Gecko:DisplayListBasedInvalidation

Display List Based Invalidation - Bug 539356

Instead of invalidating areas of the screen as we do currently, we want invalidation to happen at the display list/layer boundary to reduce unnecessary redrawing

Basic Outline

• Display List changes
  • We want to compare the new display to the old one and invalidate layer regions of anything that has changed.
  • We already cache most of the information that we need, and iterate over it in FrameLayerBuilder.
    • We need to add the old bounds of the display item into the cached data
    • Some items (e.g. borders) need two rectangles: an outer rect and an inner rect
  • Invalidating display items that no longer exist.
    • How do we do this?
    • We could iterate over the frames DisplayItemData at the end of nsFrame::BuildDisplayList, and send invalidations for any display item types that weren't just created.
    • FrameLayerBuilder already detects items being added to or removed from a layer, so this won't be a problem if we do the processing in FrameLayerBuilder

• Style and other changes
  • These should invalidate all (?) display items for the frame, so we can just set a dirty bit on the frame and check this from FrameLayerBuilder

Potential Problems

• Window resizing / incremental loading
  • We want to make sure that we are only invalidating the new areas, not the entire page
• Bordered frame size changes
  • We don't really want to invalidate the entire area here, but we do need to invalidate some of the internal area as well as the extended bounds.