gltfio: fix occlusion strength

Fixes #6106

RELEASE_NOTES.md

@@ -8,6 +8,7 @@ A new header is inserted each time a *tag* is created.
 - engine: LiSPSM is now a user settable option
 - Java: Fix TransformManager.getChildren()
 - Metal: newer devices are no longer limited to 16 samplers per Material.
+- gltfio: fix interpretation of occlusion strength
 
 ## v1.27.2
 

libs/gltfio/materials/base.mat.in

@@ -163,8 +163,8 @@ fragment {
             if (materialParams.aoIndex > -1) {
                 highp float2 uv = uvs[materialParams.aoIndex];
                 uv = (vec3(uv, 1.0) * materialParams.occlusionUvMatrix).xy;
-                material.ambientOcclusion = texture(materialParams_occlusionMap, uv).r *
-                        materialParams.aoStrength;
+                float occlusion = texture(materialParams_occlusionMap, uv).r;
+                material.ambientOcclusion = 1.0 + materialParams.aoStrength * (occlusion - 1.0);
             }
             if (materialParams.emissiveIndex > -1) {
                 highp float2 uv = uvs[materialParams.emissiveIndex];

libs/gltfio/materials/sheen.mat.in

@@ -127,8 +127,8 @@ fragment {
         if (materialParams.aoIndex > -1) {
             highp float2 uv = uvs[materialParams.aoIndex];
             uv = (vec3(uv, 1.0) * materialParams.occlusionUvMatrix).xy;
-            material.ambientOcclusion = texture(materialParams_occlusionMap, uv).r *
-                    materialParams.aoStrength;
+            float occlusion = texture(materialParams_occlusionMap, uv).r;
+            material.ambientOcclusion = 1.0 + materialParams.aoStrength * (occlusion - 1.0);
         }
         if (materialParams.emissiveIndex > -1) {
             highp float2 uv = uvs[materialParams.emissiveIndex];

libs/gltfio/materials/transmission.mat.in

@@ -117,8 +117,8 @@ fragment {
         if (materialParams.aoIndex > -1) {
             highp float2 uv = uvs[materialParams.aoIndex];
             uv = (vec3(uv, 1.0) * materialParams.occlusionUvMatrix).xy;
-            material.ambientOcclusion = texture(materialParams_occlusionMap, uv).r *
-                    materialParams.aoStrength;
+            float occlusion = texture(materialParams_occlusionMap, uv).r;
+            material.ambientOcclusion = 1.0 + materialParams.aoStrength * (occlusion - 1.0);
         }
         if (materialParams.emissiveIndex > -1) {
             highp float2 uv = uvs[materialParams.emissiveIndex];

libs/gltfio/materials/volume.mat.in

@@ -133,8 +133,8 @@ fragment {
         if (materialParams.aoIndex > -1) {
             highp float2 uv = uvs[materialParams.aoIndex];
             uv = (vec3(uv, 1.0) * materialParams.occlusionUvMatrix).xy;
-            material.ambientOcclusion = texture(materialParams_occlusionMap, uv).r *
-                    materialParams.aoStrength;
+            float occlusion = texture(materialParams_occlusionMap, uv).r;
+            material.ambientOcclusion = 1.0 + materialParams.aoStrength * (occlusion - 1.0);
         }
         if (materialParams.emissiveIndex > -1) {
             highp float2 uv = uvs[materialParams.emissiveIndex];

libs/gltfio/src/JitShaderProvider.cpp

@@ -194,8 +194,8 @@ std::string shaderFromKey(const MaterialKey& config) {
                 shader += "aoUV = (vec3(aoUV, 1.0) * materialParams.occlusionUvMatrix).xy;\n";
             }
             shader += R"SHADER(
-                material.ambientOcclusion = texture(materialParams_occlusionMap, aoUV).r *
-                        materialParams.aoStrength;
+                float occlusion = texture(materialParams_occlusionMap, aoUV).r;
+                material.ambientOcclusion = 1.0 + materialParams.aoStrength * (occlusion - 1.0);
             )SHADER";
         }
         if (config.hasEmissiveTexture) {