634360 - Allow non-rectangular displayport (pixel cache)

Status: NEW

(Core :: Graphics, defect)

Description

[Matt Brubeck (:mbrubeck)]

Bug 629025 points out that Fennec displays noticeable checkerboards when scrolling horizontally, because our displayport is taller than it is wide (to optimize vertical scrolling).

We could improve this by making the displayport wider, but this would increase memory use.  And most of the added memory would be wasted, because it would be in regions that are reachable only by scrolling diagonally (which is not easy or common in Fennec).

The optimal displayport might be shaped more like this, covering mostly areas that are reachable by just horizontal or just vertical panning:

     +--------+
     |        |
+----+--------+----+
|    |viewport|    |
|    |        |    |
+----+--------+----+
     |        |
     |        |
     |        |
     |        |
     +--------+

It might also be useful to cache some disjoint areas, like the top and bottom of the page (which are reachable via gestures and keyboard commands).