BMesh: mesh-data picking, general improvements

Generalize logic for vert/edge/face selection:
- index cycling.
- selection bias with mixed modes.

Details:
- Edges now support index cycling (as verts/faces did already)
- Cycling over near elements is now only enabled when the mouse position remains the same.
- No longer do 2 selection passes to perform index cycling.

Fixes:
- Edges behind the view could be selected (surprising nobody reported!)
- Selection bias now only changes the element that gets picked without interning the return distance
  (was buggy with mixed modes).

1 files changed, 5 insertions, 7 deletions

diff --git a/source/blender/editors/space_view3d/view3d_draw.c b/source/blender/editors/space_view3d/view3d_draw.c
index 9fcdb77ef7f..a69a6be298e 100644
--- a/source/blender/editors/space_view3d/view3d_draw.c
+++ b/source/blender/editors/space_view3d/view3d_draw.c
@@ -1587,13 +1587,11 @@ unsigned int ED_view3d_backbuf_sample_rect(
 				if (*tbuf && *tbuf >= min && *tbuf < max) {
 					/* we got a hit */
 
-					/* get x,y pixel coords from the offset */
-					const float delta[2] = {
-					    ((tbuf - buf->rect) % size) - (size / 2),
-					    ((tbuf - buf->rect) / size) - (size / 2),
-					};
-
-					*r_dist = len_v2(delta);
+					/* get x,y pixel coords from the offset
+					 * (manhatten distance in keeping with other screen-based selection) */
+					*r_dist = (float)(
+					        abs(((tbuf - buf->rect) % size) - (size / 2)) +
+					        abs(((tbuf - buf->rect) / size) - (size / 2)));
 
 					/* indices start at 1 here */
 					index = (*tbuf - min) + 1;