1968672 - View transition capture doesn't work if inside a nested transform.

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect)

Description

[Emilio Cobos Álvarez [:emilio]]

Attachment: Reduced test-case.

See the attached reduced test-case. Removing the transform: scale(0.99) makes the test-case work (expected rendering is pink background with "Some text" in black).

I don't see anything going terribly wrong on the layout / display list side. Nical, can you take a look at the webrender side and see if there's anything off?

Comment 1

[Nicolas Silva [:nical]]

I tried fairly hard to get a reproduction of the issue using wrench to narrow things down and ease debugging, but (invertible) transforms work nicely in this environment.

It turns out that when running this this test (in Firefox), WebRender does render the snapshot for the text element, but no subsequent display list contains the image key associated with that snapshot. I do see that we are also producing snapshots for the live capture in the following frames but there are also no image display item referring to them.
So I suspect that during DL building, we don't produce the display item for the pseudo element(s) in some situations involving transforms.

Comment 2

[Nicolas Silva [:nical]]

Unassigning myself for now since this is on the displaylist side and I have some WebRender items to look at.

Comment 3

[Emilio Cobos Álvarez [:emilio]]

This "fixes" it:

diff --git a/dom/view-transitions/ViewTransition.cpp b/dom/view-transitions/ViewTransition.cpp
index ea38f7c53caf..ec40c4f450d6 100644
--- a/dom/view-transitions/ViewTransition.cpp
+++ b/dom/view-transitions/ViewTransition.cpp

 // TODO(emilio): This might need revision.
 static CSSToCSSMatrix4x4Flagged EffectiveTransform(nsIFrame* aFrame) {
   CSSToCSSMatrix4x4Flagged matrix;
-  if (aFrame->GetSize().IsEmpty() || aFrame->Style()->IsRootElementStyle()) {
+  if (aFrame->GetSize().IsEmpty() || aFrame->Style()->IsRootElementStyle() || (true)) {
     return matrix;
   }

So interestingly it's not an ancestor transform of the captured element what causes the issue, but an ancestor transform of the element that displays it.

Comment 4

[Emilio Cobos Álvarez [:emilio]]

Display list with that change is:

    FixedPosition p=0x7f04cb7111a0 f=0x7f04cb70e120(Block(div)(-1)) key=25 bounds(0,0,76800,57330) componentAlpha(0,0,0,0) clip() asr() clipChain()  (opaque 0,0,76800,57330) (will-change=-moz-fixed-pos-containing-block) reuse-state(None) (containerASR ) (scrolltarget 3)
      nsDisplayContainer p=0x7f04cb70f6c0 f=0x7f04cb70e370(Block(div)(0)) key=20 bounds(0,0,76800,57330) componentAlpha(0,0,0,0) clip() asr() clipChain()  (opaque 0,0,76800,57330) reuse-state(None)
        BackgroundColor p=0x7f04cb710510 f=0x7f04cb70e370(Block(div)(0)) key=6 bounds(0,0,76800,57330) componentAlpha(0,0,0,0) clip() asr() clipChain() uniform  (opaque 0,0,76800,57330) hitTestInfo(0x1) hitTestArea(0,0,76800,57330) reuse-state(None) (rgba 1,0.752941,0.796079,1) backgroundRect(x=0, y=0, w=76800, h=57330)
        nsDisplayTransform p=0x7f04cb710fc8 f=0x7f04cb70e4b8(Block(div)(0)) key=67 bounds(0,0,76800,1320) componentAlpha(0,0,0,0) clip() asr() clipChain()  reuse-state(None)[ I ] prerender(full) childrenBuildingRect(x=0, y=0, w=76800, h=1440)
          CompositorHitTestInfo p=0x7f04cb7105d8 f=0x7f04cb70e4b8(Block(div)(0)) key=19 bounds(0,0,0,0) componentAlpha(0,0,0,0) clip() asr() clipChain()  hitTestInfo(0x1) hitTestArea(0,0,76800,1320) reuse-state(None)
          BlendContainer p=0x7f04cb710e98 f=0x7f04cb70e600(Block(div)(0)) key=7 bounds(0,0,76800,1320) componentAlpha(0,0,0,0) clip() asr() clipChain()  reuse-state(None)
            CompositorHitTestInfo p=0x7f04cb710678 f=0x7f04cb70e600(Block(div)(0)) key=19 bounds(0,0,0,0) componentAlpha(0,0,0,0) clip() asr() clipChain()  hitTestInfo(0x1) hitTestArea(0,0,76800,1320) reuse-state(None)
            BlendMode p=0x7f04cb710990 f=0x7f04cb70e748(ImageFrame(div)(0)) key=8 bounds(0,0,76800,1320) componentAlpha(0,0,0,0) clip() asr() clipChain()  reuse-state(None)
              Opacity p=0x7f04cb710858 f=0x7f04cb70e748(ImageFrame(div)(0)) key=37 bounds(0,0,76800,1320) componentAlpha(0,0,0,0) clip() asr() clipChain()  reuse-state(None) (opacity 1, mChildOpacityState: Unknown)
                CompositorHitTestInfo p=0x7f04cb710718 f=0x7f04cb70e748(ImageFrame(div)(0)) key=19 bounds(0,0,0,0) componentAlpha(0,0,0,0) clip() asr() clipChain()  hitTestInfo(0x1) hitTestArea(0,0,76800,1320) reuse-state(None)
                Image p=0x7f04cb7107b8 f=0x7f04cb70e748(ImageFrame(div)(0)) key=32 bounds(0,0,76800,1320) componentAlpha(0,0,0,0) clip() asr() clipChain()  reuse-state(None)
            BlendMode p=0x7f04cb710d38 f=0x7f04cb70e8d0(ImageFrame(div)(1)) key=8 bounds(0,0,76800,1320) componentAlpha(0,0,0,0) clip() asr() clipChain()  reuse-state(None)
              Opacity p=0x7f04cb710c00 f=0x7f04cb70e8d0(ImageFrame(div)(1)) key=37 bounds(0,0,76800,1320) componentAlpha(0,0,0,0) clip() asr() clipChain()  reuse-state(None) (opacity 0, mChildOpacityState: Unknown)
                CompositorHitTestInfo p=0x7f04cb710ac0 f=0x7f04cb70e8d0(ImageFrame(div)(1)) key=19 bounds(0,0,0,0) componentAlpha(0,0,0,0) clip() asr() clipChain()  hitTestInfo(0x1) hitTestArea(0,0,76800,1320) reuse-state(None)
                Image p=0x7f04cb710b60 f=0x7f04cb70e8d0(ImageFrame(div)(1)) key=32 bounds(0,0,76800,1320) componentAlpha(0,0,0,0) clip() asr() clipChain()  reuse-state(None)

If that matrix becomes anything that isn't identity, then stuff blows up.

Comment 5

[Emilio Cobos Álvarez [:emilio]]

Attachment: Bug 1968672 - Don't change z-axis for view transition transforms. r=nical,#vt

Fun one... I'll add a trivial reftest if nothing starts passing as a
result of this.

Comment 6

[Emilio Cobos Álvarez [:emilio]]

Attachment: Bug 1968672 - Fix transform basis and add a test. r=#vt

We need to compensate with the centered origin that the transform will
get.

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/42615293eb1b
https://hg.mozilla.org/integration/autoland/rev/240c8559177d
Don't change z-axis for view transition transforms. r=view-transitions-reviewers,boris

Comment 8

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/7142b07a7712
https://hg.mozilla.org/integration/autoland/rev/d34cd779b997
Fix transform basis and add a test. r=view-transitions-reviewers,nical

Comment 9

[Narcis Beleuzu [:NarcisB]]

https://hg.mozilla.org/mozilla-central/rev/240c8559177d

Comment 10

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/d34cd779b997

Comment 11

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/53099 for changes under testing/web-platform/tests

Comment 12

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Upstream PR merged by moz-wptsync-bot