Fix T43624: Freestyle uses wrong colour on second Line Set with textured lines in Cycles.

This is a regression introduced by rBd8b00a3bf5c1 (Freestyle: memory
consumption optimization in stroke rendering).

The issue was caused by uninitialized MPoly::mat_nr values.  Before the
stroke rendering optimization, individual Freestyle strokes were
represented by distinct mesh objects, and thus MPoly::mat_nr was left
unset (i.e., was always zero).  Now that the stroke rendering optimization
has been done and mesh objects may represent multiple strokes of different
materials, MPoly::mat_nr had to be properly set to the material index that
refers to the material of the poly face.

1 files changed, 2 insertions, 1 deletions

diff --git a/source/blender/freestyle/intern/blender_interface/BlenderStrokeRenderer.cpp b/source/blender/freestyle/intern/blender_interface/BlenderStrokeRenderer.cpp
index 70de246a8de..f304e8ae9bd 100644
--- a/source/blender/freestyle/intern/blender_interface/BlenderStrokeRenderer.cpp
+++ b/source/blender/freestyle/intern/blender_interface/BlenderStrokeRenderer.cpp
@@ -730,7 +730,6 @@ void BlenderStrokeRenderer::GenerateStrokeMesh(StrokeGroup *group, bool hasTex)
 	     it != itend; ++it)
 	{
 		mesh->mat[material_index] = (*it)->getMaterial();
-		material_index++;
 
 		vector<Strip*>& strips = (*it)->getStrips();
 		for (vector<Strip*>::const_iterator s = strips.begin(), send = strips.end(); s != send; ++s) {
@@ -811,6 +810,7 @@ void BlenderStrokeRenderer::GenerateStrokeMesh(StrokeGroup *group, bool hasTex)
 					// poly
 					polys->loopstart = loop_index;
 					polys->totloop = 3;
+					polys->mat_nr = material_index;
 					++polys;
 
 					// Even and odd loops connect triangles vertices differently
@@ -909,6 +909,7 @@ void BlenderStrokeRenderer::GenerateStrokeMesh(StrokeGroup *group, bool hasTex)
 				}
 			} // loop over strip vertices
 		} // loop over strips
+		material_index++;
 	} // loop over strokes
 
 	test_object_materials(freestyle_bmain, (ID *)mesh);