This patch does several things. Sorry.
In BuildDisplayList implementations, instead of wrapping display items in nsDisplayClip, we
push clip state onto the nsDisplayListBuilder and give the display items an
explicit clip when they're created.
In FrameLayerBuilder, we use the explicit clips we find on display items instead of
computing our own.
We remove nsDisplayClip and everything that depends on it.
We remove ExplodeAnonymousChildLists. With nsDisplayClip gone, and
nsDisplayOptionEventGrabber removed in a previous patch, there are no
anonymous child lists.
nsDisplayItem::TryMerge implementations need to make sure they have the same
clip before being merged.
I ripped out the part of PruneDisplayListForExtraPage that adjusts clip rects.
As far as I can tell, it isn't actually necessary.
--HG--
extra : rebase_source : 6f3988b385d0ac54ab26fad10b12173884441f48
Renames GetList to GetSameCoordinateSystemChildren, and adds an assertion
to verify that the children have the same reference frame as the parent.
Adds nsDisplayList::GetChildren to return whatever children there are.
Obsoletes nsDisplayTransform::GetStoredList.
Currently we return an extra out parameter on GetOpaqueRegion. This is ugly and it's also going to be inefficient
because in a followup patch I'm going to avoid calls to GetOpaqueRegion, but we still need to know whether the item
needs a transparent surface. So this patch removes that out parameter. Instead, we rely on the fact that only
Windows' glass-window-background display item needs to force a transparent surface, and there can only be one
of those per window. So we store a reference to it in the nsDisplayListBuilder if there is one, and then we can
efficiently tell if any leaf display item is the one that forces a transparent surface. For display items that
wrap a list, we continue to store whether they need to force a transparent surface in a boolean in the list.
Previously we snapped the results of nsDisplayItem::GetBounds and
nsDisplayItem::GetOpaqueRegion internally. By tracking which display items were
inside transforms, we disabled snapping quite conservatively whenever an ancestor
had a transform, which is undesirable.
With this patch, we don't snap inside GetBounds or GetOpaqueRegion, but just return
a boolean flag indicating whether the item will draw with snapping or not. This flag
is conservative so that "true" means we will snap (if the graphics context has a transform
that allows snapping), but "false" means we might or might not snap (so it's always safe
to return false).
FrameLayerBuilder takes over responsibility for snapping item bounds. When it converts
display item bounds to layer pixel coordinates, it checks the snap flag returned from
the display item and checks whether the transform when we draw into the layer will be
a known scale (the ContainerParameters scale factors) plus integer translation. If both
are true, we snap the item bounds when converting to layer pixel coordinates. With
this approach, we can snap item bounds even when the items have ancestors with active
transforms.
