Correct diffuse component for image-based lighting

Apps/Sandcastle/gallery/Image-Based Lighting.html

@@ -65,63 +65,63 @@
           );
         }
 
-        const environmentMapURL =
-          "https://cesium.com/public/SandcastleSampleData/kiara_6_afternoon_2k_ibl.ktx2";
         const modelURL = "../../SampleData/models/Pawns/Pawns.glb";
 
         // This environment map was processed using Khronos's glTF IBL Sampler. To process your own:
         // 1 - Download and build the Khronos glTF IBL Sampler (https://github.com/KhronosGroup/glTF-IBL-Sampler).
         // 2 - Run `cli -inputPath /path/to/image.hdr -outCubeMap /path/to/output.ktx2`. Run `cli -h` for all options.
+        const environmentMapURL =
+          "https://cesium.com/public/SandcastleSampleData/kiara_6_afternoon_2k_ibl.ktx2";
 
         // To generate the spherical harmonic coefficients below, use Google's Filament project:
         // 1 - Download the Filament release (https://github.com/google/filament/releases).
-        // 2 - Run `cmgen --type=ktx --deploy=/path/to/output /path/to/image.hdr`. Other formats are also supported. Run `cmgen --help` for all options.
+        // 2 - Run `cmgen --no-mirror --type=ktx --deploy=/path/to/output /path/to/image.hdr`.
+        //     Other formats are also supported. Run `cmgen --help` for all options.
         // 3 - Take the generated coefficients and load them in CesiumJS as shown below.
-
         const L00 = new Cesium.Cartesian3(
-          1.234709620475769,
-          1.221461296081543,
-          1.273156881332397
+          1.234897375106812,
+          1.221635103225708,
+          1.273374080657959
         );
         const L1_1 = new Cesium.Cartesian3(
-          1.135921120643616,
-          1.171217799186707,
-          1.287644743919373
+          1.136140108108521,
+          1.171419978141785,
+          1.287894368171692
         );
         const L10 = new Cesium.Cartesian3(
-          1.245193719863892,
-          1.245591878890991,
-          1.282818794250488
+          1.245410919189453,
+          1.245791077613831,
+          1.283067107200623
         );
         const L11 = new Cesium.Cartesian3(
-          -1.106930732727051,
-          -1.112522482872009,
-          -1.153198838233948
+          1.107124328613281,
+          1.112697005271912,
+          1.153419137001038
         );
         const L2_2 = new Cesium.Cartesian3(
-          -1.086226940155029,
-          -1.079731941223145,
-          -1.101912498474121
+          1.08641505241394,
+          1.079904079437256,
+          1.10212504863739
         );
         const L2_1 = new Cesium.Cartesian3(
-          1.189834713935852,
-          1.185906887054443,
-          1.214385271072388
+          1.190043210983276,
+          1.186099290847778,
+          1.214627981185913
         );
         const L20 = new Cesium.Cartesian3(
-          0.01778045296669,
-          0.02013735473156,
-          0.025313569232821
+          0.017783647403121,
+          0.020140396431088,
+          0.025317270308733
         );
         const L21 = new Cesium.Cartesian3(
-          -1.086826920509338,
-          -1.084611177444458,
-          -1.111204028129578
+          1.087014317512512,
+          1.084779262542725,
+          1.111417651176453
         );
         const L22 = new Cesium.Cartesian3(
-          -0.05241484940052,
-          -0.048303380608559,
-          -0.041960217058659
+          -0.052426788955927,
+          -0.048315055668354,
+          -0.041973855346441
         );
         const coefficients = [L00, L1_1, L10, L11, L2_2, L2_1, L20, L21, L22];
 

Apps/Sandcastle/gallery/glTF PBR Extensions.html

@@ -79,52 +79,53 @@
 
         // To generate the spherical harmonic coefficients below, use Google's Filament project:
         // 1 - Download the Filament release (https://github.com/google/filament/releases).
-        // 2 - Run `cmgen --type=ktx --deploy=/path/to/output /path/to/image.hdr`. Other formats are also supported. Run `cmgen --help` for all options.
+        // 2 - Run `cmgen --no-mirror --type=ktx --deploy=/path/to/output /path/to/image.hdr`.
+        //     Other formats are also supported. Run `cmgen --help` for all options.
         // 3 - Take the generated coefficients and load them in CesiumJS as shown below.
         const L00 = new Cesium.Cartesian3(
-          1.234709620475769,
-          1.221461296081543,
-          1.273156881332397
+          1.234897375106812,
+          1.221635103225708,
+          1.273374080657959
         );
         const L1_1 = new Cesium.Cartesian3(
-          1.135921120643616,
-          1.171217799186707,
-          1.287644743919373
+          1.136140108108521,
+          1.171419978141785,
+          1.287894368171692
         );
         const L10 = new Cesium.Cartesian3(
-          1.245193719863892,
-          1.245591878890991,
-          1.282818794250488
+          1.245410919189453,
+          1.245791077613831,
+          1.283067107200623
         );
         const L11 = new Cesium.Cartesian3(
-          -1.106930732727051,
-          -1.112522482872009,
-          -1.153198838233948
+          1.107124328613281,
+          1.112697005271912,
+          1.153419137001038
         );
         const L2_2 = new Cesium.Cartesian3(
-          -1.086226940155029,
-          -1.079731941223145,
-          -1.101912498474121
+          1.08641505241394,
+          1.079904079437256,
+          1.10212504863739
         );
         const L2_1 = new Cesium.Cartesian3(
-          1.189834713935852,
-          1.185906887054443,
-          1.214385271072388
+          1.190043210983276,
+          1.186099290847778,
+          1.214627981185913
         );
         const L20 = new Cesium.Cartesian3(
-          0.01778045296669,
-          0.02013735473156,
-          0.025313569232821
+          0.017783647403121,
+          0.020140396431088,
+          0.025317270308733
         );
         const L21 = new Cesium.Cartesian3(
-          -1.086826920509338,
-          -1.084611177444458,
-          -1.111204028129578
+          1.087014317512512,
+          1.084779262542725,
+          1.111417651176453
         );
         const L22 = new Cesium.Cartesian3(
-          -0.05241484940052,
-          -0.048303380608559,
-          -0.041960217058659
+          -0.052426788955927,
+          -0.048315055668354,
+          -0.041973855346441
         );
         const coefficients = [L00, L1_1, L10, L11, L2_2, L2_1, L20, L21, L22];
 

CHANGES.md

@@ -8,6 +8,7 @@
 
 - Updated geometric self-shadowing function to improve direct lighting on models using physically-based rendering. [#12063](https://github.com/CesiumGS/cesium/pull/12063)
 - Fixed environment map LOD selection in image-based lighting. [#12070](https://github.com/CesiumGS/cesium/pull/12070)
+- Corrected calculation of diffuse component in image-based lighting. [#12082](https://github.com/CesiumGS/cesium/pull/12082)
 
 ### 1.119 - 2024-07-01
 

packages/engine/Source/Scene/ImageBasedLighting.js

@@ -186,8 +186,8 @@ Object.defineProperties(ImageBasedLighting.prototype, {
    * </p>
    *
    * These values can be obtained by preprocessing the environment map using the <code>cmgen</code> tool of
-   * {@link https://github.com/google/filament/releases|Google's Filament project}. This will also generate a KTX file that can be
-   * supplied to {@link Model#specularEnvironmentMaps}.
+   * {@link https://github.com/google/filament/releases|Google's Filament project}.
+   * Be sure to use the <code>--no-mirror</code> option in <code>cmgen</code>.
    *
    * @memberof ImageBasedLighting.prototype
    *

packages/engine/Source/Shaders/Model/ImageBasedLightingStageFS.glsl

@@ -121,7 +121,7 @@ float getSunLuminance(vec3 positionWC, vec3 normalEC, vec3 lightDirectionEC)
 ) {
     vec3 viewDirectionEC = -normalize(positionEC);
     vec3 positionWC = vec3(czm_inverseView * vec4(positionEC, 1.0));
-    vec3 reflectionWC = normalize(czm_inverseViewRotation * normalize(reflect(viewDirectionEC, normalEC)));
+    vec3 reflectionWC = normalize(czm_inverseViewRotation * reflect(viewDirectionEC, normalEC));
     vec3 skyMetrics = getProceduralSkyMetrics(positionWC, reflectionWC);
 
     float roughness = material.roughness;
@@ -202,34 +202,33 @@ vec3 textureIBL(
     vec3 lightDirectionEC,
     czm_modelMaterial material
 ) {
-    // Find the direction in which to sample the environment map
-    vec3 cubeDir = normalize(model_iblReferenceFrameMatrix * normalize(reflect(-viewDirectionEC, normalEC)));
-
     #ifdef DIFFUSE_IBL
-        vec3 diffuseContribution = computeDiffuseIBL(cubeDir) * material.diffuse;
+        vec3 normalMC = normalize(model_iblReferenceFrameMatrix * normalEC);
+        vec3 diffuseContribution = computeDiffuseIBL(normalMC) * material.diffuse;
     #else
         vec3 diffuseContribution = vec3(0.0); 
     #endif
 
-    float roughness = material.roughness;
-
     #ifdef USE_ANISOTROPY
-        // Update environment map sampling direction to account for anisotropic distortion of specular reflection
+        // Bend normal to account for anisotropic distortion of specular reflection
         vec3 anisotropyDirection = material.anisotropicB;
         vec3 anisotropicTangent = cross(anisotropyDirection, viewDirectionEC);
         vec3 anisotropicNormal = cross(anisotropicTangent, anisotropyDirection);
-        float bendFactor = 1.0 - material.anisotropyStrength * (1.0 - roughness);
+        float bendFactor = 1.0 - material.anisotropyStrength * (1.0 - material.roughness);
         float bendFactorPow4 = bendFactor * bendFactor * bendFactor * bendFactor;
         vec3 bentNormal = normalize(mix(anisotropicNormal, normalEC, bendFactorPow4));
-        cubeDir = normalize(model_iblReferenceFrameMatrix * normalize(reflect(-viewDirectionEC, bentNormal)));
+        vec3 reflectEC = reflect(-viewDirectionEC, bentNormal);
+    #else
+        vec3 reflectEC = reflect(-viewDirectionEC, normalEC);
     #endif
 
     #ifdef SPECULAR_IBL
+        vec3 reflectMC = normalize(model_iblReferenceFrameMatrix * reflectEC);
         float NdotV = abs(dot(normalEC, viewDirectionEC)) + 0.001;
         vec3 halfwayDirectionEC = normalize(viewDirectionEC + lightDirectionEC);
         float VdotH = clamp(dot(viewDirectionEC, halfwayDirectionEC), 0.0, 1.0);
         vec3 f0 = material.specular;
-        vec3 specularContribution = computeSpecularIBL(cubeDir, NdotV, VdotH, f0, roughness);
+        vec3 specularContribution = computeSpecularIBL(reflectMC, NdotV, VdotH, f0, material.roughness);
     #else
         vec3 specularContribution = vec3(0.0); 
     #endif

packages/engine/Source/Shaders/Model/LightingStageFS.glsl

@@ -40,12 +40,12 @@ vec3 addClearcoatReflection(vec3 baseLayerColor, vec3 position, vec3 lightDirect
 
     #ifdef SPECULAR_IBL
         // Find the direction in which to sample the environment map
-        vec3 cubeDir = normalize(model_iblReferenceFrameMatrix * normalize(reflect(-viewDirection, normal)));
-        vec3 iblColor = computeSpecularIBL(cubeDir, NdotV, NdotV, f0, roughness);
+        vec3 reflectMC = normalize(model_iblReferenceFrameMatrix * reflect(-viewDirection, normal));
+        vec3 iblColor = computeSpecularIBL(reflectMC, NdotV, NdotV, f0, roughness);
         color += iblColor * material.occlusion;
     #elif defined(USE_IBL_LIGHTING)
         vec3 positionWC = vec3(czm_inverseView * vec4(position, 1.0));
-        vec3 reflectionWC = normalize(czm_inverseViewRotation * normalize(reflect(viewDirection, normal)));
+        vec3 reflectionWC = normalize(czm_inverseViewRotation * reflect(viewDirection, normal));
         vec3 skyMetrics = getProceduralSkyMetrics(positionWC, reflectionWC);
 
         vec3 specularIrradiance = getProceduralSpecularIrradiance(reflectionWC, skyMetrics, roughness);
@@ -57,7 +57,7 @@ vec3 addClearcoatReflection(vec3 baseLayerColor, vec3 position, vec3 lightDirect
         #endif
         float maximumComponent = czm_maximumComponent(lightColorHdr);
         vec3 clampedLightColor = lightColorHdr / max(maximumComponent, 1.0);
-        color += clampedLightColor* iblColor * material.occlusion;
+        color += clampedLightColor * iblColor * material.occlusion;
     #endif
 
     float clearcoatFactor = material.clearcoatFactor;