improved method of getting the tangent axis from a bmesh triangle,

rather then getting the longest edge, get the edge which which is most different from the 2 others ends up giving more useful results: for an isosceles triangle it returns the base weather its longer or shorter then the other sides.

1 files changed, 22 insertions, 2 deletions

diff --git a/source/blender/bmesh/intern/bmesh_marking.c b/source/blender/bmesh/intern/bmesh_marking.c
index 4e29756104a..73aee5917ae 100644
--- a/source/blender/bmesh/intern/bmesh_marking.c
+++ b/source/blender/bmesh/intern/bmesh_marking.c
@@ -710,8 +710,28 @@ void BM_editselection_plane(BMEditSelection *ese, float r_plane[3])
 			cross_v3_v3v3(r_plane, efa->no, vec);
 		}
 		else {
-			if (efa->len == 4) {
-				BMVert *verts[4] = {NULL};
+			if (efa->len == 3) {
+				BMVert *verts[3];
+				float lens[3];
+				float difs[3];
+				int  order[3] = {0, 1, 2};
+
+				BM_face_as_array_vert_tri(efa, verts);
+
+				lens[0] = len_v3v3(verts[0]->co, verts[1]->co);
+				lens[1] = len_v3v3(verts[1]->co, verts[2]->co);
+				lens[2] = len_v3v3(verts[2]->co, verts[0]->co);
+
+				/* find the shortest or the longest loop */
+				difs[0] = fabsf(lens[1] - lens[2]);
+				difs[1] = fabsf(lens[2] - lens[0]);
+				difs[2] = fabsf(lens[0] - lens[1]);
+
+				axis_sort_v3(difs, order);
+				sub_v3_v3v3(r_plane, verts[order[0]]->co, verts[(order[0] + 1) % 3]->co);
+			}
+			else if (efa->len == 4) {
+				BMVert *verts[4];
 				float vecA[3], vecB[3];
 
 				// BM_iter_as_array(NULL, BM_VERTS_OF_FACE, efa, (void **)verts, 4);