Fix related to T46567: Skin modifier: add a warning message when no valid root vertex is found.

Otherwise user may have a hard time understanding why their modifier is no more working
after they e.g. deleted some vertices... including the root one. ;)

2 files changed, 11 insertions, 3 deletions

diff --git a/source/blender/blenkernel/intern/customdata.c b/source/blender/blenkernel/intern/customdata.c
index eb604275acc..f210d34d220 100644
--- a/source/blender/blenkernel/intern/customdata.c
+++ b/source/blender/blenkernel/intern/customdata.c
@@ -1303,7 +1303,7 @@ static const LayerTypeInfo LAYERTYPEINFO[CD_NUMTYPES] = {
 	/* 35: CD_GRID_PAINT_MASK */
 	{sizeof(GridPaintMask), "GridPaintMask", 1, NULL, layerCopy_grid_paint_mask,
 	 layerFree_grid_paint_mask, NULL, NULL, NULL},
-	/* 36: CD_SKIN_NODE */
+	/* 36: CD_MVERT_SKIN */
 	{sizeof(MVertSkin), "MVertSkin", 1, NULL, NULL, NULL,
 	 layerInterp_mvert_skin, NULL, layerDefault_mvert_skin},
 	/* 37: CD_FREESTYLE_EDGE */
diff --git a/source/blender/modifiers/intern/MOD_skin.c b/source/blender/modifiers/intern/MOD_skin.c
index 1b8b29666e2..9f1ec4de3d5 100644
--- a/source/blender/modifiers/intern/MOD_skin.c
+++ b/source/blender/modifiers/intern/MOD_skin.c
@@ -708,7 +708,8 @@ static EMat *build_edge_mats(const MVertSkin *vs,
                              int totvert,
                              const MEdge *medge,
                              const MeshElemMap *emap,
-                             int totedge)
+                             int totedge,
+                             bool *has_valid_root)
 {
 	BLI_Stack *stack;
 	EMat *emat;
@@ -736,6 +737,8 @@ static EMat *build_edge_mats(const MVertSkin *vs,
 					stack_elem.e = emap[v].indices[i];
 					BLI_stack_push(stack, &stack_elem);
 				}
+
+				*has_valid_root = true;
 			}
 		}
 	}
@@ -1828,6 +1831,7 @@ static DerivedMesh *base_skin(DerivedMesh *origdm,
 	MEdge *medge;
 	MDeformVert *dvert;
 	int totvert, totedge;
+	bool has_valid_root = false;
 
 	nodes = CustomData_get_layer(&origdm->vertData, CD_MVERT_SKIN);
 
@@ -1839,7 +1843,7 @@ static DerivedMesh *base_skin(DerivedMesh *origdm,
 
 	BKE_mesh_vert_edge_map_create(&emap, &emapmem, medge, totvert, totedge);
 
-	emat = build_edge_mats(nodes, mvert, totvert, medge, emap, totedge);
+	emat = build_edge_mats(nodes, mvert, totvert, medge, emap, totedge, &has_valid_root);
 	skin_nodes = build_frames(mvert, totvert, nodes, emap, emat);
 	MEM_freeN(emat);
 	emat = NULL;
@@ -1850,6 +1854,10 @@ static DerivedMesh *base_skin(DerivedMesh *origdm,
 	MEM_freeN(emap);
 	MEM_freeN(emapmem);
 
+	if (!has_valid_root) {
+		modifier_setError(&smd->modifier, "No valid root vertex found (you need one per mesh island you want to skin)");
+	}
+
 	if (!bm)
 		return NULL;