Fix for persistent failures of BLI_assert(CustomData_has_layer(&dm->faceData, CD_POLYINDEX));

in CDDM_calc_normals_mapping_ex() in source/blender/blenkernel/intern/cdderivedmesh.c.
Problem report by flokkievids with an example .blend file for reproducing the issue. Thanks!

The issue was caused by the fact that Freestyle was using the pre-BMesh way for constructing
mesh data with the aim of generating a temporary 3D scene for stroke rendering.  Specifically,
the MFace struct was used for defining triangular faces.  Now BMesh is in the trunk, MFace
is internally used for tessellated faces only, and MPoly and MLoop are used for general mesh
data construction.  This commit is intended to update the Freestyle stroke rendering code in
the BMesh way.

source/blender/freestyle/intern/blender_interface/BlenderStrokeRenderer.cpp

@@ -23,6 +23,7 @@ extern "C" {
 #include "BKE_library.h" /* free_libblock */
 #include "BKE_material.h"
 #include "BKE_main.h" /* struct Main */
+#include "BKE_mesh.h"
 #include "BKE_object.h"
 #include "BKE_scene.h"
 
@@ -178,7 +179,7 @@ void BlenderStrokeRenderer::RenderStrokeRepBasic(StrokeRep *iStrokeRep) const{
 	  Strip::vertex_container::iterator v[3];
 	  StrokeVertexRep *svRep[3];
 	  Vec3r color[3];
-	  unsigned int vertex_index;
+	  unsigned int vertex_index, edge_index, loop_index;
 	  Vec2r p;
 	
 	  for(vector<Strip*>::iterator s=strips.begin(), send=strips.end();
@@ -187,7 +188,7 @@ void BlenderStrokeRenderer::RenderStrokeRepBasic(StrokeRep *iStrokeRep) const{
 		
 	    Strip::vertex_container& strip_vertices = (*s)->vertices();
 		int strip_vertex_count = (*s)->sizeStrip();
-		int m, n, visible_faces, visible_segments;
+		int xl, xu, yl, yu, n, visible_faces, visible_segments;
 		bool visible;
 
 		// iterate over all vertices and count visible faces and strip segments
@@ -203,13 +204,13 @@ void BlenderStrokeRenderer::RenderStrokeRepBasic(StrokeRep *iStrokeRep) const{
 			svRep[0] = *(v[0]);
 			svRep[1] = *(v[1]);
 			svRep[2] = *(v[2]);
-			m = 0;
+			xl = xu = yl = yu = 0;
 			for (int j = 0; j < 3; j++) {
 				p = svRep[j]->point2d();
-				if (p[0] < 0.0 || p[0] > _width || p[1] < 0.0 || p[1] > _height)
-					m++;
+				if (p[0] < 0.0) xl++; else if (p[0] > _width) xu++;
+				if (p[1] < 0.0) yl++; else if (p[1] > _height) yu++;
 			}
-			if (m == 3) {
+			if (xl == 3 || xu == 3 || yl == 3 || yu == 3) {
 				visible = false;
 			} else {
 				visible_faces++;
@@ -244,56 +245,74 @@ void BlenderStrokeRenderer::RenderStrokeRepBasic(StrokeRep *iStrokeRep) const{
 		mesh->totvert = visible_faces + visible_segments * 2;
 		mesh->mvert = (MVert*) CustomData_add_layer( &mesh->vdata, CD_MVERT, CD_CALLOC, NULL, mesh->totvert);
 			
-		// faces allocation
-		mesh->totface = visible_faces;
-		mesh->mface = (MFace*) CustomData_add_layer( &mesh->fdata, CD_MFACE, CD_CALLOC, NULL, mesh->totface);
+		// edges allocation
+		mesh->totedge = visible_faces * 2 + visible_segments;
+		mesh->medge = (MEdge*) CustomData_add_layer( &mesh->edata, CD_MEDGE, CD_CALLOC, NULL, mesh->totedge);
 
-		// colors allocation  - me.vertexColors = True
-		mesh->mcol = (MCol *) CustomData_add_layer( &mesh->fdata, CD_MCOL, CD_CALLOC, NULL, mesh->totface );
+		// faces allocation
+		mesh->totpoly = visible_faces;
+		mesh->mpoly= (MPoly*) CustomData_add_layer( &mesh->pdata, CD_MPOLY, CD_CALLOC, NULL, mesh->totpoly);
+
+		// loops allocation
+		mesh->totloop = visible_faces * 3;
+		mesh->mloop= (MLoop*) CustomData_add_layer( &mesh->ldata, CD_MLOOP, CD_CALLOC, NULL, mesh->totloop);
+		
+		// colors allocation
+		mesh->mloopcol = (MLoopCol *) CustomData_add_layer( &mesh->ldata, CD_MLOOPCOL, CD_CALLOC, NULL, mesh->totloop);
 
 		////////////////////
 		//  Data copy
 		////////////////////
 		
 		MVert* vertices = mesh->mvert;
-		MFace* faces = mesh->mface;
-		MCol* colors = mesh->mcol;
+		MEdge* edges = mesh->medge;
+		MPoly* polys = mesh->mpoly;
+		MLoop* loops = mesh->mloop;
+		MLoopCol* colors = mesh->mloopcol;
 
-	    v[0] = strip_vertices.begin();
+		v[0] = strip_vertices.begin();
 	    v[1] = v[0]; ++(v[1]);
 	    v[2] = v[1]; ++(v[2]);
 
-		vertex_index = 0;
+		vertex_index = edge_index = loop_index = 0;
 		visible = false;
 
-	    for (n = 2; n < strip_vertex_count; n++)
+		// Note: Mesh generation in the following loop assumes stroke strips
+		// to be triangle strips.
+		for (n = 2; n < strip_vertex_count; n++)
 		{
 			svRep[0] = *(v[0]);
 			svRep[1] = *(v[1]);
 			svRep[2] = *(v[2]);
-			m = 0;
+			xl = xu = yl = yu = 0;
 			for (int j = 0; j < 3; j++) {
 				p = svRep[j]->point2d();
-				if (p[0] < 0.0 || p[0] > _width || p[1] < 0.0 || p[1] > _height)
-					m++;
+				if (p[0] < 0.0) xl++; else if (p[0] > _width) xu++;
+				if (p[1] < 0.0) yl++; else if (p[1] > _height) yu++;
 			}
-			if (m == 3) {
+			if (xl == 3 || xu == 3 || yl == 3 || yu == 3) {
 				visible = false;
 			} else {
 				if (!visible) {
-					vertex_index += 2;
-
 					// first vertex
 					vertices->co[0] = svRep[0]->point2d()[0];
 					vertices->co[1] = svRep[0]->point2d()[1];
 					vertices->co[2] = get_stroke_vertex_z();
 					++vertices;
+					++vertex_index;
 					
 					// second vertex
 					vertices->co[0] = svRep[1]->point2d()[0];
 					vertices->co[1] = svRep[1]->point2d()[1];
 					vertices->co[2] = get_stroke_vertex_z();
 					++vertices;
+					++vertex_index;
+
+					// first edge
+					edges->v1 = vertex_index - 2;
+					edges->v2 = vertex_index - 1;
+					++edges;
+					++edge_index;
 				}
 				visible = true;
 
@@ -301,43 +320,89 @@ void BlenderStrokeRenderer::RenderStrokeRepBasic(StrokeRep *iStrokeRep) const{
 				vertices->co[0] = svRep[2]->point2d()[0];
 				vertices->co[1] = svRep[2]->point2d()[1];
 				vertices->co[2] = get_stroke_vertex_z();
+				++vertices;
+				++vertex_index;
 
-				// faces
-				faces->v1 = vertex_index - 2;
-				faces->v2 = vertex_index - 1;
-				faces->v3 = vertex_index;
-				faces->v4 = 0;
+				// edges
+				edges->v1 = vertex_index - 1;
+				edges->v2 = vertex_index - 3;
+				++edges;
+				++edge_index;
+
+				edges->v1 = vertex_index - 1;
+				edges->v2 = vertex_index - 2;
+				++edges;
+				++edge_index;
+
+				// poly
+				polys->loopstart = loop_index;
+				polys->totloop = 3;
+				++polys;
+
+				// loops
+				if (n % 2 == 0) {
+					loops[0].v = vertex_index - 1;
+					loops[0].e = edge_index - 1;
+
+					loops[1].v = vertex_index - 2;
+					loops[1].e = edge_index - 3;
+
+					loops[2].v = vertex_index - 3;
+					loops[2].e = edge_index - 2;
+				} else {
+					loops[0].v = vertex_index - 1;
+					loops[0].e = edge_index - 2;
+
+					loops[1].v = vertex_index - 3;
+					loops[1].e = edge_index - 3;
+
+					loops[2].v = vertex_index - 2;
+					loops[2].e = edge_index - 1;
+				}
+				loops += 3;
+				loop_index += 3;
 
 				// colors
-				// red and blue are swapped - cf DNA_meshdata_types.h : MCol	
-				color[0] = svRep[0]->color();
-				color[1] = svRep[1]->color();
-				color[2] = svRep[2]->color();
+				if (n % 2 == 0) {
+					colors[0].r = (short)(255.0f*svRep[2]->color()[0]);
+					colors[0].g = (short)(255.0f*svRep[2]->color()[1]);
+					colors[0].b = (short)(255.0f*svRep[2]->color()[2]);
+					colors[0].a = (short)(255.0f*svRep[2]->alpha());
 					
-				colors->r = (short)(255.0f*(color[0])[2]);
-				colors->g = (short)(255.0f*(color[0])[1]);
-				colors->b = (short)(255.0f*(color[0])[0]);
-				colors->a = (short)(255.0f*svRep[0]->alpha());
-				++colors;
+					colors[1].r = (short)(255.0f*svRep[1]->color()[0]);
+					colors[1].g = (short)(255.0f*svRep[1]->color()[1]);
+					colors[1].b = (short)(255.0f*svRep[1]->color()[2]);
+					colors[1].a = (short)(255.0f*svRep[1]->alpha());
 					
-				colors->r = (short)(255.0f*(color[1])[2]);
-				colors->g = (short)(255.0f*(color[1])[1]);
-				colors->b = (short)(255.0f*(color[1])[0]);
-				colors->a = (short)(255.0f*svRep[1]->alpha());
-				++colors;
+					colors[2].r = (short)(255.0f*svRep[0]->color()[0]);
+					colors[2].g = (short)(255.0f*svRep[0]->color()[1]);
+					colors[2].b = (short)(255.0f*svRep[0]->color()[2]);
+					colors[2].a = (short)(255.0f*svRep[0]->alpha());
+				} else {
+					colors[0].r = (short)(255.0f*svRep[2]->color()[0]);
+					colors[0].g = (short)(255.0f*svRep[2]->color()[1]);
+					colors[0].b = (short)(255.0f*svRep[2]->color()[2]);
+					colors[0].a = (short)(255.0f*svRep[2]->alpha());
 					
-				colors->r = (short)(255.0f*(color[2])[2]);
-				colors->g = (short)(255.0f*(color[2])[1]);
-				colors->b = (short)(255.0f*(color[2])[0]);
-				colors->a = (short)(255.0f*svRep[2]->alpha());
-				++colors;
+					colors[1].r = (short)(255.0f*svRep[0]->color()[0]);
+					colors[1].g = (short)(255.0f*svRep[0]->color()[1]);
+					colors[1].b = (short)(255.0f*svRep[0]->color()[2]);
+					colors[1].a = (short)(255.0f*svRep[0]->alpha());
+					
+					colors[2].r = (short)(255.0f*svRep[1]->color()[0]);
+					colors[2].g = (short)(255.0f*svRep[1]->color()[1]);
+					colors[2].b = (short)(255.0f*svRep[1]->color()[2]);
+					colors[2].a = (short)(255.0f*svRep[1]->alpha());
+				}
+				colors += 3;
 
-				++faces; ++vertices; ++colors;
-				++vertex_index;
 			}
 			++v[0]; ++v[1]; ++v[2];
 
 		} // loop over strip vertices 
+#if 0
+		BKE_mesh_validate(mesh, TRUE);
+#endif
 
 	} // loop over strips