UI: Hide & shrink scroll-bars based on cursor position

Scroll-bars are now hidden unless the cursor approaches them, in which case they
smoothly grow and become more & more visible. Note that since 0d309144020168e55,
scroll-bars are drawn on top of editor contents. There's no more jumping of
buttons when scroll-bars appear.

Technical notes:
* AZones are used to adjust scrollbars based on mouse movements

  We may want to support screen level AZones if we want scrollbars to also
  smoothly appear when approaching them from a different area.
  I also plan to make further changes to AZones to clean up stuff a bit.
* Had to move AZone handling to a post ARegion init stage, since we need the
  updated View2D data from there.
* View2D masks and scroller rectangles are now updated on every redraw. It's
  cheap to do that though.

1 files changed, 2 insertions, 0 deletions

diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index a042e42775b..96e3f4704d9 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -6382,6 +6382,8 @@ static void direct_link_region(FileData *fd, ARegion *ar, int spacetype)
 	ar->v2d.tab_num = 0;
 	ar->v2d.tab_cur = 0;
 	ar->v2d.sms = NULL;
+	ar->v2d.alpha_hor = ar->v2d.alpha_vert = 0;
+	ar->v2d.size_hor = ar->v2d.size_vert = 0;
 	BLI_listbase_clear(&ar->panels_category);
 	BLI_listbase_clear(&ar->handlers);
 	BLI_listbase_clear(&ar->uiblocks);