Fix (unreported) EditNormal modifier: broken 'flip poly' feature.

Newly computed custom normals were forgotten during poly flipping, leading
to wrong custom normals being assigned to wrong loop...

Dead simple, but was tough to track down this one!

4 files changed, 16 insertions, 7 deletions

diff --git a/source/blender/blenkernel/BKE_mesh.h b/source/blender/blenkernel/BKE_mesh.h
index c7d5857b873..d8d869015a3 100644
--- a/source/blender/blenkernel/BKE_mesh.h
+++ b/source/blender/blenkernel/BKE_mesh.h
@@ -323,7 +323,7 @@ void BKE_mesh_mdisp_flip(struct MDisps *md, const bool use_loop_mdisp_flip);
 
 void BKE_mesh_polygon_flip_ex(
         struct MPoly *mpoly, struct MLoop *mloop, struct CustomData *ldata,
-        struct MDisps *mdisp, const bool use_loop_mdisp_flip);
+        float (*lnors)[3], struct MDisps *mdisp, const bool use_loop_mdisp_flip);
 void BKE_mesh_polygon_flip(struct MPoly *mpoly, struct MLoop *mloop, struct CustomData *ldata);
 void BKE_mesh_polygons_flip(struct MPoly *mpoly, struct MLoop *mloop, struct CustomData *ldata, int totpoly);
 
diff --git a/source/blender/blenkernel/intern/cdderivedmesh.c b/source/blender/blenkernel/intern/cdderivedmesh.c
index e7e6118813e..392a38773e7 100644
--- a/source/blender/blenkernel/intern/cdderivedmesh.c
+++ b/source/blender/blenkernel/intern/cdderivedmesh.c
@@ -2660,6 +2660,9 @@ void CDDM_calc_loop_normals(DerivedMesh *dm, const bool use_split_normals, const
 }
 
 /* #define DEBUG_CLNORS */
+#ifdef DEBUG_CLNORS
+#  include "BLI_linklist.h"
+#endif
 
 void CDDM_calc_loop_normals_spacearr(
         DerivedMesh *dm, const bool use_split_normals, const float split_angle, MLoopNorSpaceArray *r_lnors_spacearr)
diff --git a/source/blender/blenkernel/intern/mesh_evaluate.c b/source/blender/blenkernel/intern/mesh_evaluate.c
index 577a21285f8..1c86fbcfe8e 100644
--- a/source/blender/blenkernel/intern/mesh_evaluate.c
+++ b/source/blender/blenkernel/intern/mesh_evaluate.c
@@ -677,7 +677,7 @@ static void split_loop_nor_single_do(LoopSplitTaskDataCommon *common_data, LoopS
 	 */
 	copy_v3_v3(*lnor, polynors[mp_index]);
 
-	/* printf("BASIC: handling loop %d / edge %d / vert %d\n", ml_curr_index, ml_curr->e, ml_curr->v); */
+	/* printf("BASIC: handling loop %d / edge %d / vert %d / poly %d\n", ml_curr_index, ml_curr->e, ml_curr->v, mp_index); */
 
 	/* If needed, generate this (simple!) lnor space. */
 	if (lnors_spacearr) {
@@ -3262,14 +3262,14 @@ void BKE_mesh_mdisp_flip(MDisps *md, const bool use_loop_mdisp_flip)
  */
 void BKE_mesh_polygon_flip_ex(
         MPoly *mpoly, MLoop *mloop, CustomData *ldata,
-        MDisps *mdisp, const bool use_loop_mdisp_flip)
+        float (*lnors)[3], MDisps *mdisp, const bool use_loop_mdisp_flip)
 {
 	int loopstart = mpoly->loopstart;
 	int loopend = loopstart + mpoly->totloop - 1;
 	const bool loops_in_ldata = (CustomData_get_layer(ldata, CD_MLOOP) == mloop);
 
 	if (mdisp) {
-		for (int i = mpoly->loopstart; i <= loopend; i++) {
+		for (int i = loopstart; i <= loopend; i++) {
 			BKE_mesh_mdisp_flip(&mdisp[i], use_loop_mdisp_flip);
 		}
 	}
@@ -3288,6 +3288,9 @@ void BKE_mesh_polygon_flip_ex(
 		if (!loops_in_ldata) {
 			SWAP(MLoop, mloop[loopstart], mloop[loopend]);
 		}
+		if (lnors) {
+			swap_v3_v3(lnors[loopstart], lnors[loopend]);
+		}
 		CustomData_swap(ldata, loopstart, loopend);
 	}
 	/* Even if we did not swap the other 'pivot' loop, we need to set its swapped edge. */
@@ -3299,7 +3302,7 @@ void BKE_mesh_polygon_flip_ex(
 void BKE_mesh_polygon_flip(MPoly *mpoly, MLoop *mloop, CustomData *ldata)
 {
 	MDisps *mdisp = CustomData_get_layer(ldata, CD_MDISPS);
-	BKE_mesh_polygon_flip_ex(mpoly, mloop, ldata, mdisp, true);
+	BKE_mesh_polygon_flip_ex(mpoly, mloop, ldata, NULL, mdisp, true);
 }
 
 /**
@@ -3315,7 +3318,7 @@ void BKE_mesh_polygons_flip(
 	int i;
 
 	for (mp = mpoly, i = 0; i < totpoly; mp++, i++) {
-		BKE_mesh_polygon_flip_ex(mp, mloop, ldata, mdisp, true);
+		BKE_mesh_polygon_flip_ex(mp, mloop, ldata, NULL, mdisp, true);
 	}
 }
 
diff --git a/source/blender/modifiers/intern/MOD_normal_edit.c b/source/blender/modifiers/intern/MOD_normal_edit.c
index d386653d2c6..2cfa746ab3c 100644
--- a/source/blender/modifiers/intern/MOD_normal_edit.c
+++ b/source/blender/modifiers/intern/MOD_normal_edit.c
@@ -158,6 +158,7 @@ static bool polygons_check_flip(
         MPoly *mpoly, float (*polynors)[3], const int num_polys)
 {
 	MPoly *mp;
+	MDisps *mdisp = CustomData_get_layer(ldata, CD_MDISPS);
 	int i;
 	bool flipped = false;
 
@@ -176,7 +177,7 @@ static bool polygons_check_flip(
 
 		/* If average of new loop normals is opposed to polygon normal, flip polygon. */
 		if (dot_v3v3(polynors[i], norsum) < 0.0f) {
-			BKE_mesh_polygon_flip(mp, mloop, ldata);
+			BKE_mesh_polygon_flip_ex(mp, mloop, ldata, nos, mdisp, true);
 			negate_v3(polynors[i]);
 			flipped = true;
 		}
@@ -272,6 +273,8 @@ static void normalEditModifier_do_radial(
 
 	if (polygons_check_flip(mloop, nos, dm->getLoopDataLayout(dm), mpoly, polynors, num_polys)) {
 		dm->dirty |= DM_DIRTY_TESS_CDLAYERS;
+		/* We need to recompute vertex normals! */
+		dm->calcNormals(dm);
 	}
 
 	BKE_mesh_normals_loop_custom_set(mvert, num_verts, medge, num_edges, mloop, nos, num_loops,