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Respect physicallyCorrectLights on lightmaps in MeshBasicMaterial #23197

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Respect physicallyCorrectLights on lightmaps in MeshBasicMaterial #23197

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13 changes: 11 additions & 2 deletions src/renderers/shaders/ShaderLib/meshbasic.glsl.js
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Original file line number Diff line number Diff line change
Expand Up @@ -86,8 +86,17 @@ void main() {
// accumulation (baked indirect lighting only)
#ifdef USE_LIGHTMAP

vec4 lightMapTexel= texture2D( lightMap, vUv2 );
reflectedLight.indirectDiffuse += lightMapTexel.rgb * lightMapIntensity;
vec4 lightMapTexel = texture2D( lightMap, vUv2 );
vec3 lightMapIrradiance = lightMapTexel.rgb * lightMapIntensity;

// Lightmaps are the only source of "light" for basic materials, respect them being "phsyically correct"
#ifdef PHYSICALLY_CORRECT_LIGHTS
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Note that in lightmap_fragment.glsl.js we have the inverse behavior, multiplying the value by PI if PHYSICALLY_CORRECT_LIGHTS is not defined. This is to cancel out the effect of BRDF_Lambert(diffuseColor) which is applied by default in most other materials (which multiplies the diffuseColro by RECIPROCAL_PI). MeshBasicMaterial does not apply BRDF_Lambert to the diffuseColor so we need to do the inverse for the lightmap to be "physically correct"

We probably do not want to change how a MeshBasicMaterial with no lightmap behaves so we instead apply this here, only to lightmaps, and only when PHYSICALLY_CORRECT_LIGHTS is defined. We could change the surrounding code a bit such that we could #include <lightmpmap_fragment> unchanged but it would slightly complicate the common case of a MeshBasicMaterial with no lightmap.


lightMapIrradiance *= RECIPROCAL_PI;

#endif

reflectedLight.indirectDiffuse += lightMapIrradiance;

#else

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