fix [#30583] very old blend files are loading post-bmesh with no face/uv information, just wires

versioning code called a customdata update function which ended up clearing tessfaces - before converting polygons to tessfaces.
Added check so tessfaces aren't cleared when there are no polygons.

1 files changed, 24 insertions, 16 deletions

diff --git a/source/blender/blenkernel/intern/mesh.c b/source/blender/blenkernel/intern/mesh.c
index 52dc3ff8d84..e376134b26b 100644
--- a/source/blender/blenkernel/intern/mesh.c
+++ b/source/blender/blenkernel/intern/mesh.c
@@ -305,26 +305,34 @@ const char *mesh_cmp(Mesh *me1, Mesh *me2, float thresh)
 
 static void mesh_ensure_tessellation_customdata(Mesh *me)
 {
-	const int tottex_original = CustomData_number_of_layers(&me->pdata, CD_MTEXPOLY);
-	const int totcol_original = CustomData_number_of_layers(&me->ldata, CD_MLOOPCOL);
+	if (UNLIKELY((me->totface != 0) && (me->totpoly == 0))) {
+		/* Pass, otherwise this function  clears 'mface' before
+		 * versioning 'mface -> mpoly' code kicks in [#30583]
+		 *
+		 * Callers could also check but safer to do here - campbell */
+	}
+	else {
+		const int tottex_original = CustomData_number_of_layers(&me->pdata, CD_MTEXPOLY);
+		const int totcol_original = CustomData_number_of_layers(&me->ldata, CD_MLOOPCOL);
 
-	const int tottex_tessface = CustomData_number_of_layers(&me->fdata, CD_MTFACE);
-	const int totcol_tessface = CustomData_number_of_layers(&me->fdata, CD_MCOL);
+		const int tottex_tessface = CustomData_number_of_layers(&me->fdata, CD_MTFACE);
+		const int totcol_tessface = CustomData_number_of_layers(&me->fdata, CD_MCOL);
 
-	if (tottex_tessface != tottex_original ||
-	    totcol_tessface != totcol_original )
-	{
-		BKE_mesh_tessface_clear(me);
+		if (tottex_tessface != tottex_original ||
+		    totcol_tessface != totcol_original )
+		{
+			BKE_mesh_tessface_clear(me);
 
-		CustomData_from_bmeshpoly(&me->fdata, &me->pdata, &me->ldata, me->totface);
+			CustomData_from_bmeshpoly(&me->fdata, &me->pdata, &me->ldata, me->totface);
 
-		/* note: this warning may be un-called for if we are inirializing the mesh for the
-		 * first time from bmesh, rather then giving a warning about this we could be smarter
-		 * and check if there was any data to begin with, for now just print the warning with
-		 * some info to help troubleshoot whats going on - campbell */
-		printf("%s: warning! Tessellation uvs or vcol data got out of sync, "
-		       "had to reset!\n    CD_MTFACE: %d != CD_MTEXPOLY: %d || CD_MCOL: %d != CD_MLOOPCOL: %d\n",
-		       __func__, tottex_tessface, tottex_original, totcol_tessface, totcol_original);
+			/* note: this warning may be un-called for if we are inirializing the mesh for the
+			 * first time from bmesh, rather then giving a warning about this we could be smarter
+			 * and check if there was any data to begin with, for now just print the warning with
+			 * some info to help troubleshoot whats going on - campbell */
+			printf("%s: warning! Tessellation uvs or vcol data got out of sync, "
+			       "had to reset!\n    CD_MTFACE: %d != CD_MTEXPOLY: %d || CD_MCOL: %d != CD_MLOOPCOL: %d\n",
+			       __func__, tottex_tessface, tottex_original, totcol_tessface, totcol_original);
+		}
 	}
 }