); FragColor …

再回顾下镜面部分的分割求和近似法
在这里插入图片描述
现在关注第二部分

最后可化为

也就是说，这两部分积分可以获得F0的系数和F0的偏差。

这两个值可以存储到BRDF积分贴图的RG部分。

void main()
{
vec2 integratedBRDF = IntegrateBRDF(TexCoords.x, TexCoords.y);
FragColor = integratedBRDF;
}
再看函数vec2 IntegrateBRDF(float NdotV, float roughness) ，可知积分贴图的横坐标是NotV,纵坐标是粗糙度。
查看这个RG是如何计算的。

		循环采样后A /= float(SAMPLE_COUNT);	B /= float(SAMPLE_COUNT);	return vec2(A, B);			即A,B分别是F0和系数和F0的偏差，也就是积分贴图的RG部分。结合公式

在这里插入图片描述
在对每个采样向量中，
float Fc = pow(1.0 - VdotH, 5.0);
A += (1.0 - Fc) * G_Vis;
B += Fc * G_Vis;

	继续向下float G = GeometrySmith(N, V, L, roughness);	float G_Vis = (G * VdotH) / (NdotH * NdotV);	可知，使用BRDF的几何函数处理了采样向量。继续向下vec2 Xi = Hammersley(i, SAMPLE_COUNT);

vec3 H = ImportanceSampleGGX(Xi, N, roughness);
vec3 L = normalize(2.0 * dot(V, H) * H - V);
类似于预过滤环境贴图，也是通过低差异序列进行重要性采样获取采样向量。

在c++部分。
设置brdf积分贴图为512x512,纹理设置为GL_RG
texture->setSourceFormat(GL_RG);
运行结果如下：
在这里插入图片描述
代码如下：
#include <osg/TextureCubeMap>
#include <osg/TexGen>
#include <osg/TexEnvCombine>
#include <osgUtil/ReflectionMapGenerator>
#include <osgDB/ReadFile>
#include <osgViewer/Viewer>
#include <osg/NodeVisitor>
#include <osg/ShapeDrawable>
#include <osg/Texture2D>
#include <osgDB/WriteFile>
static const char * vertexShader =
{
“in vec3 aPos;\n”
“in vec2 texcoord;”
“varying vec2 TexCoords;\n”
“void main(void)\n”
“{\n”
“TexCoords = texcoord;\n”
“gl_Position = ftransform();\n”
//“gl_Position = view * view * vec4(aPos,1.0);”
“}\n”
};

static const char psShader =
{
“#version 330 core \n”
“out vec2 FragColor; \n”
“in vec2 TexCoords; \n”
" \n"
“const float PI = 3.14159265359; \n”
“// ---------------------------------------------------------------------------- \n”
“// http://holger.dammertz.org/stuff/notes_HammersleyOnHemisphere.html \n”
“// efficient VanDerCorpus calculation. \n”
“float RadicalInverse_VdC(uint bits) \n”
“{ \n”
" bits = (bits << 16u) | (bits >> 16u); \n"
" bits = ((bits & 0x55555555u) << 1u) | ((bits & 0xAAAAAAAAu) >> 1u); \n"
" bits = ((bits & 0x33333333u) << 2u) | ((bits & 0xCCCCCCCCu) >> 2u); \n"
" bits = ((bits & 0x0F0F0F0Fu) << 4u) | ((bits & 0xF0F0F0F0u) >> 4u); \n"
" bits = ((bits & 0x00FF00FFu) << 8u) | ((bits & 0xFF00FF00u) >> 8u); \n"
" return float(bits) * 2.3283064365386963e-10; // / 0x100000000 \n"
“} \n”
“// ---------------------------------------------------------------------------- \n”
“vec2 Hammersley(uint i, uint N) \n”
“{ \n”
" return vec2(float(i) / float(N), RadicalInverse_VdC(i)); \n"
“} \n”
“// ---------------------------------------------------------------------------- \n”
“vec3 ImportanceSampleGGX(vec2 Xi, vec3 N, float roughness) \n”
“{ \n”
" float a = roughnessroughness; \n"
" \n"
" float phi = 2.0 * PI * Xi.x; \n"
" float cosTheta = sqrt((1.0 - Xi.y) / (1.0 + (aa - 1.0) * Xi.y)); \n"
" float sinTheta = sqrt(1.0 - cosThetacosTheta); \n"
" \n"
" // from spherical coordinates to cartesian coordinates - halfway vector \n"
" vec3 H; \n"
" H.x = cos(phi) * sinTheta; \n"
" H.y = sin(phi) * sinTheta; \n"
" H.z = cosTheta; \n"
" \n"
" // from tangent-space H vector to world-space sample vector \n"
" vec3 up = abs(N.z) < 0.999 ? vec3(0.0, 0.0, 1.0) : vec3(1.0, 0.0, 0.0); \n"
" vec3 tangent = normalize(cross(up, N)); \n"
" vec3 bitangent = cross(N, tangent); \n"
" \n"
" vec3 sampleVec = tangent * H.x + bitangent * H.y + N * H.z; \n"
" return normalize(sampleVec); \n"
“} \n”
“// ---------------------------------------------------------------------------- \n”
“float GeometrySchlickGGX(float NdotV, float roughness) \n”
“{ \n”
" // note that we use a different k for IBL \n"
" float a = roughness; \n"
" float k = (a * a) / 2.0; \n"
" \n"
" float nom = NdotV; \n"
" float denom = NdotV * (1.0 - k) + k; \n"
" \n"
" return nom / denom; \n"
“} \n”
“// ---------------------------------------------------------------------------- \n”
“float GeometrySmith(vec3 N, vec3 V, vec3 L, float roughness) \n”
“{ \n”
" float NdotV = max(dot(N, V), 0.0); \n"
" float NdotL = max(dot(N, L), 0.0); \n"
" float ggx2 = GeometrySchlickGGX(NdotV, roughness); \n"
" float ggx1 = GeometrySchlickGGX(NdotL, roughness); \n"
" \n"
" return ggx1 * ggx2; \n"
“} \n”
“// ---------------------------------------------------------------------------- \n”
“vec2 IntegrateBRDF(float NdotV, float roughness) \n”
“{ \n”
" vec3 V; \n"
" V.x = sqrt(1.0 - NdotV*NdotV); \n"
" V.y = 0.0; \n"
" V.z = NdotV; \n"
" \n"
" float A = 0.0; \n"
" float B = 0.0; \n"
" \n"
" vec3 N = vec3(0.0, 0.0, 1.0); \n"
" \n"
" const uint SAMPLE_COUNT = 1024u; \n"
" for (uint i = 0u; i < SAMPLE_COUNT; ++i) \n"
" { \n"
" // generates a sample vector that’s biased towards the \n"
" // preferred alignment direction (importance sampling). \n"
" vec2 Xi = Hammersley(i, SAMPLE_COUNT); \n"
" vec3 H = ImportanceSampleGGX(Xi, N, roughness); \n"
" vec3 L = normalize(2.0 * dot(V, H) * H - V); \n"
" \n"
" float NdotL = max(L.z, 0.0); \n"
" float NdotH = max(H.z, 0.0); \n"
" float VdotH = max(dot(V, H), 0.0); \n"
" \n"
" if (NdotL > 0.0) \n"
" { \n"
" float G = GeometrySmith(N, V, L, roughness); \n"
" float G_Vis = (G * VdotH) / (NdotH * NdotV); \n"
" float Fc = pow(1.0 - VdotH, 5.0); \n"
" \n"
" A += (1.0 - Fc) * G_Vis; \n"
" B += Fc * G_Vis; \n"
" } \n"
" } \n"
" A /= float(SAMPLE_COUNT); \n"
" B /= float(SAMPLE_COUNT); \n"
" return vec2(A, B); \n"
“} \n”
“// ---------------------------------------------------------------------------- \n”
“void main() \n”
“{ \n”
" vec2 integratedBRDF = IntegrateBRDF(TexCoords.x, TexCoords.y); \n"
" FragColor = integratedBRDF; \n"
“} \n”
};

int main()
{
int imageWidth = 512;
int imageHeight = 512;
osg::ref_ptrosg::Vec3Array vertices = new osg::Vec3Array;

vertices->push_back(osg::Vec3(-imageWidth, 0.0f, -imageHeight));
vertices->push_back(osg::Vec3(imageWidth, 0.0f, -imageHeight));
vertices->push_back(osg::Vec3(imageWidth, 0.0f, imageHeight));
vertices->push_back(osg::Vec3(-imageWidth, 0.0f, imageHeight));
osg::ref_ptr<osg::Vec3Array> normals = new osg::Vec3Array;
normals->push_back(osg::Vec3(0.0f, -1.0f, 0.0f));
osg::ref_ptr<osg::Vec2Array> texcoords = new osg::Vec2Array;
texcoords->push_back(osg::Vec2(0.0f, 0.0f));
texcoords->push_back(osg::Vec2(1.0f, 0.0f));
texcoords->push_back(osg::Vec2(1.0f, 1.0f));
texcoords->push_back(osg::Vec2(0.0f, 1.0f));
osg::ref_ptr<osg::Geometry> quad = new osg::Geometry;
quad->setVertexArray(vertices.get());quad->setNormalArray(normals.get());
quad->setNormalBinding(osg::Geometry::BIND_OVERALL);
quad->setTexCoordArray(0, texcoords.get());
quad->addPrimitiveSet(new osg::DrawArrays(GL_QUADS, 0, 4));quad->setVertexAttribArray(1, vertices, osg::Array::BIND_PER_VERTEX);
quad->setVertexAttribArray(2, texcoords, osg::Array::BIND_PER_VERTEX);
osg::ref_ptr<osg::Texture2D> texture = new osg::Texture2D;
texture->setSourceFormat(GL_RG);
texture->setFilter(osg::Texture2D::MIN_FILTER, osg::Texture2D::LINEAR);
texture->setFilter(osg::Texture2D::MAG_FILTER, osg::Texture2D::LINEAR);
texture->setWrap(osg::Texture::WRAP_S, osg::Texture::CLAMP_TO_EDGE);
texture->setWrap(osg::Texture::WRAP_T, osg::Texture::CLAMP_TO_EDGE);
osg::ref_ptr<osg::Geode> geode = new osg::Geode;
geode->addDrawable(quad.get());
osg::ref_ptr<osg::StateSet> stateset = geode->getOrCreateStateSet();
stateset->setTextureAttributeAndModes(0, texture.get());//shaderosg::ref_ptr<osg::Shader> vs1 = new osg::Shader(osg::Shader::VERTEX, vertexShader);
osg::ref_ptr<osg::Shader> ps1 = new osg::Shader(osg::Shader::FRAGMENT, psShader);
osg::ref_ptr<osg::Program> program1 = new osg::Program;
program1->addShader(vs1);
program1->addShader(ps1);
program1->addBindAttribLocation("aPos", 1);
program1->addBindAttribLocation("texcoord", 2);osg::ref_ptr<osg::Uniform> tex0Uniform = new osg::Uniform("tex0", 0);
stateset->addUniform(tex0Uniform);
stateset->setAttribute(program1, osg::StateAttribute::ON);//osgDB::writeImageFile(*image, strBRDFLUTImageName);
osgViewer::Viewer viewer;
viewer.setSceneData(geode.get());bool bPrinted = false;
return viewer.run();

}

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