Composite Filament planar reflections as Fresnel-weighted specular.

PiperOrigin-RevId: 960554436
Change-Id: Ife6f5c760993ad185e9421cd7b3ce7fd06fffc90

src/render/filament/assets/phong_2d_reflect.mat

@@ -15,6 +15,7 @@
 material {
     name : phong_2d_reflect,
     shadingModel : specularGlossiness,
+    postLightingBlending : add,
     flipUV : false,
     parameters : [
         { type : float4, name : BaseColorFactor },
@@ -51,8 +52,12 @@ fragment {
     material.emissive      = vec4(
         materialParams.BaseColorFactor.rgb * materialParams.EmissiveFactor, 0.0);
 
-    // Apply reflection.
+    // The reflection is radiance arriving from the mirror direction, so it is
+    // weighted by the Fresnel term and added after lighting. Reflectance is
+    // the reflectivity at normal incidence; grazing angles approach a mirror.
     vec4 reflection = texture(materialParams_Reflection, screen_uv);
-    material.baseColor.rgb = mix(material.baseColor.rgb, reflection.rgb, materialParams.Reflectance);
+    float f0 = materialParams.Reflectance;
+    float fresnel = f0 + (1.0 - f0) * pow(1.0 - getNdotV(), 5.0);
+    material.postLightingColor = vec4(reflection.rgb * fresnel, 0.0);
   }
 }

src/render/filament/assets/phong_2d_uv_reflect.mat

@@ -15,6 +15,7 @@
 material {
     name : phong_2d_uv_reflect,
     shadingModel : specularGlossiness,
+    postLightingBlending : add,
     flipUV : false,
     parameters : [
         { type : float4, name : BaseColorFactor },
@@ -43,8 +44,12 @@ fragment {
     material.emissive      = vec4(
         materialParams.BaseColorFactor.rgb * materialParams.EmissiveFactor, 0.0);
 
-    // Apply reflection.
+    // The reflection is radiance arriving from the mirror direction, so it is
+    // weighted by the Fresnel term and added after lighting. Reflectance is
+    // the reflectivity at normal incidence; grazing angles approach a mirror.
     vec4 reflection = texture(materialParams_Reflection, screen_uv);
-    material.baseColor.rgb = mix(material.baseColor.rgb, reflection.rgb, materialParams.Reflectance);
+    float f0 = materialParams.Reflectance;
+    float fresnel = f0 + (1.0 - f0) * pow(1.0 - getNdotV(), 5.0);
+    material.postLightingColor = vec4(reflection.rgb * fresnel, 0.0);
   }
 }

src/render/filament/assets/phong_color_reflect.mat

@@ -15,6 +15,7 @@
 material {
     name : phong_color_reflect,
     shadingModel : specularGlossiness,
+    postLightingBlending : add,
     parameters : [
         { type : float4, name : BaseColorFactor },
         { type : float, name : SpecularFactor },
@@ -36,8 +37,12 @@ fragment {
     material.emissive      = vec4(
         materialParams.BaseColorFactor.rgb * materialParams.EmissiveFactor, 0.0);
 
-    // Apply reflection.
+    // The reflection is radiance arriving from the mirror direction, so it is
+    // weighted by the Fresnel term and added after lighting. Reflectance is
+    // the reflectivity at normal incidence; grazing angles approach a mirror.
     vec4 reflection = texture(materialParams_Reflection, screen_uv);
-    material.baseColor.rgb = mix(material.baseColor.rgb, reflection.rgb, materialParams.Reflectance);
+    float f0 = materialParams.Reflectance;
+    float fresnel = f0 + (1.0 - f0) * pow(1.0 - getNdotV(), 5.0);
+    material.postLightingColor = vec4(reflection.rgb * fresnel, 0.0);
   }
 }

src/render/filament/assets/phong_cube_reflect.mat

@@ -15,6 +15,7 @@
 material {
     name : phong_cube_reflect,
     shadingModel : specularGlossiness,
+    postLightingBlending : add,
     flipUV : false,
     parameters : [
         { type : float4, name : BaseColorFactor },
@@ -50,8 +51,12 @@ fragment {
     material.emissive      = vec4(
         materialParams.BaseColorFactor.rgb * materialParams.EmissiveFactor, 0.0);
 
-    // Apply reflection.
+    // The reflection is radiance arriving from the mirror direction, so it is
+    // weighted by the Fresnel term and added after lighting. Reflectance is
+    // the reflectivity at normal incidence; grazing angles approach a mirror.
     vec4 reflection = texture(materialParams_Reflection, screen_uv);
-    material.baseColor.rgb = mix(material.baseColor.rgb, reflection.rgb, materialParams.Reflectance);
+    float f0 = materialParams.Reflectance;
+    float fresnel = f0 + (1.0 - f0) * pow(1.0 - getNdotV(), 5.0);
+    material.postLightingColor = vec4(reflection.rgb * fresnel, 0.0);
   }
 }