Improvements to advanced diffuse shading models.

- Fixed a bug in the Oren-Nayar implementation.
- Changed the interaction between the Oren-Nayar and Lommel-Seeliger models to work as originally intended, with `lommel_seeliger K oren_nayar SIGMA` giving a  K:(1-K) weighted average of Lommel-Seeliger and Oren-Nayar).
- Implemented mechanisms to compensate for the reduced effective brightness of the Oren-Nayar and Lommel-Seeliger models when using canonical brightness parameterization. Using `diffuse albedo FLOAT` should now give identical bihemispherical albedos (ratio of total outgoing light vs. total incoming light) for all models. Also, when using canonical brightness parameterization (`diffuse FLOAT`), the Lambertian-based approximation used in radiosity should now match the effective bihemispherical albedo.

Author: c-lipka

source/base/version.h

@@ -45,7 +45,7 @@
 #define OFFICIAL_VERSION_STRING "3.7.1"
 #define OFFICIAL_VERSION_NUMBER 371
 
-#define POV_RAY_PRERELEASE "alpha.8545805"
+#define POV_RAY_PRERELEASE "alpha.8555867"
 
 #if (POV_RAY_IS_AUTOBUILD == 1) && ((POV_RAY_IS_OFFICIAL == 1) || (POV_RAY_IS_SEMI_OFFICIAL == 1))
 #ifdef POV_RAY_PRERELEASE

source/core/lighting/photons.cpp

@@ -460,7 +460,7 @@ void PhotonTrace::ComputeLightedTexture(MathColour& LightCol, ColourChannel&, co
         diffuseWeight = ResCol.WeightAbsGreyscale();
         // use top-layer finish only
         if(Texture->Finish)
-            diffuseWeight*=Texture->Finish->Diffuse * Texture->Finish->BrillianceAdjust;
+            diffuseWeight*=Texture->Finish->Diffuse * Texture->Finish->DiffuseAlbedoAdjust;
         refractionWeight = Trans;
         // reflection only for top layer!!!!!!
         // TODO is "rend()" the top layer or the bottom layer???

source/core/material/texture.cpp

@@ -1159,8 +1159,8 @@ FINISH *Create_Finish()
     New->DiffuseBack                = 0.0;
     New->Brilliance                 = 1.0;
     New->BrillianceOut              = 1.0;
-    New->BrillianceAdjust           = 1.0;
-    New->BrillianceAdjustRad        = 1.0;
+    New->DiffuseAlbedoAdjust        = 1.0;
+    New->DiffuseAlbedoAdjustRad     = 1.0;
     New->LommelSeeligerWeight       = 0.0;
     New->OrenNayarA                 = 1.0;
     New->OrenNayarB                 = 0.0;

source/core/material/texture.h

@@ -117,7 +117,7 @@ struct Texture_Struct : public Pattern_Struct
 
 struct Finish_Struct
 {
-    SNGL Diffuse, DiffuseBack, Brilliance, BrillianceOut, BrillianceAdjust, BrillianceAdjustRad;
+    SNGL Diffuse, DiffuseBack, Brilliance, BrillianceOut, DiffuseAlbedoAdjust, DiffuseAlbedoAdjustRad;
 
     /// How much of the diffuse contribution should be computed using the Lommel-Seeliger model.
     ///

source/core/render/trace.cpp

@@ -882,7 +882,7 @@ void Trace::ComputeLightedTexture(MathColour& resultColour, ColourChannel& resul
 
                 if (sceneData->radiositySettings.brilliance)
                 {
-                    diffuse    *= layer->Finish->BrillianceAdjustRad;
+                    diffuse    *= layer->Finish->DiffuseAlbedoAdjustRad;
                     brilliance =  layer->Finish->Brilliance;
                 }
 
@@ -909,7 +909,7 @@ void Trace::ComputeLightedTexture(MathColour& resultColour, ColourChannel& resul
 
                 diffuse = layer->Finish->DiffuseBack;
                 if (sceneData->radiositySettings.brilliance)
-                    diffuse *= layer->Finish->BrillianceAdjustRad;
+                    diffuse *= layer->Finish->DiffuseAlbedoAdjustRad;
 
                 // if backside radiosity calculation needed, but not yet done, do it now
                 // TODO FIXME - [CLi] with "normal on", shouldn't we compute radiosity for each layer separately (if it has pertubed normals)?
@@ -2374,35 +2374,40 @@ void Trace::ComputeDiffuseColour(const FINISH *finish, const Vector3d& lightDire
                                  const MathColour& layer_pigment_colour, double relativeIor, double attenuation, bool backside)
 {
     double cos_in, cos_out, intensity;
-    double diffuse = (backside? finish->DiffuseBack : finish->Diffuse) * finish->BrillianceAdjust;
+    double diffuse = (backside? finish->DiffuseBack : finish->Diffuse) * finish->DiffuseAlbedoAdjust;
 
     if (diffuse <= 0.0)
         return;
 
-    cos_in = dot(layer_normal, lightDirection);
+    cos_in = fabs(dot(layer_normal, lightDirection));
 
     // Brilliance is likely to be 1.0 (default value)
     if(finish->Brilliance != 1.0)
-        intensity = pow(fabs(cos_in), (double) finish->Brilliance);
+        intensity = pow(cos_in, (double) finish->Brilliance);
     else
-        intensity = fabs(cos_in);
+        intensity = cos_in;
 
     if (finish->Fresnel || (finish->LommelSeeligerWeight != 0.0) || (finish->OrenNayarB != 0.0))
-        cos_out = -dot(layer_normal, eyeDirection);
-
-    if (finish->LommelSeeligerWeight != 0.0)
-        intensity *= (1.0 - finish->LommelSeeligerWeight + finish->LommelSeeligerWeight / (cos_in + cos_out));
+        cos_out = fabs(dot(layer_normal, eyeDirection));
 
+    if (finish->OrenNayarA != 1.0)
+        intensity *= finish->OrenNayarA;
     if (finish->OrenNayarB != 0.0)
     {
-        Vector3d projected_in  = lightDirection - layer_normal * cos_in;
-        Vector3d projected_out = -eyeDirection  - layer_normal * cos_out;
+        Vector3d projected_in  = (lightDirection - layer_normal * cos_in ).normalized();
+        Vector3d projected_out = (-eyeDirection  - layer_normal * cos_out).normalized();
         double cos_phi = dot(projected_in, projected_out);
         double theta_in  = acos(cos_in);
         double theta_out = acos(cos_out);
         double alpha = max(theta_in, theta_out);
         double beta  = min(theta_in, theta_out);
-        intensity *= (finish->OrenNayarA + finish->OrenNayarB*max(0.0,cos_phi)*sin(alpha)*tan(beta));
+        intensity += finish->OrenNayarB * cos_in * max(0.0,cos_phi) * sin(alpha) * tan(beta);
+    }
+
+    if (finish->LommelSeeligerWeight != 0.0)
+    {
+        intensity *= (1.0 - finish->LommelSeeligerWeight);
+        intensity += finish->LommelSeeligerWeight * cos_in / (cos_in + cos_out);
     }
 
     intensity *= diffuse * attenuation;

source/parser/parser_materials.cpp

@@ -2616,10 +2616,6 @@ void Parser::Parse_Finish (FINISH **Finish_Ptr)
             PossibleError("Finish-level 'fresnel' keyword found in combination with the Oren-Nayar diffuse model."
                           " The interaction of these features has not been finalized yet, and is known to be bogus."
                           " Expect future versions of POV-Ray to render this scene differently without warning.");
-        if (diffuseAdjust)
-            PossibleError("'diffuse albedo' found in combination with the Oren-Nayar diffuse model."
-                          " The interaction of these features has not been finalized yet."
-                          " Expect future versions of POV-Ray to render this scene differently without warning.");
     }
 
     if (New->LommelSeeligerWeight != 0.0)
@@ -2628,10 +2624,6 @@ void Parser::Parse_Finish (FINISH **Finish_Ptr)
             PossibleError("Finish-level 'fresnel' keyword found in combination with the Lommel-Seeliger diffuse model."
                           " The interaction of these features has not been finalized yet, and is known to be bogus."
                           " Expect future versions of POV-Ray to render this scene differently without warning.");
-        if (diffuseAdjust)
-            PossibleError("'diffuse albedo' found in combination with the Lommel_Seeliger diffuse model."
-                          " The interaction of these features has not been finalized yet."
-                          " Expect future versions of POV-Ray to render this scene differently without warning.");
     }
 
     if ((sceneData->EffectiveLanguageVersion() >= 370) && ambientSet)
@@ -2659,15 +2651,25 @@ void Parser::Parse_Finish (FINISH **Finish_Ptr)
     // adjust diffuse, phong and/or specular intensity parameters
     // so that a user-specified value of 1.0 corresponds to a
     // backscattering of 100% of the incoming light
+    double EffectiveBiHemisphericalAlbedo = 2.0 / (New->Brilliance + 1.0);
+    if (New->OrenNayarA != 1.0)
+        EffectiveBiHemisphericalAlbedo *= New->OrenNayarA;
+    if (New->OrenNayarB != 0.0)
+        EffectiveBiHemisphericalAlbedo += New->OrenNayarB * (2.0/3.0 - (64.0/45.0)*(1.0/M_PI));
+    if (New->LommelSeeligerWeight != 0.0)
+    {
+        EffectiveBiHemisphericalAlbedo *= (1.0 - New->LommelSeeligerWeight);
+        EffectiveBiHemisphericalAlbedo += New->LommelSeeligerWeight * ((8.0 * (1.0-log(2.0))) / 3.0);
+    }
     if (diffuseAdjust)
     {
-        New->BrillianceAdjust    = (New->Brilliance + 1.0) / 2.0;
-        New->BrillianceAdjustRad = 1.0;
+        New->DiffuseAlbedoAdjust    = 1.0 / EffectiveBiHemisphericalAlbedo;
+        New->DiffuseAlbedoAdjustRad = 1.0;
     }
     else
     {
-        New->BrillianceAdjust    = 1.0;
-        New->BrillianceAdjustRad = 2.0 / (New->Brilliance + 1.0);
+        New->DiffuseAlbedoAdjust    = 1.0;
+        New->DiffuseAlbedoAdjustRad = EffectiveBiHemisphericalAlbedo;
     }
     if (phongAdjust)
         New->Phong *= (New->Phong_Size + 1.0) / 2.0;

unix/VERSION

@@ -1 +1 @@
-3.7.1-alpha.8545805
+3.7.1-alpha.8555867