Fix T66802: Edge Slide: Unpredictable direction of the edge loop when it is fully occluded

When an edge loop is fully occluded the direction of movement
is not calculated resulting in unpredictable behavior.

So always calculate the direction of the groups of edge loops
but continue preventing occluded edges from affecting `mval_dir`
(global) value.

Differential Revision: https://developer.blender.org/D5247

1 files changed, 11 insertions, 7 deletions

diff --git a/source/blender/editors/transform/transform.c b/source/blender/editors/transform/transform.c
index c12821b321b..24efa33bdfa 100644
--- a/source/blender/editors/transform/transform.c
+++ b/source/blender/editors/transform/transform.c
@@ -6456,8 +6456,10 @@ static void calcEdgeSlide_mval_range(TransInfo *t,
       }
 
       /* This test is only relevant if object is not wire-drawn! See [#32068]. */
-      if (use_occlude_geometry &&
-          !BMBVH_EdgeVisible(bmbvh, e, t->depsgraph, ar, v3d, tc->obedit)) {
+      bool is_visible = !use_occlude_geometry ||
+                        BMBVH_EdgeVisible(bmbvh, e, t->depsgraph, ar, v3d, tc->obedit);
+
+      if (!is_visible && !use_calc_direction) {
         continue;
       }
 
@@ -6479,11 +6481,13 @@ static void calcEdgeSlide_mval_range(TransInfo *t,
 
       /* global direction */
       dist_sq = dist_squared_to_line_segment_v2(mval, sco_b, sco_a);
-      if ((dist_best_sq == -1.0f) ||
-          /* intentionally use 2d size on 3d vector */
-          (dist_sq < dist_best_sq && (len_squared_v2v2(sco_b, sco_a) > 0.1f))) {
-        dist_best_sq = dist_sq;
-        sub_v3_v3v3(mval_dir, sco_b, sco_a);
+      if (is_visible) {
+        if ((dist_best_sq == -1.0f) ||
+            /* intentionally use 2d size on 3d vector */
+            (dist_sq < dist_best_sq && (len_squared_v2v2(sco_b, sco_a) > 0.1f))) {
+          dist_best_sq = dist_sq;
+          sub_v3_v3v3(mval_dir, sco_b, sco_a);
+        }
       }
 
       if (use_calc_direction) {