Fix T46099: snapping failed on objects with some NULL-dimension in their bbox.

Added a helper that ensures a bbox has some non-NULL dimension along all its axes.

Also, fixed some (rather unlikely) NULL dereference cases (though it should not in this context,
`BKE_object_boundbox_get()` can return NULL).

3 files changed, 84 insertions, 4 deletions

diff --git a/source/blender/blenkernel/BKE_object.h b/source/blender/blenkernel/BKE_object.h
index 15ebfb54f41..6c5081d1ea9 100644
--- a/source/blender/blenkernel/BKE_object.h
+++ b/source/blender/blenkernel/BKE_object.h
@@ -143,6 +143,8 @@ bool BKE_boundbox_ray_hit_check(
 void BKE_boundbox_calc_center_aabb(const struct BoundBox *bb, float r_cent[3]);
 void BKE_boundbox_calc_size_aabb(const struct BoundBox *bb, float r_size[3]);
 void BKE_boundbox_minmax(const struct BoundBox *bb, float obmat[4][4], float r_min[3], float r_max[3]);
+struct BoundBox *BKE_boundbox_ensure_minimum_dimensions(
+        struct BoundBox *bb, struct BoundBox *bb_temp, const float epsilon);
 
 struct BoundBox *BKE_object_boundbox_get(struct Object *ob);
 void BKE_object_dimensions_get(struct Object *ob, float vec[3]);
diff --git a/source/blender/blenkernel/intern/object.c b/source/blender/blenkernel/intern/object.c
index fa20607ce30..526a71b477d 100644
--- a/source/blender/blenkernel/intern/object.c
+++ b/source/blender/blenkernel/intern/object.c
@@ -2665,6 +2665,66 @@ void BKE_boundbox_minmax(const BoundBox *bb, float obmat[4][4], float r_min[3],
 	}
 }
 
+/**
+ * Returns a BBox which each dimensions are at least epsilon.
+ * \note In case a given dimension needs to be enlarged, its final value will be in [epsilon, 3 * epsilon] range.
+ *
+ * \param bb the input bbox to check.
+ * \param bb_temp the temp bbox to modify (\a bb content is never changed).
+ * \param epsilon the minimum dimension to ensure.
+ * \return either bb (if nothing needed to be changed) or bb_temp.
+ */
+BoundBox *BKE_boundbox_ensure_minimum_dimensions(BoundBox *bb, BoundBox *bb_temp, const float epsilon)
+{
+	if (fabsf(bb->vec[0][0] - bb->vec[4][0]) < epsilon) {
+		/* Flat along X axis... */
+		*bb_temp = *bb;
+		bb = bb_temp;
+		bb->vec[0][0] -= epsilon;
+		bb->vec[1][0] -= epsilon;
+		bb->vec[2][0] -= epsilon;
+		bb->vec[3][0] -= epsilon;
+		bb->vec[4][0] += epsilon;
+		bb->vec[5][0] += epsilon;
+		bb->vec[6][0] += epsilon;
+		bb->vec[7][0] += epsilon;
+	}
+
+	if (fabsf(bb->vec[0][1] - bb->vec[3][1]) < epsilon) {
+		/* Flat along Y axis... */
+		if (bb != bb_temp) {
+			*bb_temp = *bb;
+			bb = bb_temp;
+		}
+		bb->vec[0][1] -= epsilon;
+		bb->vec[1][1] -= epsilon;
+		bb->vec[4][1] -= epsilon;
+		bb->vec[5][1] -= epsilon;
+		bb->vec[2][1] += epsilon;
+		bb->vec[3][1] += epsilon;
+		bb->vec[6][1] += epsilon;
+		bb->vec[7][1] += epsilon;
+	}
+
+	if (fabsf(bb->vec[0][2] - bb->vec[1][2]) < epsilon) {
+		/* Flat along Z axis... */
+		if (bb != bb_temp) {
+			*bb_temp = *bb;
+			bb = bb_temp;
+		}
+		bb->vec[0][2] -= epsilon;
+		bb->vec[3][2] -= epsilon;
+		bb->vec[4][2] -= epsilon;
+		bb->vec[7][2] -= epsilon;
+		bb->vec[1][2] += epsilon;
+		bb->vec[2][2] += epsilon;
+		bb->vec[5][2] += epsilon;
+		bb->vec[6][2] += epsilon;
+	}
+
+	return bb;
+}
+
 BoundBox *BKE_object_boundbox_get(Object *ob)
 {
 	BoundBox *bb = NULL;
diff --git a/source/blender/editors/transform/transform_snap.c b/source/blender/editors/transform/transform_snap.c
index 867e862017f..f6040732983 100644
--- a/source/blender/editors/transform/transform_snap.c
+++ b/source/blender/editors/transform/transform_snap.c
@@ -1527,8 +1527,17 @@ static bool snapDerivedMesh(short snap_mode, ARegion *ar, Object *ob, DerivedMes
 
 		if (do_bb) {
 			BoundBox *bb = BKE_object_boundbox_get(ob);
-			if (!BKE_boundbox_ray_hit_check(bb, ray_start_local, ray_normal_local, &len_diff)) {
-				return retval;
+
+			if (bb) {
+				BoundBox bb_temp;
+
+				/* We cannot aford a bbox with some null dimension, which may happen in some cases...
+				 * Threshold is rather high, but seems to be needed to get good behavior, see T46099. */
+				bb = BKE_boundbox_ensure_minimum_dimensions(bb, &bb_temp, 1e-1f);
+
+				if (!BKE_boundbox_ray_hit_check(bb, ray_start_local, ray_normal_local, &len_diff)) {
+					return retval;
+				}
 			}
 		}
 		else if (do_ray_start_correction) {
@@ -2151,8 +2160,17 @@ static bool peelDerivedMesh(
 		 * test against boundbox first
 		 * */
 		if (looptri_num > 16) {
-			struct BoundBox *bb = BKE_object_boundbox_get(ob);
-			test = BKE_boundbox_ray_hit_check(bb, ray_start_local, ray_normal_local, NULL);
+			BoundBox *bb = BKE_object_boundbox_get(ob);
+
+			if (bb) {
+				BoundBox bb_temp;
+
+				/* We cannot aford a bbox with some null dimension, which may happen in some cases...
+				 * Threshold is rather high, but seems to be needed to get good behavior, see T46099. */
+				bb = BKE_boundbox_ensure_minimum_dimensions(bb, &bb_temp, 1e-1f);
+
+				test = BKE_boundbox_ray_hit_check(bb, ray_start_local, ray_normal_local, NULL);
+			}
 		}
 		
 		if (test == true) {