New option for detecting feature edges at material boundaries.

A checkbox "Material Boundaries" has been added to the Freestyle
options in the Layers tab of the Render buttons.  By enabling the
option, any edge between two faces with different materials is
detected as a feature edge.  In style modules, edges at material
boundaries can be tested with pyNatureUP1D(Nature.MATERIAL_BOUNDARY).

source/blender/freestyle/intern/python/BPy_Nature.cpp

@@ -174,6 +174,10 @@ static PyLongObject _Nature_SUGGESTIVE_CONTOUR = {
 	PyVarObject_HEAD_INIT(&Nature_Type, 1)
 	{ Nature::SUGGESTIVE_CONTOUR }
 };
+static PyLongObject _Nature_MATERIAL_BOUNDARY = {
+	PyVarObject_HEAD_INIT(&Nature_Type, 1)
+	{ Nature::MATERIAL_BOUNDARY }
+};
 
 #define BPy_Nature_POINT               ((PyObject *)&_Nature_POINT)
 #define BPy_Nature_S_VERTEX            ((PyObject *)&_Nature_S_VERTEX)
@@ -188,6 +192,7 @@ static PyLongObject _Nature_SUGGESTIVE_CONTOUR = {
 #define BPy_Nature_RIDGE               ((PyObject *)&_Nature_RIDGE)
 #define BPy_Nature_VALLEY              ((PyObject *)&_Nature_VALLEY)
 #define BPy_Nature_SUGGESTIVE_CONTOUR  ((PyObject *)&_Nature_SUGGESTIVE_CONTOUR)
+#define BPy_Nature_MATERIAL_BOUNDARY   ((PyObject *)&_Nature_MATERIAL_BOUNDARY)
 
 //-------------------MODULE INITIALIZATION--------------------------------
 int Nature_Init( PyObject *module )
@@ -216,6 +221,7 @@ int Nature_Init( PyObject *module )
 	PyDict_SetItemString( Nature_Type.tp_dict, "RIDGE", BPy_Nature_RIDGE );
 	PyDict_SetItemString( Nature_Type.tp_dict, "VALLEY", BPy_Nature_VALLEY );
 	PyDict_SetItemString( Nature_Type.tp_dict, "SUGGESTIVE_CONTOUR", BPy_Nature_SUGGESTIVE_CONTOUR );
+	PyDict_SetItemString( Nature_Type.tp_dict, "MATERIAL_BOUNDARY", BPy_Nature_MATERIAL_BOUNDARY );
 
 	return 0;
 }