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Merge pull request #107168 from Rudolph-B/Issue-102300

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Fix SH lightmap coefficients for direct lights
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Rémi Verschelde 2025-06-09 00:44:59 +02:00
commit 36d7a87cc8
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1 changed files with 24 additions and 8 deletions
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32
modules/lightmapper_rd/lm_compute.glsl
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@ -861,16 +861,32 @@ void main() {
light_for_texture += light;
#ifdef USE_SH_LIGHTMAPS
// These coefficients include the factored out SH evaluation, diffuse convolution, and final application, as well as the BRDF 1/PI and the spherical monte carlo factor.
// LO: 1/(2*sqrtPI) * 1/(2*sqrtPI) * PI * PI * 1/PI = 0.25
// L1: sqrt(3/(4*pi)) * sqrt(3/(4*pi)) * (PI*2/3) * (2 * PI) * 1/PI = 1.0
// Note: This only works because we aren't scaling, rotating, or combing harmonics, we are just directing applying them in the shader.
// For L0, light needs to be attenuated by dot(normal, light_dir) else it is oversaturated when sampled later.
// For L1, light can't be attenuated by dot(normal, light_dir) since when sampling later, the dot product is done.
// The output of trace_direct_light() is already attenuated by dot(normal, light_dir).
// So L0 and L1 has the following relationship: L1 = L0 / dot(normal, light_dir).
// For L1 packing to work, there needs to be a defined ratio (4) between L0 and L1 values.
// This ratio is achieved with two coefficients c_l0 and c_l1, and ensuring that
// 4 = (c_l0 * LO) / (c_l1 * L1)
// For direct lights to look right, its effective "energy" needs to be 1 since it is not being integrated
// unlike indirect lighting.
// This binds c_l0 and c_l1 to the following relationship: 1 = c_l0 + c_l1
float attenuation = dot(normal, light_dir);
if (attenuation <= 0.0001) {
continue;
}
float c_l0 = 1 / (1 + 4 * attenuation);
float c_l1 = 1 - c_l0;
float c[4] = float[](
0.25, //l0
light_dir.y, //l1n1
light_dir.z, //l1n0
light_dir.x //l1p1
c_l0, //l0
c_l1 / attenuation * light_dir.y, //l1n1
c_l1 / attenuation * light_dir.z, //l1n0
c_l1 / attenuation * light_dir.x //l1p1
);
for (uint j = 0; j < 4; j++) {