Change GetThebesLayerResolutionForFrame to GetThebesLayerScaleForFrame,
which just returns a scale. Ensure that the scale is as accurate as possible
even if dedicated layers for scrolled content (or any layers at all) have not
been created yet, by taking into account transforms that have not yet
generated layers. This makes the decisions made by
nsGfxScrollFrameInner::ScrollToImpl independent of whether there is
currently an active layer for the scrolled content (or much more nearly so).
In nsGfxScrollFrameInner::ScrollToImpl, do not use the current internal
fractional offset of the ThebesLayer, which is in a mostly unrelated
coordinate space to our scroll positions. Instead, just try to make sure
that the previous and next scroll position differ by a whole number of
layer pixels.
Change GetThebesLayerResolutionForFrame to GetThebesLayerScaleForFrame,
which just returns a scale. Ensure that the scale is as accurate as possible
even if dedicated layers for scrolled content (or any layers at all) have not
been created yet, by taking into account transforms that have not yet
generated layers. This makes the decisions made by
nsGfxScrollFrameInner::ScrollToImpl independent of whether there is
currently an active layer for the scrolled content (or much more nearly so).
In nsGfxScrollFrameInner::ScrollToImpl, do not use the current internal
fractional offset of the ThebesLayer, which is in a mostly unrelated
coordinate space to our scroll positions. Instead, just try to make sure
that the previous and next scroll position differ by a whole number of
layer pixels.
Change GetThebesLayerResolutionForFrame to GetThebesLayerScaleForFrame,
which just returns a scale. Ensure that the scale is as accurate as possible
even if dedicated layers for scrolled content (or any layers at all) have not
been created yet, by taking into account transforms that have not yet
generated layers. This makes the decisions made by
nsGfxScrollFrameInner::ScrollToImpl independent of whether there is
currently an active layer for the scrolled content (or much more nearly so).
In nsGfxScrollFrameInner::ScrollToImpl, do not use the current internal
fractional offset of the ThebesLayer, which is in a mostly unrelated
coordinate space to our scroll positions. Instead, just try to make sure
that the previous and next scroll position differ by a whole number of
layer pixels.
A comment in ApplyThebesLayerInvalidation says that it preserves the content
of ThebesLayerInvalidRegion, in case there are multiple container layers for
the same frame. SetHasContainerLayer, however, immediately clears said property.
This was causing invalidations to be lost since Bug 758620 on fixed-position
elements, as they were being separated out onto their own layers but were still
merged in the root scroll layer. This is tracked in Bug 769541.
This fixes the problem by storing the new invalid region in DisplayItemDataEntry
and clearing/setting the ThebesLayerInvalidRegion property in the
UpdateDisplayItemData callback from FrameLayerBuilder::WillEndTransaction.
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.
