将立体角转换为球坐标
',4)),Q("mjx-container",i,[(t(),a("svg",L,T[8]||(T[8]=[m('代码:
vec3 irradiance = vec3(0.0);
// tangent space calculation from origin point(x'=up, y'=N, z'=left)(left-hand)
vec3 up = vec3(0.0, 1.0, 0.0); //x'
vec3 left = cross(up, N); //z'
up = cross(N, left); //x'
float sampleDelta = 0.025;
float nrSamples = 0.0;
for(float phi = 0.0; phi < 2.0 * PI; phi += sampleDelta)
{
for(float theta = 0.0; theta < 0.5 * PI; theta += sampleDelta)
{
float cosTheta = cos(theta);
float sinTheta = sin(theta);
// spherical to cartesian (in tangent space)
vec3 tangentSample = vec3(cos(phi) * sinTheta, cosTheta, sin(phi) * sinTheta);
// tangent space to world
vec3 sampleVec = tangentSample.x * up + tangentSample.y * N + tangentSample.z * left;
irradiance += texture(environmentMap, sampleVec).rgb * cosTheta * sinTheta;
nrSamples++;
}
}
irradiance = PI * irradiance * float(nrSamples);
使用蒙特卡洛采样估算积分
`,4)),Q("mjx-container",f,[(t(),a("svg",Z,T[12]||(T[12]=[m('vec3 irradiance = vec3(0.0);
vec3 up = vec3(0.0, 1.0, 0.0); //x'
vec3 left = cross(up, N); //z'
up = cross(N, left); //x'
for(uint i=0; i<sampleCounts; i++)
{
//http://holger.dammertz.org/stuff/notes_HammersleyOnHemisphere.html
vec2 uv = Hammersley(i, totalCounts);
// tangent space sample point
float phi = uv.y * 2.0 * PI;
float cosTheta = 1.0 - uv.x;
float sinTheta = sqrt(1-cosTheta*cosTheta);
vec3 tangentSample = vec3(cos(phi) * sinTheta, cosTheta, sin(phi) * sinTheta);
// tangent space to world
vec3 sampleVec = tangentSample.x * up + tangentSample.y * N + tangentSample.z * left;
irradiance += texture2D(s_texSkybox, sampleVec).rgb * cosTheta;
}
irradiance = 2*irradiance / float(sampleCounts);