[view-transitions] Mispositioned snapshots on https://codepen.io/bramus/full/mdowgYX

[mattwoodrow]

159906e

[view-transitions] Mispositioned snapshots on https://codepen.io/bramus/full/mdowgYX
https://bugs.webkit.org/show_bug.cgi?id=272185
rdar://125931829

Reviewed by Simon Fraser.

We were previously unconditionally substracting the scroll position from the transform when positioning the snapshots.
This is incorrect in some cases, like when the element is fixed positioned.

This makes use of the existing TransformState/mapLocalToContainer code to correctly account for position:fixed when accumulating
transforms through ancestors.

It also adds support for flattening the 'tracked' transform when crossing 3d rendering context boundaries, by setting the 3rd row
and column of the TransformationMatrix to 0.

* LayoutTests/imported/w3c/web-platform-tests/css/css-view-transitions/new-content-flat-transform-ancestor-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-view-transitions/new-content-flat-transform-ancestor-ref.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-view-transitions/new-content-flat-transform-ancestor.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-view-transitions/new-content-preserve-3d-ancestor-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-view-transitions/new-content-preserve-3d-ancestor-ref.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-view-transitions/new-content-preserve-3d-ancestor.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-view-transitions/new-content-transform-position-fixed-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-view-transitions/new-content-transform-position-fixed-ref.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-view-transitions/new-content-transform-position-fixed.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-view-transitions/root-scrollbar-with-fixed-background-expected.html:
* LayoutTests/imported/w3c/web-platform-tests/css/css-view-transitions/root-scrollbar-with-fixed-background-ref.html:
* LayoutTests/imported/w3c/web-platform-tests/css/css-view-transitions/root-scrollbar-with-fixed-background.html:
* Source/WebCore/dom/ViewTransition.cpp:
(WebCore::ViewTransition::copyElementBaseProperties):
* Source/WebCore/platform/graphics/transforms/TransformState.cpp:
(WebCore::TransformState::translateMappedCoordinates):
(WebCore::TransformState::flattenWithTransform):
* Source/WebCore/platform/graphics/transforms/TransformState.h:
* Source/WebCore/platform/graphics/transforms/TransformationMatrix.cpp:
(WebCore::TransformationMatrix::flatten):
* Source/WebCore/platform/graphics/transforms/TransformationMatrix.h:
* Source/WebCore/rendering/RenderObject.cpp:
(WebCore::RenderObject::localToAbsoluteTransform const):
* Source/WebCore/rendering/RenderObject.h:

Canonical link: https://commits.webkit.org/279186@main

13f3033

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	🧪 wpe-wk2	✅ 🧪 wincairo-tests
✅ 🧪 webkitperl	🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🛠 wpe-cairo
	🧪 api-ios	✅ 🧪 mac-wk2	✅ 🛠 gtk
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2	🧪 gtk-wk2
	🛠 tv-sim	✅ 🧪 mac-wk2-stress	🧪 api-gtk
🛠 🧪 merge	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on previous version of this PR (hash 0a8c299)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	🛠 ios	✅ 🛠 mac	🛠 wpe	🛠 wincairo
🧪 bindings	🛠 ios-sim	✅ 🛠 mac-AS-debug	🧪 wpe-wk2	🧪 wincairo-tests
✅ 🧪 webkitperl	🧪 ios-wk2	🧪 api-mac	🧪 api-wpe
	🧪 ios-wk2-wpt	🧪 mac-wk1	🛠 wpe-cairo
	🧪 api-ios	🧪 mac-wk2	🛠 gtk
	🛠 tv	⏳ 🧪 mac-AS-debug-wk2	🧪 gtk-wk2
	🛠 tv-sim	🧪 mac-wk2-stress	🧪 api-gtk
	🛠 watch
	🛠 watch-sim

[webkit-early-warning-system]

EWS run on previous version of this PR (hash 33d9153)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	✅ 🧪 wincairo-tests
✅ 🧪 webkitperl	❌ 🧪 ios-wk2	⏳ 🧪 api-mac	✅ 🧪 api-wpe
	❌ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🛠 wpe-cairo
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🛠 gtk
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2	❌ 🧪 gtk-wk2
	✅ 🛠 tv-sim	✅ 🧪 mac-wk2-stress	✅ 🧪 api-gtk
	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on previous version of this PR (hash 85d5853)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	✅ 🧪 wincairo-tests
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🛠 wpe-cairo
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🛠 gtk
	✅ 🛠 tv	❌ 🧪 mac-AS-debug-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 tv-sim	✅ 🧪 mac-wk2-stress	✅ 🧪 api-gtk
	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on previous version of this PR (hash dd507bc)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	❌ 🛠 ios	❌ 🛠 mac	❌ 🛠 wpe	🛠 wincairo
✅ 🧪 bindings	❌ 🛠 ios-sim	❌ 🛠 mac-AS-debug	❌ 🧪 wpe-wk2	🧪 wincairo-tests
✅ 🧪 webkitperl	❌ 🧪 ios-wk2	❌ 🧪 api-mac	❌ 🧪 api-wpe
	❌ 🧪 ios-wk2-wpt	❌ 🧪 mac-wk1	❌ 🛠 wpe-cairo
	❌ 🧪 api-ios	❌ 🧪 mac-wk2	❌ 🛠 gtk
	❌ 🛠 tv	❌ 🧪 mac-AS-debug-wk2	❌ 🧪 gtk-wk2
	🛠 tv-sim	❌ 🧪 mac-wk2-stress	❌ 🧪 api-gtk
	🛠 watch
	❌ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on current version of this PR (hash 13f3033)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	🧪 wpe-wk2	✅ 🧪 wincairo-tests
✅ 🧪 webkitperl	🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🛠 wpe-cairo
	🧪 api-ios	✅ 🧪 mac-wk2	✅ 🛠 gtk
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2	🧪 gtk-wk2
	🛠 tv-sim	✅ 🧪 mac-wk2-stress	🧪 api-gtk
🛠 🧪 merge	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-commit-queue]

Committed 279186@main (159906e): https://commits.webkit.org/279186@main

Reviewed commits have been landed. Closing PR #28808 and removing active labels.