(Path is actually r=froydnj.)
Bug 1400459 devirtualized nsIAtom so that it is no longer a subclass of
nsISupports. This means that nsAtom is now a better name for it than nsIAtom.
MozReview-Commit-ID: 91U22X2NydP
This ensures that if the scroll event triggers style changes, they are
reflected on the same paint.
This is accomplished by having the refresh driver fire scroll events as
an explicit step after FlushType::Style observers and rAF callbacks, and
before the actual style flush.
MozReview-Commit-ID: 4kgauD5SgVo
nsIFrame::mClass is of type enum class nsQueryFrame::ClassID which is
a strict subset of the nsQueryFrame::FrameIID values. For a concrete
frame class, its FrameIID is the same numeric value as its ClassID.
MozReview-Commit-ID: 1N0AkCGo1ol
NotifyApproximateFrameVisibilityUpdate gets the displayport so we want the base rect set before calling it.
We also don't want to record the displayport if we ignored it in the actual visibility pass.
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
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
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
