Fix T58450: Skin modifier not working if applied after subsurf

Referenced by issue #58450, Skin modifier not working if applied after subsurf

source/blender/blenkernel/intern/customdata.c

@@ -1194,6 +1194,12 @@ static void layerDefault_mvert_skin(void *data, int count)
 	}
 }
 
+static void layerCopy_mvert_skin(const void *source, void *dest,
+                                 int count)
+{
+	memcpy(dest, source, sizeof (MVertSkin) * count);
+}
+
 static void layerInterp_mvert_skin(
         const void **sources, const float *weights,
         const float *UNUSED(sub_weights),
@@ -1342,7 +1348,7 @@ static const LayerTypeInfo LAYERTYPEINFO[CD_NUMTYPES] = {
 	{sizeof(GridPaintMask), "GridPaintMask", 1, NULL, layerCopy_grid_paint_mask,
 	 layerFree_grid_paint_mask, NULL, NULL, NULL},
 	/* 36: CD_MVERT_SKIN */
-	{sizeof(MVertSkin), "MVertSkin", 1, NULL, NULL, NULL,
+	{sizeof(MVertSkin), "MVertSkin", 1, NULL, layerCopy_mvert_skin, NULL,
 	 layerInterp_mvert_skin, NULL, layerDefault_mvert_skin},
 	/* 37: CD_FREESTYLE_EDGE */
 	{sizeof(FreestyleEdge), "FreestyleEdge", 1, NULL, NULL, NULL, NULL, NULL, NULL},

source/blender/blenkernel/intern/subdiv_mesh.c

@@ -1032,6 +1032,41 @@ static void points_for_loose_edges_interpolation_get(
 	}
 }
 
+static void subdiv_mesh_vertex_of_loose_edge_interpolate(
+        SubdivMeshContext *ctx,
+        const MEdge *coarse_edge,
+        const float u,
+        const int subdiv_vertex_index)
+{
+	const Mesh *coarse_mesh = ctx->coarse_mesh;
+	Mesh *subdiv_mesh = ctx->subdiv_mesh;
+	if (u == 0.0f) {
+		CustomData_copy_data(&coarse_mesh->vdata,
+		                     &subdiv_mesh->vdata,
+		                     coarse_edge->v1,
+		                     subdiv_vertex_index,
+		                     1);
+	}
+	else if (u == 1.0f) {
+		CustomData_copy_data(&coarse_mesh->vdata,
+		                     &subdiv_mesh->vdata,
+		                     coarse_edge->v2,
+		                     subdiv_vertex_index,
+		                     1);
+	}
+	else {
+		BLI_assert(u > 0.0f);
+		BLI_assert(u < 1.0f);
+		const float interpolation_weights[2] = {1.0f - u, u};
+		const int coarse_vertex_indices[2] = {coarse_edge->v1, coarse_edge->v2};
+		CustomData_interp(&coarse_mesh->vdata,
+		                  &subdiv_mesh->vdata,
+		                  coarse_vertex_indices,
+		                  interpolation_weights, NULL,
+		                  2, subdiv_vertex_index);
+	}
+}
+
 static void subdiv_mesh_vertex_of_loose_edge(
         const struct SubdivForeachContext *foreach_context,
         void *UNUSED(tls),
@@ -1055,6 +1090,10 @@ static void subdiv_mesh_vertex_of_loose_edge(
 	float weights[4];
 	key_curve_position_weights(u, weights, KEY_BSPLINE);
 
+	/* Interpolate custom data. */
+	subdiv_mesh_vertex_of_loose_edge_interpolate(
+	        ctx, coarse_edge, u, subdiv_vertex_index);
+	/* Initialize  */
 	MVert *subdiv_vertex = &subdiv_mvert[subdiv_vertex_index];
 	interp_v3_v3v3v3v3(subdiv_vertex->co,
 	                   points[0],
@@ -1064,11 +1103,12 @@ static void subdiv_mesh_vertex_of_loose_edge(
 	                   weights);
 	/* Reset flags and such. */
 	subdiv_vertex->flag = 0;
+	/* TODO(sergey): This matches old behavior, but we can as well interpolate
+	 * it. Maybe even using vertex varying attributes. */
 	subdiv_vertex->bweight = 0.0f;
-	/* Reset normal. */
-	subdiv_vertex->no[0] = 0.0f;
-	subdiv_vertex->no[1] = 0.0f;
-	subdiv_vertex->no[2] = 1.0f;
+	/* Reset normal, initialize it in a similar way as edit mode does for a
+	 * vertices adjacent to a loose edges. */
+	normal_float_to_short_v3(subdiv_vertex->no, subdiv_vertex->co);
 }
 
 /* =============================================================================

source/blender/modifiers/intern/MOD_skin.c

@@ -859,6 +859,7 @@ static Mesh *subdivide_base(Mesh *orig)
 	for (i = 0, totsubd = 0; i < totorigedge; i++) {
 		edge_subd[i] += calc_edge_subdivisions(origvert, orignode,
 		                                       &origedge[i], degree);
+		BLI_assert(edge_subd[i] >= 0);
 		totsubd += edge_subd[i];
 	}