If we disable APZ on an individual scrollable element by setting the "disable APZ"
flag on the ScrollMetadata, we should also disable paint-skipping for that element.
If we don't do this, we end up in a situation where the APZ code is not applying
the async transform but is sending repaint requests expecting the main thread to
do repaints. Meanwhile the main-thread thinks that it can send empty transactions
and have APZ update the async transform (a.k.a. paint-skipping). So visually
neither APZ nor main-thread have an effect and the element doesn't appear to
scroll except with the tile-aligned displayport shifts. Disabling paint-skipping
on the element fixes the issue.
MozReview-Commit-ID: H4wpVLw8r8X
The scroll frame is almost always the content's primary frame and if so
it already has the correct style values and the nsFrame ctor has set
mWritingMode correctly based on those. For the edge cases where it's
not the primary frame, e.g. <fieldset style=overflow:scroll>, the UA
sheet specifies 'inherit' for the relevant properties so it has
the correct style values in this case too.
MozReview-Commit-ID: 1FMFNfF0IqU
This patch is written by the following script with some manual adjustment to
the comment in nsRubyTextContainerFrame.cpp and nsRubyFrame.cpp, and
nsColumnSetFrame's constructor.
function rename() {
find layout\
-type f\
\( -name "*.cpp" -or\
-name "*.h" \)\
-exec sed -i -r "s/$1/$2/g" "{}" \;
}
rename "nsReflowStatus *([a-zA-Z0-9]*) = NS_FRAME_COMPLETE" "nsReflowStatus \1"
rename "([a-zA-Z0-9.*]*) *= NS_FRAME_COMPLETE;" "\1.Reset();"
rename "([a-zA-Z0-9.*]*) == NS_FRAME_COMPLETE" "\1.IsEmpty()"
MozReview-Commit-ID: 9tqQAHvdQex
This is the bulk of the changes.
- DisplayItemScrollClip is removed. Instead, we will have 1) ActiveScrolledRoot
and 2) DisplayItemClipChain.
- ActiveScrolledRoot points to a scroll frame and allows traversing up the
scroll frame chain.
- DisplayItemClipChain is a linked list of clips, each clip being associated
with the ActiveScrolledRoot that moves this clip.
- Each display item has an ActiveScrolledRoot and a clip chain.
- nsDisplayItem::GetClip returns the item of the clip chain that scrolls with
the item's ASR. The separation between "regular clip" and "scroll clips"
mostly goes away.
- Tracking clips in the display list builder's clip state happens very
similarly to how regular clips used to be tracked - there's a clip chain for
content descendants and a clip chain for containing block descendants. These
clip chains are intersected to create the combined clip chain.
- There are strict rules for the ASR of a container item: A container item's
ASR should be the innermost ASR which the item has finite clipped bounds with
respect to.
- At some point in the future, ASRs and AGRs should be reunified, but I haven't
done that yet, because I needed to limit the scope of the change.
MozReview-Commit-ID: KYEpWY7qgf2
If, within a single refresh driver tick, the scroll position is updated by JS
explicitly, and then subsequently also updated by a frame reconstruction, the
scroll origin from the former (nsGkAtoms::other) can get clobbered by the latter
(to nsGkAtoms::restore). The restore scroll origin is "weaker" in that it can
be ignored by the APZ code in some circumstances. This is undesirable because
it means the JS scroll update also gets ignored. This patch ensures that when
setting the scroll origin we don't do this clobbering of stronger origins with
weaker origins.
MozReview-Commit-ID: DA4EHp1Debu
Previously we weren't sending scroll position updates with origin nsGkAtoms::restore
over to the APZ at all, on the assumption that they should never clobber an APZ
scroll offset. However, there are scenarios where that is not true.
In particular, during a frame reconstruction, a layers update may be sent to the
compositor between the time a scrollframe has RestoreState() called on it, and
the time the scrollframe has ScrollToRestoredPosition() called on it. The layers
update that happens during this interval (correctly) sends a scroll position of
(0,0), and forces the APZ to scroll to that position. This is necessary to
prevent APZ from remaining at an invalid scroll offset while the frame is still
being rebuilt.
However, once ScrollToRestoredPosition() is called and the old scroll offset is
restored, that restored scroll position needs to get sent to the APZ in order to
have it properly restore to the original scroll position. In order to do this,
the main thread must flag the metrics with a scroll offset update. Since the user
may have scrolled concurrently in the compositor from the (0,0) position, we also
need to check for that case in the APZ code and avoid restoring the scroll
position. This is equivalent to the corresponding main-thread code in
ScrollToRestoredPosition().
MozReview-Commit-ID: LxRapVSrsJ3
We want the maximum scroll position to be aligned with layer pixels. That way
we don't have to re-rasterize the scrolled contents once scrolling hits the
edge of the scrollable area.
Here's how we determine the maximum scroll position: We get the scroll port
rect, snapped to layer pixels. Then we get the scrolled rect and also snap
that to layer pixels. The maximum scroll position is set to the difference
between right/bottom edges of these rectangles.
Now the scrollable area is computed by adding this maximum scroll position
to the unsnapped scroll port size.
The underlying idea here is: Pretend we have overflow:visible so that the
scrolled contents start at (0, 0) relative to the scroll port and spill over
the scroll port edges. When these contents are rendered, their rendering is
snapped to layer pixels. We want those exact pixels to be accessible by
scrolling.
This way of computing the snapped scrollable area ensures that, if you scroll
to the maximum scroll position, the right/bottom edges of the rendered
scrolled contents line up exactly with the right/bottom edges of the scroll
port. The scrolled contents are neither cut off nor are they moved too far.
(This is something that no other browser engine gets completely right, see the
testcase in bug 1012752.)
There are also a few disadvantages to this solution. We snap to layer pixels,
and the size of a layer pixel can depend on the zoom level, the document
resolution, the current screen's scale factor, and CSS transforms. The snap
origin is the position of the reference frame. So a change to any of these
things can influence the scrollable area and the maximum scroll position.
This patch does not make us adjust the current scroll position in the event
that the maximum scroll position changes such that the current scroll position
would be out of range, unless there's a reflow of the scrolled contents. This
means that we can sometimes render a slightly inconsistent state where the
current scroll position exceeds the maximum scroll position. We can fix this
once it turns out to be a problem; I doubt that it will be a problem because
none of the other browsers seems to prevent this problem either.
The size of the scrollable area is exposed through the DOM properties
scrollWidth and scrollHeight. At the moment, these are integer properties, so
their value is rounded to the nearest CSS pixel. Before this patch, the
returned value would always be within 0.5 CSS pixels of the value that layout
computed for the content's scrollable overflow based on the CSS styles of the
contents.
Now that scrollWidth and scrollHeight also depend on pixel snapping, their
values can deviate by up to one layer pixel from what the page might expect
based on the styles of the contents. This change requires a few changes to
existing tests.
The fact that scrollWidth and scrollHeight can change based on the position of
the scrollable element and the zoom level / resolution may surprise some web
pages. However, this also seems to happen in Edge. Edge seems to always round
scrollWidth and scrollHeight upwards, possibly to their equivalent of layout
device pixels.
MozReview-Commit-ID: 3LFV7Lio4tG
