Fix T40070, Bevel didn't bend as expected sometimes.

Two problems fixed. One, the comparison of angles to
'almost straight' or 'almost zero' needed a bigger epsilon.
Two, using the corner normal instead of the average face normal
is usually the right thing to do, and what the code was doing,
but in some cases the corner normal could be very wrong.

1 files changed, 20 insertions, 9 deletions

diff --git a/source/blender/bmesh/tools/bmesh_bevel.c b/source/blender/bmesh/tools/bmesh_bevel.c
index 3148f5c2d3c..d67dc07311e 100644
--- a/source/blender/bmesh/tools/bmesh_bevel.c
+++ b/source/blender/bmesh/tools/bmesh_bevel.c
@@ -54,6 +54,8 @@
 #define BEVEL_EPSILON_SQ 1e-12f
 #define BEVEL_EPSILON_BIG 1e-4f
 #define BEVEL_EPSILON_BIG_SQ 1e-8f
+#define BEVEL_EPSILON_ANG DEG2RADF(2.0f)
+#define BEVEL_SMALL_ANG DEG2RADF(10.0f)
 
 /* happens far too often, uncomment for development */
 // #define BEVEL_ASSERT_PROJECT
@@ -663,7 +665,7 @@ static bool point_between_edges(float co[3], BMVert *v, BMFace *f, EdgeHalf *e1,
 	cross_v3_v3v3(no, dir1, dirco);
 	if (dot_v3v3(no, f->no) < 0.0f)
 		ang1co = (float)(M_PI * 2.0) - ang1co;
-	return (ang11 - ang1co > -BEVEL_EPSILON_BIG);
+	return (ang11 - ang1co > -BEVEL_EPSILON_ANG);
 }
 
 /*
@@ -703,7 +705,7 @@ static void offset_meet(EdgeHalf *e1, EdgeHalf *e2, BMVert *v, BMFace *f, bool e
 	}
 
 	ang = angle_v3v3(dir1, dir2);
-	if (ang < BEVEL_EPSILON_BIG) {
+	if (ang < BEVEL_EPSILON_ANG) {
 		/* special case: e1 and e2 are parallel; put offset point perp to both, from v.
 		 * need to find a suitable plane.
 		 * if offsets are different, we're out of luck:
@@ -724,7 +726,7 @@ static void offset_meet(EdgeHalf *e1, EdgeHalf *e2, BMVert *v, BMFace *f, bool e
 			e2->offset_l = d;
 		copy_v3_v3(meetco, off1a);
 	}
-	else if (fabsf(ang - (float)M_PI) < BEVEL_EPSILON_BIG) {
+	else if (fabsf(ang - (float)M_PI) < BEVEL_EPSILON_ANG) {
 		/* special case e1 and e2 are antiparallel, so bevel is into
 		 * a zero-area face.  Just make the offset point on the
 		 * common line, at offset distance from v. */
@@ -738,10 +740,19 @@ static void offset_meet(EdgeHalf *e1, EdgeHalf *e2, BMVert *v, BMFace *f, bool e
 	else {
 		/* Get normal to plane where meet point should be,
 		 * using cross product instead of f->no in case f is non-planar.
+		 * Except: sometimes locally there can be a small angle
+		 * between dir1 and dir2 that leads to a normal that is actually almost
+		 * perpendicular to the face normal; in this case it looks wrong to use
+		 * the local (cross-product) normal, so use the face normal if the angle
+		 * between dir1 and dir2 is smallish.
 		 * If e1-v-e2 is a reflex angle (viewed from vertex normal side), need to flip.
 		 * Use f->no to figure out which side to look at angle from, as even if
 		 * f is non-planar, will be more accurate than vertex normal */
-		if (!edges_between) {
+		if (f && ang < BEVEL_SMALL_ANG) {
+			copy_v3_v3(norm_v1, f->no);
+			copy_v3_v3(norm_v2, f->no);
+		}
+		else if (!edges_between) {
 			cross_v3_v3v3(norm_v1, dir2, dir1);
 			normalize_v3(norm_v1);
 			if (dot_v3v3(norm_v1, f ? f->no : v->no) < 0.0f)
@@ -1162,7 +1173,7 @@ static bool make_unit_square_map(
 
 	sub_v3_v3v3(va_vmid, vmid, va);
 	sub_v3_v3v3(vb_vmid, vmid, vb);
-	if (fabsf(angle_v3v3(va_vmid, vb_vmid) - (float)M_PI) > 100.0f * BEVEL_EPSILON) {
+	if (fabsf(angle_v3v3(va_vmid, vb_vmid) - (float)M_PI) > BEVEL_EPSILON_ANG) {
 		sub_v3_v3v3(vo, va, vb_vmid);
 		cross_v3_v3v3(vddir, vb_vmid, va_vmid);
 		normalize_v3(vddir);
@@ -1508,8 +1519,8 @@ static bool eh_on_plane(EdgeHalf *e)
 
 	if (e->fprev && e->fnext) {
 		dot = dot_v3v3(e->fprev->no, e->fnext->no);
-		if (fabsf(dot) <= BEVEL_EPSILON ||
-		    fabsf(dot - 1.0f) <= BEVEL_EPSILON)
+		if (fabsf(dot) <= BEVEL_EPSILON_BIG ||
+		    fabsf(dot - 1.0f) <= BEVEL_EPSILON_BIG)
 		{
 			return true;
 		}
@@ -1919,7 +1930,7 @@ static BoundVert *pipe_test(BevVert *bv)
 			sub_v3_v3v3(dir3, BM_edge_other_vert(v3->ebev->e, bv->v)->co, bv->v->co);
 			normalize_v3(dir1);
 			normalize_v3(dir3);
-			if (angle_normalized_v3v3(dir1, dir3) < BEVEL_EPSILON_BIG) {
+			if (angle_normalized_v3v3(dir1, dir3) < BEVEL_EPSILON_ANG) {
 				epipe =  v1->ebev;
 				break;
 			}
@@ -1932,7 +1943,7 @@ static BoundVert *pipe_test(BevVert *bv)
 	/* check face planes: all should have normals perpendicular to epipe */
 	for (e = &bv->edges[0]; e != &bv->edges[bv->edgecount]; e++) {
 		if (e->fnext) {
-			if (dot_v3v3(dir1, e->fnext->no) > BEVEL_EPSILON)
+			if (dot_v3v3(dir1, e->fnext->no) > BEVEL_EPSILON_BIG)
 				return NULL;
 		}
 	}