Added advanced diffuse shading models.

The traditional Lambertian model can only realistically simulate the diffuse component of _smooth_ surfaces; this commit adds two alternative models that give more realistic results for non-smooth surfaces:

The _Lommel-Seeliger_ model mimics very porous or dusty surfaces. While it has no parameters in and of itself, it is frequently used in a weighted average with the Lambertian model. To activate the Lommel-Seeliger model in POV-Ray, use `diffuse FLOAT lommel_seeliger on` for the pure model, or `diffuse FLOAT lommel_seeliger FLOAT` for a blend with the Lambertian model. The default is `lommel_seeliger 0.0`, indicating a blend of 0% Lommel-Seeliger and 100% Lambertian.

The _Oren-Nayar_ model extends the Lambertian model to mimic rough (but not porous) surfaces. To activate it in POV-Ray, use `diffuse FLOAT oren_nayar FLOAT`, where the parameter specifies the desired roughness (the _sigma_ parameter in the Oren-Nayar equations). The default is `oren_nayar 0.0`, indicating a perfectly smooth surface, in which case the Oren-Nayar model simplifies to the Lambertian model.

_NOTE:_ The new diffuse shading models are still highly experimental, and changes in syntax and/or functionality are almost guaranteed; most notably, the interaction with the `diffuse albedo FLOAT` syntax and the finish-level `fresnel` keyword still needs to be reviewed and possibly modified. Also, the parameterization of the Oren-Nayar model may be changed to better match the `roughness` parameterization for specular highlights.

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.8514084"
+#define POV_RAY_PRERELEASE "alpha.8545805"
 
 #if (POV_RAY_IS_AUTOBUILD == 1) && ((POV_RAY_IS_OFFICIAL == 1) || (POV_RAY_IS_SEMI_OFFICIAL == 1))
 #ifdef POV_RAY_PRERELEASE

source/core/material/texture.cpp

@@ -1153,18 +1153,21 @@ FINISH *Create_Finish()
     New->Reflection_Max.Clear();
     New->Reflection_Min.Clear();
 
-    New->Reflection_Fresnel     = false;
-    New->Reflection_Falloff     = 1;    /* Added by MBP 8/27/98 */
-    New->Diffuse                = 0.6;
-    New->DiffuseBack            = 0.0;
-    New->Brilliance             = 1.0;
-    New->BrillianceOut          = 1.0;
-    New->BrillianceAdjust       = 1.0;
-    New->BrillianceAdjustRad    = 1.0;
-    New->Phong                  = 0.0;
-    New->Phong_Size             = 40.0;
-    New->Specular               = 0.0;
-    New->Roughness              = 1.0 / 0.05;
+    New->Reflection_Fresnel         = false;
+    New->Reflection_Falloff         = 1;    /* Added by MBP 8/27/98 */
+    New->Diffuse                    = 0.6;
+    New->DiffuseBack                = 0.0;
+    New->Brilliance                 = 1.0;
+    New->BrillianceOut              = 1.0;
+    New->BrillianceAdjust           = 1.0;
+    New->BrillianceAdjustRad        = 1.0;
+    New->LommelSeeligerWeight       = 0.0;
+    New->OrenNayarA                 = 1.0;
+    New->OrenNayarB                 = 0.0;
+    New->Phong                      = 0.0;
+    New->Phong_Size                 = 40.0;
+    New->Specular                   = 0.0;
+    New->Roughness                  = 1.0 / 0.05;
 
     New->Crand = 0.0;
 

source/core/material/texture.h

@@ -118,6 +118,32 @@ struct Texture_Struct : public Pattern_Struct
 struct Finish_Struct
 {
     SNGL Diffuse, DiffuseBack, Brilliance, BrillianceOut, BrillianceAdjust, BrillianceAdjustRad;
+
+    /// How much of the diffuse contribution should be computed using the Lommel-Seeliger model.
+    ///
+    /// By default, POV-Ray uses a Lambertian-based diffuse reflectivity model. While this model is useful for
+    /// comparatively smooth surfaces, rough surfaces are better simulated using other models, one of the simplest
+    /// being the Lommel-Seeliger model. In astronomy, a weighted average of the Lambertian and Lommel-Seeliger models
+    /// is frequently used.
+    SNGL LommelSeeligerWeight;
+
+    /// @name Oren-Nayar diffuse model parameters.
+    ///
+    /// By default, POV-Ray uses a Lambertian-based diffuse reflectivity model. While this model is useful for
+    /// comparatively smooth surfaces, rough surfaces are better simulated using other models, one of which is the
+    /// (simplified) Oren-Nayar model, being a superset of the Lambertian model and governed by the following
+    /// parameters.
+    ///
+    /// @{
+
+    /// Factor A of the simplified Oren-Nayar model, defaulting to 1.0 for the Lambertian model.
+    SNGL OrenNayarA;
+
+    /// Factor B of the simplified Oren-Nayar model, defaulting to 0.0 for the Lambertian model.
+    SNGL OrenNayarB;
+
+    /// @}
+
     SNGL Specular, Roughness;
     SNGL Phong, Phong_Size;
     SNGL Irid, Irid_Film_Thickness, Irid_Turb;
@@ -129,9 +155,16 @@ struct Finish_Struct
     SNGL Reflection_Falloff;  // Added by MBP 8/27/98
     bool Reflection_Fresnel;
     bool Fresnel;
-    SNGL Reflect_Metallic; // MBP
-    int Conserve_Energy;  // added by NK Dec 19 1999
-    bool UseSubsurface;   // whether to use subsurface light transport
+    SNGL Reflect_Metallic;  // MBP
+    int Conserve_Energy;    // added by NK Dec 19 1999
+    bool UseSubsurface;     // whether to use subsurface light transport
+
+    void SetOrenNayarSigma(double sigma)
+    {
+        double sigmaSqr = sigma*sigma;
+        OrenNayarA = 1.0 - 0.50 * sigmaSqr / (sigmaSqr + 0.57);
+        OrenNayarB =       0.45 * sigmaSqr / (sigmaSqr + 0.09);
+    }
 };
 
 

source/core/render/trace.cpp

@@ -2373,19 +2373,37 @@ void Trace::ComputeShadowColour(const LightSource &lightsource, Intersection& is
 void Trace::ComputeDiffuseColour(const FINISH *finish, const Vector3d& lightDirection, const Vector3d& eyeDirection, const Vector3d& layer_normal, MathColour& colour, const MathColour& light_colour,
                                  const MathColour& layer_pigment_colour, double relativeIor, double attenuation, bool backside)
 {
-    double cos_angle_of_incidence, intensity;
+    double cos_in, cos_out, intensity;
     double diffuse = (backside? finish->DiffuseBack : finish->Diffuse) * finish->BrillianceAdjust;
 
     if (diffuse <= 0.0)
         return;
 
-    cos_angle_of_incidence = dot(layer_normal, lightDirection);
+    cos_in = dot(layer_normal, lightDirection);
 
     // Brilliance is likely to be 1.0 (default value)
     if(finish->Brilliance != 1.0)
-        intensity = pow(fabs(cos_angle_of_incidence), (double) finish->Brilliance);
+        intensity = pow(fabs(cos_in), (double) finish->Brilliance);
     else
-        intensity = fabs(cos_angle_of_incidence);
+        intensity = fabs(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));
+
+    if (finish->OrenNayarB != 0.0)
+    {
+        Vector3d projected_in  = lightDirection - layer_normal * cos_in;
+        Vector3d projected_out = -eyeDirection  - layer_normal * cos_out;
+        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 *= diffuse * attenuation;
 
@@ -2395,9 +2413,8 @@ void Trace::ComputeDiffuseColour(const FINISH *finish, const Vector3d& lightDire
     if (finish->Fresnel)
     {
         MathColour cs1, cs2;
-        ComputeFresnel(cs1, MathColour(0.0), MathColour(1.0), cos_angle_of_incidence, relativeIor);
-        cos_angle_of_incidence = -dot(layer_normal, eyeDirection);
-        ComputeFresnel(cs2, MathColour(0.0), MathColour(1.0), cos_angle_of_incidence, relativeIor);
+        ComputeFresnel(cs1, MathColour(0.0), MathColour(1.0), cos_in,  relativeIor);
+        ComputeFresnel(cs2, MathColour(0.0), MathColour(1.0), cos_out, relativeIor);
         colour += intensity * layer_pigment_colour * light_colour * cs1 * cs2;
     }
     else

source/parser/parser.h

@@ -156,7 +156,9 @@ struct ExperimentalFlags
 {
     bool    backsideIllumination    : 1;
     bool    functionHf              : 1;
+    bool    lommelSeeliger          : 1;
     bool    meshCamera              : 1;
+    bool    orenNayar               : 1;
     bool    slopeAltitude           : 1;
     bool    spline                  : 1;
     bool    subsurface              : 1;
@@ -166,7 +168,9 @@ struct ExperimentalFlags
     ExperimentalFlags() :
         backsideIllumination(false),
         functionHf(false),
+        lommelSeeliger(false),
         meshCamera(false),
+        orenNayar(false),
         slopeAltitude(false),
         spline(false),
         subsurface(false),

source/parser/parser_materials.cpp

@@ -2371,6 +2371,18 @@ void Parser::Parse_Finish (FINISH **Finish_Ptr)
                 mExperimentalFlags.backsideIllumination = true;
         END_CASE
 
+        CASE (LOMMEL_SEELIGER_TOKEN)
+            New->LommelSeeligerWeight = Parse_Float ();
+            mExperimentalFlags.lommelSeeliger = true;
+        END_CASE
+
+        CASE (OREN_NAYAR_TOKEN)
+            New->SetOrenNayarSigma(Parse_Float ());
+            mExperimentalFlags.orenNayar = true;
+            PossibleError("Parameterization of the Oren-Nayar diffuse model has not been finalized yet."
+                          " Expect future versions of POV-Ray to render this scene differently without warning.");
+        END_CASE
+
         CASE (REFLECTION_TOKEN)
         {
             bool found_second_color = false;
@@ -2598,6 +2610,30 @@ void Parser::Parse_Finish (FINISH **Finish_Ptr)
     END_EXPECT    /* End of finish_mods */
 #endif
 
+    if ((New->OrenNayarA != 1.0) || (New->OrenNayarB != 0.0))
+    {
+        if (New->Fresnel)
+            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)
+    {
+        if (New->Fresnel)
+            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)
     {
         // As of version 3.7, use of "ambient" to model glowing materials is deprecated, and "emission" should be used

source/parser/reservedwords.cpp

@@ -320,6 +320,7 @@ const RESERVED_WORD Reserved_Words[LAST_TOKEN] = {
     {LOCAL_TOKEN, "local"},
     {LOCATION_TOKEN, "location"},
     {LOG_TOKEN, "log"},
+    {LOMMEL_SEELIGER_TOKEN, "lommel_seeliger"},
     {LOOKS_LIKE_TOKEN, "looks_like"},
     {LOOK_AT_TOKEN, "look_at"},
     {LOW_ERROR_FACTOR_TOKEN, "low_error_factor" },
@@ -389,6 +390,7 @@ const RESERVED_WORD Reserved_Words[LAST_TOKEN] = {
     {ON_TOKEN, "on"},
     {OPEN_TOKEN, "open"},
     {OPTIONAL_TOKEN, "optional"},
+    {OREN_NAYAR_TOKEN, "oren_nayar"},
     {ORIENTATION_TOKEN, "orientation"},
     {ORIENT_TOKEN,"orient"},
     {ORTHOGRAPHIC_TOKEN, "orthographic"},

source/parser/reservedwords.h

@@ -249,6 +249,7 @@ enum TOKEN_IDS
     LEOPARD_TOKEN,
     LIGHT_SOURCE_TOKEN,
     LOCATION_TOKEN,
+    LOMMEL_SEELIGER_TOKEN,
     LOOKS_LIKE_TOKEN,
     LOOK_AT_TOKEN,
     MANDEL_TOKEN,
@@ -269,6 +270,7 @@ enum TOKEN_IDS
     ONCE_TOKEN,
     ONION_TOKEN,
     OPTIONAL_TOKEN,
+    OREN_NAYAR_TOKEN,
     OVUS_TOKEN,
     PERCENT_TOKEN,
     PHASE_TOKEN,

unix/VERSION

@@ -1 +1 @@
-3.7.1-alpha.8514084
+3.7.1-alpha.8545805