Fix T38409: Snapping Bug

Issue partially caused by own errors (glicth in new BKE_boundbox_ray_hit_check() code causing segfault in volume snapping,
and we have to treat ortho and persp differently in case of face snapping, because in persp our ray_start might very well
already be *inside* the boundbox of the checked object), and partly due to the fact that ED_view3d_win_to_vector()
was returning wrong vector (negated one) for ortho views (see previous commit).

1 files changed, 21 insertions, 11 deletions

diff --git a/source/blender/editors/transform/transform_snap.c b/source/blender/editors/transform/transform_snap.c
index 91f8da1d2ae..a51ed85913e 100644
--- a/source/blender/editors/transform/transform_snap.c
+++ b/source/blender/editors/transform/transform_snap.c
@@ -1519,10 +1519,10 @@ static bool snapDerivedMesh(short snap_mode, ARegion *ar, Object *ob, DerivedMes
 		invert_m4_m4(imat, obmat);
 		copy_m3_m4(timat, imat);
 		transpose_m3(timat);
-		
+
 		copy_v3_v3(ray_start_local, ray_start);
 		copy_v3_v3(ray_normal_local, ray_normal);
-		
+
 		mul_m4_v3(imat, ray_start_local);
 		mul_mat3_m4_v3(imat, ray_normal_local);
 
@@ -1536,20 +1536,30 @@ static bool snapDerivedMesh(short snap_mode, ARegion *ar, Object *ob, DerivedMes
 			{
 				BVHTreeRayHit hit;
 				BVHTreeFromMesh treeData;
-				float ray_org_local[3], local_scale;
-
-				copy_v3_v3(ray_org_local, ray_origin);
-				mul_m4_v3(imat, ray_org_local);
+				float local_scale;
 
 				/* local scale in normal direction */
 				local_scale = normalize_v3(ray_normal_local);
 
-				/* We pass a temp ray_start, set from object's boundbox, to avoid precision issues with very far
-				 * away ray_start values (as returned in case of ortho view3d), see T38358.
+				/* Only use closer ray_start in case of ortho view! In perspective one, ray_start may already
+				 * been *inside* boundbox, leading to snap failures (see T38409).
 				 */
-				len_diff -= local_scale;  /* make temp start point a bit away from bbox hit point. */
-				madd_v3_v3v3fl(ray_start_local, ray_org_local, ray_normal_local,
-				               len_v3v3(ray_start_local, ray_org_local) - len_diff);
+				if (!((RegionView3D *)ar->regiondata)->is_persp) {
+					float ray_org_local[3];
+
+					copy_v3_v3(ray_org_local, ray_origin);
+					mul_m4_v3(imat, ray_org_local);
+
+					/* We pass a temp ray_start, set from object's boundbox, to avoid precision issues with very far
+					 * away ray_start values (as returned in case of ortho view3d), see T38358.
+					 */
+					len_diff -= local_scale;  /* make temp start point a bit away from bbox hit point. */
+					madd_v3_v3v3fl(ray_start_local, ray_org_local, ray_normal_local,
+					               len_v3v3(ray_start_local, ray_org_local) - len_diff);
+				}
+				else {
+					len_diff = 0.0f;
+				}
 
 				treeData.em_evil = em;
 				bvhtree_from_mesh_faces(&treeData, dm, 0.0f, 4, 6);