It's not obvious that it does this (unless you read the comment or the code), and we don't gain much by doing it.
Also we need to split it up for the next patch in this bug.
Without this patch, patch 2 will cause assertions since
nsFrame::DestroyFrom calls nsFrame::HasCSSAnimations (at a time when the
child frame has been destroyed), which calls into the code modified in
patch 2 to call GetStyleFrame.
Temporarily rename GetDisplayPort to GetDisplayPortRelativeToScrollPort for the duration of this patchset.
This means that every caller of GetDisplayPort is guaranteed to be touched by this patchset (assuming it compiles), and thus each call site can be checked in review to make sure it is relative to the correct coordinate system.
This makes the one caller that needs the displayport rect have to ask for it seperately.
The reason for this is later in the patch series we need to add "RelativeToScrollFrame/Port" to all displayport getters, but there is no semantically good way to do that to the name GetOrMaybeCreateDisplayPort.
This makes the one caller that needs the displayport rect have to ask for it seperately.
The reason for this is later in the patch series we need to add "RelativeToScrollFrame/Port" to all displayport getters, but there is no semantically good way to do that to the name ViewportHasDisplayPort.
AutoTextRun now only needs a DrawTarget instead of an nsRenderingContext, and
similar nsRenderingContext/gfxContext-to-DrawTarget replacements can be
propagated a long way up the call graph. This patch replaces 93 occurrences of
nsRenderingContext and 135 occurrences of gfxContext with DrawTarget; that's
13% of them.
The patch is mostly plumbing changes. A couple of not-entirely-plumbing
changes:
- It adds a comment about the null check in
gfxGlyphExtents::GetTightGlyphExtentsAppUnits().
- A couple of functions simply had an unused gfxContext or nsRenderingContext
parameter removed, e.g. SetLineBreaks().
The two flags combined used to be represented by just RENDER_IGNORE_VIEWPORT_SCROLLING. Until http://hg.mozilla.org/mozilla-central/rev/99279c1c33cc (bug 590294) split RENDER_DOCUMENT_RELATIVE out. It split out the requested rect to be document relative. But it also split out the part about "drawing the document as if it had not been scrolled" with the new flag, but the comments for that part didn't get updated.
The names of the flags are perhaps inaccurate, but changing that requires changing a lot more code.
We may want to do this for fixed pos frames in all documents (not just root documents). However, this patch only maintains the previous behaviour on purpose.
Instead of returning the root scroll frame if we encountered the root frame (which is the parent of the root scroll frame).
This allows the use of GetNearestScrollableFrame to walk up the frame tree without getting into a infinite loop going from root scroll frame to root frame and back.
This regresses bug 1105823 in that fixed pos frames will no longer find the root scroll frame of their document. The next patch will fix that.
The only other type of frame that will be affected when calling GetNearestScrollableFrame are viewport (root) frames. However, the only user of SCROLLABLE_ALWAYS_MATCH_ROOT (APZCCallbackHelper) calls GetNearestScrollableFrame on the result of a hit test on a display list. Viewport frames never create any display items whose HitTest function could return the viewport frame.
Removing the "stop at ancestor" parameter from functions that compute AGR meant that nsLayoutUtils::GetAnimatedGeometryRootFor could no longer pass the display item's reference frame as the "stop at ancestor" which meant that the AGR could cross the reference frame for the item, which we don't want. So we make transformed frames into AGRs.
This makes the computation of display items whose frames are transformed tricky. We need the AGR of the transform item to be the ancestor AGR, not the underlying frame of the transform item (which is now an AGR). So we modify nsLayoutUtils::GetAnimatedGeometryRootFor to handle this. (The patch from bug 1205087 didn't suffer from this problem because it special cased the computation of the AGR of transform items. Leaving anybody who called nsLayoutUtils::GetAnimatedGeometryRootFor to get the wrong result.)
The computation of the AGR for scroll metadata in ContainerState::ProcessDisplayItems specifically bypassed nsLayoutUtils::GetAnimatedGeometryRootFor to avoid it's special processing of fixed background items. However we do want the AGR for scroll metadata to do this special processing of transform items. So we add a flag to bypass the fixed background behaviour and use it for the scroll metadata AGR.
This removes the "aStopAtAncestor" argument to agr computing functions. In most cases an AGR was passed for the stop at ancestor, so we'd stop at it anyway since it was an AGR. Most of the remaining cases the root reference frame was passed. And in a few cases something else was passed, which we probably don't want (returning something that isn't an AGR and isn't the root reference frame as an AGR).
The ShouldFixToViewport case is a little tricky. We want to get the AGR of the nearest viewport frame, but only if we don't have to cross our root reference frame to get it. This happens in practice for example when a select dropdown has background-attachment: fixed inside it.
Except for the ShouldFixToViewport bit, this patch is a subset of part 3 in bug 1205087 (which has more changes, and has been temporarily backed out, the remaining bits can hopefully land soon).
The ShouldFixToViewport part is by Timothy Nikkel <tnikkel@gmail.com>
