This guarantees that the animated geometry root for an item is always in the
same display list coordinate system as the frame.
--HG--
extra : rebase_source : 974434342459b76d62d89fdc04c22c518bf0c58b
This has two desirable side effects. The first and more important is that it prevents a scrollbar item from sitting between scroll layer items and preventing them from merging into one and thus preventing the creation of an async scrollable layer. The second is that scrollbars should be on top of the content they are scrolling in general, and this will make that happen in more cases.
This guarantees that the animated geometry root for an item is always in the
same display list coordinate system as the frame.
--HG--
extra : rebase_source : 249fd847a2c08f8d0846d698cce9dd4681e38a98
The content they contain may be moved, so any region that is opaquely covered at paint time may not be later.
This problem was made worse by bug 951467 because it made the bounds of the scroll layer item be the bounds of the scrollport is all cases (making it return wrong results even at paint time), instead of the bounds of the contained content (meaning the results would only be wrong after async scroll).
We incorrectly wrap abs pos items, but not wrapping them leads to too many sites failing to create scrollable layers that we can't do that. So instead just fix the clipping issue for now until a more robust solution can be developed.
The bounds of the scroll port match what will actually be drawn on the screen.
The bounds of the contained content (sized to the display port) are still accessible via mList.GetBounds, and similarly the visible rect of the contained content is mList.GetVisibleRect. The external bounds/visible rect are GetBounds and GetVisibleRect on the nsDisplayScrollLayer object itself.
We implement nsDisplayScrollInfoLayer::GetBounds solely so that it continues to return an empty rect because we expect active empty layers to have empty visible rects.
We no longer have to set our mVisibleRect in nsDisplayScrollLayer::ComputeVisibility because nsDisplayList::ComputeVisibilityForSublist now does it correctly for us (like other items).
We also have to teach ContainerState::ProcessDisplayItems to not set the visible region for scroll layers because it has the external visible region, not the larger internal display port sized visible region. We instead let BuildContainerLayer set the visible region of the layer.
APZC information is associated with layers, and having those layers suddenly
disappear because they became occluded, or their displayports are off-screen
has undesired effects.
This adds a new eCSSUnit_SharedList type for nsCSSValue, which is a
reference counted object that contains an nsCSSValueList. We need this
so that nsStyleDisplay::mSpecifiedTransform can hold a strong reference
to a specified transform list value. When 'transform' is specified
using a variable reference, the resulting nsCSSValue does not stick
around in the Declaration object, so we wouldn't be guaranteed that
it lives long enough for nsStyleDisplay to keep referencing it.
