Add new shading model to Filament for specularGlossiness.

android/filamat-android/src/main/java/com/google/android/filament/filamat/MaterialBuilder.java

@@ -34,7 +34,8 @@ public enum Shading {
         UNLIT,                  // no lighting applied, emissive possible
         LIT,                    // default, standard lighting
         SUBSURFACE,             // subsurface lighting model
-        CLOTH                   // cloth lighting model
+        CLOTH,                  // cloth lighting model
+        SPECULAR_GLOSSINESS     // legacy lighting model
     }
 
     public enum Interpolation {

android/filament-android/src/main/java/com/google/android/filament/Material.java

@@ -37,7 +37,8 @@ public enum Shading {
         UNLIT,
         LIT,
         SUBSURFACE,
-        CLOTH
+        CLOTH,
+        SPECULAR_GLOSSINESS
     }
 
     public enum Interpolation {

docs/Materials.md.html

@@ -59,6 +59,7 @@
 - Subsurface
 - Cloth
 - Unlit
+- Specular glossiness (legacy)
 
 ## Lit model
 
@@ -522,6 +523,36 @@
 
 ![Figure [materialUnlit]: The unlit model is used to render debug information](images/screenshot_unlit.jpg)
 
+## Specular glossiness
+
+This alternative lighting model exists to comply with legacy standards.
+
+Similar to cloth, it encompasses all the parameters previously defined for the standard
+lit mode except for _metallic_ and _reflectance_, and adds a _sheenColor_ parameter. The sheen
+color is used to formulate the BRDF inputs as follows.
+
+```glsl
+pixel.diffuseColor = baseColor * (1.0 - max(sheen.r, sheen.g, sheen.b));
+pixel.f0 = sheen;
+```
+
+This is not a physically-based formulation, so we do not recommend using the `specularGlossiness`
+model except when loading legacy assets.
+
+Parameter      |      Definition
+---------------------:|:---------------------
+**baseColor**         | Surface diffuse color
+**sheenColor**        | Specular tint (defaults to $\sqrt{baseColor}$)
+[Table [glossinessProperties]: Properties of the specular-glossiness shading model]
+
+The type and range of each property is described in table [glossinessPropertiesTypes].
+
+       Property       |   Type   |            Range         |           Note
+---------------------:|:--------:|:------------------------:|:-------------------------
+**baseColor**         | float4   |  [0..1]                  | Pre-multiplied linear RGB
+**sheenColor**        | float3   |  [0..1]                  | Linear RGB
+[Table [glossinessPropertiesTypes]: Range and type of the specular-glossiness model's properties]
+
 # Material definitions
 
 A material definition is a text file that describes all the information required by a material:
@@ -656,7 +687,7 @@
 :    `string`
 
 Value
-:     Any of `lit`, `subsurface`, `cloth`, `unlit`. Defaults to `lit`.
+:     Any of `lit`, `subsurface`, `cloth`, `unlit`, `specularGlossiness`. Defaults to `lit`.
 
 Description
 :     Selects the material model as described in the Material models section.
@@ -1387,8 +1418,8 @@
 
     // no other field is available with the unlit shading model
     float  roughness;           // default: 1.0
-    float  metallic;            // default: 0.0, not available with cloth
-    float  reflectance;         // default: 0.5, not available with cloth
+    float  metallic;            // default: 0.0, not available with cloth or specularGlossiness
+    float  reflectance;         // default: 0.5, not available with cloth or specularGlossiness
     float  ambientOcclusion;    // default: 0.0
 
     // not available when the shading model is subsurface or cloth
@@ -1407,6 +1438,9 @@
     float3 sheenColor;          // default: sqrt(baseColor)
     float3 subsurfaceColor;     // default: float3(0.0)
 
+    // only available when the shading model is specularGlossiness
+    float3 sheenColor;          // default: sqrt(baseColor)
+
     // not available when the shading model is unlit
     // must be set before calling prepareMaterial()
     float3 normal;              // default: float3(0.0, 0.0, 1.0)

libs/filabridge/include/filament/MaterialEnums.h

@@ -36,6 +36,7 @@ enum class Shading : uint8_t {
     LIT,                    //!< default, standard lighting
     SUBSURFACE,             //!< subsurface lighting model
     CLOTH,                  //!< cloth lighting model
+    SPECULAR_GLOSSINESS,    //!< legacy lighting model
 };
 
 /**

libs/filamat/include/filamat/MaterialBuilder.h

@@ -126,7 +126,7 @@ class UTILS_PUBLIC MaterialBuilder : public MaterialBuilderBase {
         THICKNESS,               // float,  subsurface shading model only
         SUBSURFACE_POWER,        // float,  subsurface shading model only
         SUBSURFACE_COLOR,        // float3, subsurface and cloth shading models only
-        SHEEN_COLOR,             // float3, cloth shading model only
+        SHEEN_COLOR,             // float3, cloth and specular-glossiness shading models only
         EMISSIVE,                // float4, all shading models
         NORMAL,                  // float3, all shading models only, except unlit
         POST_LIGHTING_COLOR,     // float4, all shading models

libs/filamat/src/shaders/CodeGenerator.cpp

@@ -450,6 +450,7 @@ std::ostream& CodeGenerator::generateShaderLit(std::ostream& out, ShaderType typ
             case Shading::UNLIT:
                 assert("Lit shader generated with unlit shading model");
                 break;
+            case Shading::SPECULAR_GLOSSINESS:
             case Shading::LIT:
                 out << SHADERS_SHADING_MODEL_STANDARD_FS_DATA;
                 break;

libs/filamat/src/shaders/ShaderGenerator.cpp

@@ -38,10 +38,11 @@ namespace filamat {
 
 static const char* getShadingDefine(filament::Shading shading) noexcept {
     switch (shading) {
-        case filament::Shading::LIT:         return "SHADING_MODEL_LIT";
-        case filament::Shading::UNLIT:       return "SHADING_MODEL_UNLIT";
-        case filament::Shading::SUBSURFACE:  return "SHADING_MODEL_SUBSURFACE";
-        case filament::Shading::CLOTH:       return "SHADING_MODEL_CLOTH";
+        case filament::Shading::LIT:                 return "SHADING_MODEL_LIT";
+        case filament::Shading::UNLIT:               return "SHADING_MODEL_UNLIT";
+        case filament::Shading::SUBSURFACE:          return "SHADING_MODEL_SUBSURFACE";
+        case filament::Shading::CLOTH:               return "SHADING_MODEL_CLOTH";
+        case filament::Shading::SPECULAR_GLOSSINESS: return "SHADING_MODEL_SPECULAR_GLOSSINESS";
     }
 }
 

shaders/src/common_lighting.fs

@@ -46,7 +46,7 @@ struct PixelParams {
     float subsurfacePower;
 #endif
 
-#if defined(SHADING_MODEL_CLOTH) && defined(MATERIAL_HAS_SUBSURFACE_COLOR)
+#if (defined(SHADING_MODEL_CLOTH) || defined(SHADING_MODEL_SPECULAR_GLOSSINESS)) && defined(MATERIAL_HAS_SUBSURFACE_COLOR)
     vec3  subsurfaceColor;
 #endif
 };

shaders/src/common_material.fs

@@ -61,7 +61,7 @@ struct MaterialInputs {
     vec4  baseColor;
 #if !defined(SHADING_MODEL_UNLIT)
     float roughness;
-#if !defined(SHADING_MODEL_CLOTH)
+#if !defined(SHADING_MODEL_CLOTH) && !defined(SHADING_MODEL_SPECULAR_GLOSSINESS)
     float metallic;
     float reflectance;
 #endif
@@ -81,7 +81,7 @@ struct MaterialInputs {
     vec3  subsurfaceColor;
 #endif
 
-#if defined(SHADING_MODEL_CLOTH)
+#if defined(SHADING_MODEL_CLOTH) || defined(SHADING_MODEL_SPECULAR_GLOSSINESS)
     vec3  sheenColor;
 #if defined(MATERIAL_HAS_SUBSURFACE_COLOR)
     vec3  subsurfaceColor;
@@ -104,7 +104,7 @@ void initMaterial(out MaterialInputs material) {
     material.baseColor = vec4(1.0);
 #if !defined(SHADING_MODEL_UNLIT)
     material.roughness = 1.0;
-#if !defined(SHADING_MODEL_CLOTH)
+#if !defined(SHADING_MODEL_CLOTH) && !defined(SHADING_MODEL_SPECULAR_GLOSSINESS)
     material.metallic = 0.0;
     material.reflectance = 0.5;
 #endif
@@ -128,7 +128,7 @@ void initMaterial(out MaterialInputs material) {
     material.subsurfaceColor = vec3(1.0);
 #endif
 
-#if defined(SHADING_MODEL_CLOTH)
+#if defined(SHADING_MODEL_CLOTH) || defined(SHADING_MODEL_SPECULAR_GLOSSINESS)
     material.sheenColor = sqrt(material.baseColor.rgb);
 #if defined(MATERIAL_HAS_SUBSURFACE_COLOR)
     material.subsurfaceColor = vec3(0.0);

shaders/src/shading_lit.fs

@@ -27,7 +27,13 @@ void getPixelParams(const MaterialInputs material, out PixelParams pixel) {
     baseColor.rgb /= max(baseColor.a, FLT_EPS);
 #endif
 
-#if !defined(SHADING_MODEL_CLOTH)
+#if defined(SHADING_MODEL_SPECULAR_GLOSSINESS)
+    // This is from KHR_materials_pbrSpecularGlossiness.
+    vec3 specular = material.sheenColor;
+    float maxSpecularComponent = max(max(specular.r, specular.g), specular.b);
+    pixel.diffuseColor = baseColor.rgb * (1.0 - maxSpecularComponent);
+    pixel.f0 = specular;
+#elif !defined(SHADING_MODEL_CLOTH)
     float metallic = material.metallic;
     float reflectance = material.reflectance;
 

tools/matc/src/matc/ParametersProcessor.cpp

@@ -136,6 +136,7 @@ ParametersProcessor::ParametersProcessor() {
     mStringToShading["lit"] = MaterialBuilder::Shading::LIT;
     mStringToShading["subsurface"] = MaterialBuilder::Shading::SUBSURFACE;
     mStringToShading["unlit"] = MaterialBuilder::Shading::UNLIT;
+    mStringToShading["specularGlossiness"] = MaterialBuilder::Shading::SPECULAR_GLOSSINESS;
 
     mStringToVariant["directionalLighting"] = filament::Variant::DIRECTIONAL_LIGHTING;
     mStringToVariant["dynamicLighting"] = filament::Variant::DYNAMIC_LIGHTING;

tools/matinfo/src/main.cpp

@@ -243,6 +243,7 @@ const char* toString(Shading shadingModel) {
         case Shading::LIT: return "lit";
         case Shading::SUBSURFACE: return "subsurface";
         case Shading::CLOTH: return "cloth";
+        case Shading::SPECULAR_GLOSSINESS: return "specularGlossiness";
     }
 }