[web] Anchor platform view slots to top-left to fix RTL document layout - #194601

flutter/flutter@5e805bf...ee8b482

2026-10-31 [email protected] Roll Skia from 9bab765df357 to 607de4b035dc (1 revision) (flutter/flutter#195728)
2026-10-31 [email protected] Roll Skia from 284054bec98a to 9bab765df357 (2 revisions) (flutter/flutter#195726)
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2026-10-30 [email protected] Fix XcodeProjectInterpreter dependency cycle in flutter_tools (flutter/flutter#195694)
2026-10-30 [email protected] Document that Positioned also works inside an Overlay (flutter/flutter#190607)
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2026-10-30 [email protected] Adds Vulkan sync validation test run (flutter/flutter#195596)
2026-10-30 [email protected] [Android] Let the raster thread use every core of a chip without little cores (flutter/flutter#195071)
2026-10-30 [email protected] Roll Skia from 121d04c01e2d to ce0b85b46db6 (6 revisions) (flutter/flutter#195699)
2026-10-30 [email protected] [web] Anchor platform view slots to top-left to fix RTL document layout (flutter/flutter#194601)
2026-10-30 [email protected] Update golden file testing docs (flutter/flutter#195449)
2026-10-30 [email protected] [tool] Migrate Cache.flutterRoot static state to instance configuration (flutter/flutter#190795)
2026-10-30 [email protected] Apply view metrics overrides below the framework (flutter/flutter#194311)
2026-10-30 [email protected] Roll Skia from c0c46ee9f938 to 121d04c01e2d (9 revisions) (flutter/flutter#195687)
2026-10-30 [email protected] Use uniforms in the Porter Duff blend shader instead of specialization constants (flutter/flutter#195458)
2026-10-30 [email protected] [flutter_tools] Inject dependencies into iOS, macOS, and Windows application packages (flutter/flutter#194047)

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…ut (flutter#194601)

Platform view slots use `position: absolute` with CSS transforms to
position elements. When the host document uses `dir="rtl"`, the browser
defaults the static position of unconstrained absolute elements to the
right edge instead of the left, pushing the slot offscreen when the 2D
translation matrix is applied.
This explicitly sets `top: 0` and `left: 0` in `_resetAnchor` to ensure
the transform origin and base coordinates always
start at (0, 0).

## Description

When Flutter Web is embedded in a webpage where `<html dir="rtl">` or
`<body dir="rtl">` is set, platform views (`HtmlElementView`) render
offscreen to the right.
Fixes flutter#195150

### Cause
`<flt-platform-view-slot>` uses `position: absolute` without explicit
`top`/`left` anchors. Per CSS 2.1 §10.3.7, an unconstrained absolutely
positioned element's static horizontal position aligns to the containing
block's right edge in an RTL context. When Flutter translates the
element with `transform: matrix(1, 0, 0, 1, x, y)`, the `+x` translation
offsets from the right edge rather than (0, 0) top-left, throwing the
view offscreen.

### Fix
Explicitly set `top: 0` and `left: 0` in `_resetAnchor`
(`embedder.dart`) for platform view slots so coordinate transforms
always calculate from (0, 0).


## Tests Added

- `test/ui/platform_view_position_test.dart`: Added `Platform view slot
coordinates are anchored to top-left even in RTL document` validating
slot position and rect when `domDocument.documentElement.dir == 'rtl'`.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [AI contribution guidelines] and understand my
responsibilities, or I am not using AI tools.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant in-code documentation (doc comments with
`///`).
- [ ] If this PR introduces a new feature or capability, I created and
linked a website documentation issue or PR in [flutter/website] (or
verified none is needed).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

---------

Co-authored-by: Mouad Debbar <[email protected]>
Co-authored-by: Mouad Debbar <[email protected]>
Co-authored-by: zhongliugo <[email protected]>