[web_paragraph] Honor TextHeightBehavior.leadingDistribution and default to proportional by Rusino · Pull Request #193736 · flutter/flutter

Rusino · 2026-10-02T21:33:11Z

Part of #193731. Split out of #193403 (third of four independent PRs; the others are #193733 and #193734, and #193403 is stacked on top of this PR).

Problem

TextHeightBehavior.leadingDistribution was ignored. WebParagraphStyle never passed textHeightBehavior.leadingDistribution to the root WebTextStyle, and RootStyleNode._leadingDistribution always returned null, so the value could not reach LineBlock. Only an explicit TextStyle(leadingDistribution: …) had any effect.
The default leading distribution was even. LineBlock treated null the same as TextLeadingDistribution.even (half-leading). SkParagraph (and therefore the native engine and CanvasKit) default to proportional: TextStyle::fHalfLeading is false unless leadingDistribution == even is set, and dart:ui's TextHeightBehavior.leadingDistribution defaults to TextLeadingDistribution.proportional.
Negative half-leading clamped fontBoundingBoxDescent to 0.0. TextLine initialized fontBoundingBoxAscent and fontBoundingBoxDescent to 0.0 and accumulated every block with math.max(0.0, ...). With TextLeadingDistribution.even and a small height multiplier (where height * fontSize < rawAscent + rawDescent), extraLeading / 2 is negative and multipliedFontBoundingBoxDescent can become negative; math.max(0.0, ...) clamped it to 0.0, inflating the line height above height * fontSize.

Fix

WebParagraphStyle propagates textHeightBehavior?.leadingDistribution into the root WebTextStyle; RootStyleNode._leadingDistribution returns style.leadingDistribution. Child TextStyles still override it through ChildStyleNode as before.
LineBlock: null now falls through to the proportional branch (ascent and descent are scaled by height * fontSize / (ascent + descent)), even keeps the half-leading behavior.
TextLine.updateBoundingBox: track _hasLineMetrics so the first block on the line initializes fontBoundingBoxAscent and fontBoundingBoxDescent directly (preserving a negative descent), while subsequent blocks take math.max.

Behavior change

For any paragraph with a height multiplier and no explicit leadingDistribution, the line height is unchanged but the baseline moves: the extra leading is now split in proportion to the font's ascent/descent instead of 50/50. This brings WebParagraph in line with CanvasKit/Skwasm output for the same ParagraphStyle; WebParagraph is not the default renderer yet, so no app-facing change on stable.

Tests

New paragraph_line_height_test.dart:
- Height multiplier scales ascent and descent proportionally by default — checks the scaled line keeps height * fontSize, that ascent/descent scale by the same factor by default, that TextHeightBehavior(leadingDistribution: even) adds equal leading on both sides, and that the two differ. Fails on master (default was even and the THB value was ignored).
- Half-leading with a small height multiplier preserves negative descent — checks that height: 0.1 with TextLeadingDistribution.even keeps a negative descent and total height 0.1 * fontSize.
Existing webparagraph/* and ui/paragraph_builder_test.dart suites pass.
WebParagraph corpus (preferWebParagraph + forceTestFonts vs origin/master b7315d76579e): 0 fixed standalone, +2 new tests passing, 0 regressions (base of the [web_paragraph] Honor TextHeightBehavior.leadingDistribution and default to proportional #193736 -> [web_paragraph] Honor TextHeightBehavior.applyHeightToFirstAscent and applyHeightToLastDescent #193773 -> [web_paragraph] Apply StrutStyle to line metrics and placeholders #193774 -> [web_paragraph] Compute empty paragraph line metrics with height, TextHeightBehavior, and StrutStyle #193403 stack that fixes 34 corpus tests; framework TextPainter line-height tests in test/painting/text_painter_test.dart also call getBoxesForSelection with BoxHeightStyle.tight and are unlocked when combined with [web_paragraph] Fix placeholder positioning and BoxHeightStyle.tight boxes #193734).

Pre-launch Checklist

…ult to proportional

flutter-dashboard · 2026-10-09T19:27:26Z

This pull request is not mergeable in its current state, likely because of a merge conflict. Pre-submit CI jobs were not triggered. Pushing a new commit to this branch that resolves the issue will result in pre-submit jobs being scheduled.

gemini-code-assist

Code Review

This pull request updates the web paragraph layout engine to propagate the default leadingDistribution from ParagraphStyle to the root text style, and correctly handles proportional and even leading distributions during line layout. It also ensures line metrics are initialized properly using a new _hasLineMetrics flag, and adds comprehensive unit tests for these behaviors. The review feedback suggests formatting two inline comments in layout.dart as complete sentences ending with a period to comply with the style guide.

…flutter#193733) Part of flutter#193731. Split out of flutter#193403 (first of four independent PRs; the others are flutter#193734 and flutter#193736, and flutter#193403 itself will be rebased on top once these land). ### Problem - `ChildStyleNode._height` converted `style.height == ui.kTextHeightNone` to `null` *before* falling back to `parent._height`, so a child `TextStyle(height: ui.kTextHeightNone)` could never override a non-null parent height (`ParagraphStyle(height: 3.0)` + `pushStyle(TextStyle(height: kTextHeightNone))` still laid out the line at 3x). - `LineBlock` only checked `span.style.height == null`, so `ParagraphStyle(height: ui.kTextHeightNone)` (`0.0`) multiplied the line ascent/descent by `0.0` instead of disabling the height multiplier. ### Fix - `ChildStyleNode._height` keeps `style.height` as-is: `style.height ?? parent._height`. `kTextHeightNone` now reaches `LineBlock`, which is the one place that interprets it. - `LineBlock`: `height == null || height == ui.kTextHeightNone` → raw font ascent/descent, no scaling (same as the native path, where `paragraph_builder.cc` sets `has_height_override = style.height != kTextHeightNone`). - `LineBlock` uses `StyleManager.defaultFontSize` instead of a hardcoded `14.0`. - `WebStrutStyle` already normalizes `kTextHeightNone` to `null` in its constructor, so struts need no change. ### Tests - `paragraph_get_boxes_test.dart`: `layout with kTextHeightNone disables parent height multiplier`, `layout with ParagraphStyle(kTextHeightNone)`. - **WebParagraph corpus (`preferWebParagraph` + `forceTestFonts` vs `origin/master` `b7315d76579e`)**: 20,012 tests (18,765 executed, 1,247 skipped) — **503 -> 503 failures (0 fixed standalone, +2 new tests passing, 0 regressions)**. - *Note:* Existing corpus tests for `kTextHeightNone` also depend on other issues (`test/ui/paragraph_builder_test.dart: kTextHeightNone StrutStyle` is unlocked in flutter#193774 once `StrutStyle` is applied; `test/painting/text_painter_test.dart: kTextHeightNone unsets the text height multiplier` still fails due to Chromium's integer-rounded `FlutterTest` font metrics at `10px` where `ascent + descent = 11 != 10`). ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [ ] 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 `///`). - [x] 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.  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flutter-dashboard · 2026-10-12T19:43:05Z

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Changes reported for pull request #193736 at sha 04ad498

Test that a child TextStyle's leadingDistribution takes precedence over the paragraph's TextHeightBehavior.leadingDistribution. Assisted-by: Gemini 3.8 Flash (High)

flutter/flutter@426be96...5c7e45a 2026-10-15 [email protected] [web_paragraph] Honor TextHeightBehavior.leadingDistribution and default to proportional (flutter/flutter#193736) 2026-10-15 [email protected] Roll Skia from 79a00d7c4898 to d131b7789482 (2 revisions) (flutter/flutter#194446) 2026-10-15 [email protected] Roll Dart SDK from b8ffa9233096 to 84686ea04815 (1 revision) (flutter/flutter#194442) 2026-10-15 [email protected] Roll Dart SDK from e81af2dac9d1 to b8ffa9233096 (1 revision) (flutter/flutter#194432) 2026-10-15 [email protected] Roll Skia from ef24b8f87a2a to 79a00d7c4898 (4 revisions) (flutter/flutter#194431) 2026-10-15 [email protected] Roll Skia from 48c51004ee4e to ef24b8f87a2a (1 revision) (flutter/flutter#194427) 2026-10-15 [email protected] Roll Dart SDK from 6b50116630d0 to e81af2dac9d1 (5 revisions) (flutter/flutter#194422) 2026-10-15 [email protected] Roll Skia from b1be97266d3a to 48c51004ee4e (10 revisions) (flutter/flutter#194421) 2026-10-15 [email protected] RawAutocomplete: Fix focusNode listener mismatch in didUpdateWidget/dispose (flutter/flutter#190686) 2026-10-14 [email protected] [flutter_tools] Wait for iOS simulator log stream before launch (flutter/flutter#193142) 2026-10-14 [email protected] Move Material/Cupertino PRs from design triage to framework triage (flutter/flutter#194244) 2026-10-14 [email protected] refactor(flutter_tools): share FlutterCommand options and OptionBundles (flutter/flutter#194356) 2026-10-14 [email protected] Roll pub packages (flutter/flutter#194413) 2026-10-14 [email protected] Add ContextMenuButtonKind (flutter/flutter#193528) 2026-10-14 [email protected] Split SwiftPM plugin into multiple products (flutter/flutter#193521) 2026-10-14 [email protected] Roll Skia from 43d707a3be0e to b1be97266d3a (8 revisions) (flutter/flutter#194392) 2026-10-14 [email protected] Roll pub packages (flutter/flutter#194398) 2026-10-14 [email protected] [flutter_tools] Migrate AndroidSdk and AndroidStudio away from globals (flutter/flutter#193650) 2026-10-14 [email protected] [flutter_tools] Reload widget-preview when data assets change (flutter/flutter#193437) 2026-10-14 [email protected] [flutter tool] suppress sub-tool analytics during first run (flutter/flutter#194320) 2026-10-14 [email protected] Roll Skia from acde3755d2e2 to 43d707a3be0e (1 revision) (flutter/flutter#194385) If this roll has caused a breakage, revert this CL and set the roller to dry run mode using the controls here: https://autoroll.skia.org/r/flutter-packages Please CC [email protected],[email protected] on the revert to ensure that a human is aware of the problem. To file a bug in Packages: https://github.com/flutter/flutter/issues/new/choose To report a problem with the AutoRoller itself, please file a bug: https://issues.skia.org/issues/new?component=1389291&template=1850622 Documentation for the AutoRoller is here: https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

…boxes (flutter#193734) Part of flutter#193731. Split out of flutter#193403 (second of four independent PRs; the others are flutter#193733 and flutter#193736, and flutter#193403 itself will be rebased on top once these land). ### Problem - **Placeholder vertical position was computed too early.** `PlaceholderBlock.calculatePlaceholderTop` set `block.advance` from the line ascent *as it was at that moment* before folding `block.ascent` into the line. A placeholder taller than the preceding text (or a later, taller placeholder on the same line) grew `line.fontBoundingBoxAscent` afterwards in `line.updateBoundingBox(block)`, leaving placeholder `advance.top` positioned against a stale ascent. `getBoxesForPlaceholders` returned those stale rects, so a placeholder box could sit above the line's top (negative `top`) and disagree with `getBoxesForRange` for the same range. - **`BoxHeightStyle.tight` returned the height-scaled box for text.** `getBoxesForRange` used `multipliedFontBoundingBoxAscent` / `multipliedHeight`, i.e. the box included the extra leading added by `TextStyle.height`. SkParagraph's `TextLine::getRectsForRange` returns the unscaled glyph bounds for `tight` (`Rect::MakeXYWH(..., -run.ascent(), ..., run.descent())` relative to the baseline). The same code path was also applied to `PlaceholderBlock`, whose `advance` is already line-relative, producing a double-shifted box. ### Fix - `PlaceholderBlock` & `addLine`: split placeholder layout into two passes: - Pass 1 calls `block.calculatePlaceholderMetrics(line.fontBoundingBoxAscent, line.fontBoundingBoxDescent)` to compute each placeholder's `ascent`/`descent` and folds them into the line metrics via `line.updateBoundingBox(block)`. - Pass 2, after `line.fontBoundingBoxAscent` is final, calls `block.calculatePlaceholderTop(line.fontBoundingBoxAscent)` to compute `top = lineAscent - ascent` and set `block.advance = Rect.fromLTWH(spanShiftFromLineStart, top, span.width, span.height)`. - `getBoxesForRange`, `BoxHeightStyle.tight`: - `TextBlock`: `top = line.advance.top + line.fontBoundingBoxAscent - block.rawFontBoundingBoxAscent`, `height = rawFontBoundingBoxAscent + rawFontBoundingBoxDescent` (unscaled glyph bounds positioned at the baseline, matching SkParagraph). - `PlaceholderBlock`: `top = firstRect.top + line.advance.top`, `height = span.height` — `block.advance` is already relative to the line, so no extra ascent shift. - Removed the unused vertical `.translate(...)` on `firstRect` for `TextBlock`, since `firstRect` only provides `left` and `width` while `top` and `bottom` are computed per `BoxHeightStyle`. ### Tests - `paragraph_get_boxes_test.dart`: - `getBoxesForRange and getBoxesForPlaceholders return matching boxes for placeholders` — two placeholders on one line where the second is taller; checks both APIs agree, `top >= 0`, and the box sizes equal the placeholder sizes. On `master`: `getBoxesForPlaceholders` returns `(0, -12, 50, 18)` for the first placeholder while `getBoxesForRange(0, 1)` returns `(0, 14, 50, 44)`. - `BoxHeightStyle.tight uses unscaled glyph height and respects TextHeightBehavior` — `height: 3.0` with `even` leading; `tight` box height equals the unscaled line height and is centered in the 60px line. On `master` the `tight` box is 60px tall instead of 22px. - Existing `paragraph_get_boxes_test.dart` and `paragraph_placeholders_test.dart` pass. - **Full WebParagraph corpus (`--full`, `preferWebParagraph` + `forceTestFonts` vs `origin/master` `b7315d76579e`)**: - Part 1 (`web_ui`): `16/16` `webparagraph/*` (`+198 ~5 -1`, **+2** new tests passing) + `60/60` `test/ui/*` (`+1354 ~5 -41`). - Part 2 (`packages/flutter`, `894/894` suites across `8/8` shards): `+16712 ~1237 -459` vs baseline `+16710 ~1237 -461` (**+3** existing tests fixed; **1** apparent golden diff in `test/cupertino/text_field_test.dart: Overflow clipBehavior none golden` where on `origin/master` two bugs cancelled out — missing `StrutStyle(forceStrutHeight: true)` from flutter#193774 inflated the line ascent by 83px while the old single-pass `calculatePlaceholderTop` shifted the placeholder by `-83px` detached from its `'Hi'` text; resolved once flutter#193774 lands). - Jointly with flutter#193736 + flutter#193773 also unlocks `test/painting/text_painter_test.dart: TextPainter line-height half-leading with leading trim`. <details> <summary>Fixed corpus tests vs <code>origin/master</code> (3)</summary> - `packages/flutter` :: `test/painting/text_painter_test.dart: TextPainter line-height TextLeadingDistribution falls back to paragraph style` - `packages/flutter` :: `test/painting/text_painter_test.dart: TextPainter line-height half-leading` - `packages/flutter` :: `test/painting/text_painter_test.dart: TextPainter widget span` </details> ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [ ] 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 `///`). - [x] 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.  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…flutter#193733) Part of flutter#193731. Split out of flutter#193403 (first of four independent PRs; the others are flutter#193734 and flutter#193736, and flutter#193403 itself will be rebased on top once these land). ### Problem - `ChildStyleNode._height` converted `style.height == ui.kTextHeightNone` to `null` *before* falling back to `parent._height`, so a child `TextStyle(height: ui.kTextHeightNone)` could never override a non-null parent height (`ParagraphStyle(height: 3.0)` + `pushStyle(TextStyle(height: kTextHeightNone))` still laid out the line at 3x). - `LineBlock` only checked `span.style.height == null`, so `ParagraphStyle(height: ui.kTextHeightNone)` (`0.0`) multiplied the line ascent/descent by `0.0` instead of disabling the height multiplier. ### Fix - `ChildStyleNode._height` keeps `style.height` as-is: `style.height ?? parent._height`. `kTextHeightNone` now reaches `LineBlock`, which is the one place that interprets it. - `LineBlock`: `height == null || height == ui.kTextHeightNone` → raw font ascent/descent, no scaling (same as the native path, where `paragraph_builder.cc` sets `has_height_override = style.height != kTextHeightNone`). - `LineBlock` uses `StyleManager.defaultFontSize` instead of a hardcoded `14.0`. - `WebStrutStyle` already normalizes `kTextHeightNone` to `null` in its constructor, so struts need no change. ### Tests - `paragraph_get_boxes_test.dart`: `layout with kTextHeightNone disables parent height multiplier`, `layout with ParagraphStyle(kTextHeightNone)`. - **WebParagraph corpus (`preferWebParagraph` + `forceTestFonts` vs `origin/master` `b7315d76579e`)**: 20,012 tests (18,765 executed, 1,247 skipped) — **503 -> 503 failures (0 fixed standalone, +2 new tests passing, 0 regressions)**. - *Note:* Existing corpus tests for `kTextHeightNone` also depend on other issues (`test/ui/paragraph_builder_test.dart: kTextHeightNone StrutStyle` is unlocked in flutter#193774 once `StrutStyle` is applied; `test/painting/text_painter_test.dart: kTextHeightNone unsets the text height multiplier` still fails due to Chromium's integer-rounded `FlutterTest` font metrics at `10px` where `ascent + descent = 11 != 10`). ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [ ] 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 `///`). - [x] 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.  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…ult to proportional (flutter#193736) Part of flutter#193731. Split out of flutter#193403 (third of four independent PRs; the others are flutter#193733 and flutter#193734, and flutter#193403 is stacked on top of this PR). ### Problem - **`TextHeightBehavior.leadingDistribution` was ignored.** `WebParagraphStyle` never passed `textHeightBehavior.leadingDistribution` to the root `WebTextStyle`, and `RootStyleNode._leadingDistribution` always returned `null`, so the value could not reach `LineBlock`. Only an explicit `TextStyle(leadingDistribution: …)` had any effect. - **The default leading distribution was `even`.** `LineBlock` treated `null` the same as `TextLeadingDistribution.even` (half-leading). SkParagraph (and therefore the native engine and CanvasKit) default to `proportional`: `TextStyle::fHalfLeading` is `false` unless `leadingDistribution == even` is set, and `dart:ui`'s `TextHeightBehavior.leadingDistribution` defaults to `TextLeadingDistribution.proportional`. - **Negative half-leading clamped `fontBoundingBoxDescent` to `0.0`.** `TextLine` initialized `fontBoundingBoxAscent` and `fontBoundingBoxDescent` to `0.0` and accumulated every block with `math.max(0.0, ...)`. With `TextLeadingDistribution.even` and a small `height` multiplier (where `height * fontSize < rawAscent + rawDescent`), `extraLeading / 2` is negative and `multipliedFontBoundingBoxDescent` can become negative; `math.max(0.0, ...)` clamped it to `0.0`, inflating the line height above `height * fontSize`. ### Fix - `WebParagraphStyle` propagates `textHeightBehavior?.leadingDistribution` into the root `WebTextStyle`; `RootStyleNode._leadingDistribution` returns `style.leadingDistribution`. Child `TextStyle`s still override it through `ChildStyleNode` as before. - `LineBlock`: `null` now falls through to the `proportional` branch (ascent and descent are scaled by `height * fontSize / (ascent + descent)`), `even` keeps the half-leading behavior. - `TextLine.updateBoundingBox`: track `_hasLineMetrics` so the first block on the line initializes `fontBoundingBoxAscent` and `fontBoundingBoxDescent` directly (preserving a negative `descent`), while subsequent blocks take `math.max`. ### Behavior change For any paragraph with a `height` multiplier and no explicit `leadingDistribution`, the **line height is unchanged** but the **baseline moves**: the extra leading is now split in proportion to the font's ascent/descent instead of 50/50. This brings WebParagraph in line with CanvasKit/Skwasm output for the same `ParagraphStyle`; WebParagraph is not the default renderer yet, so no app-facing change on stable. ### Tests - New `paragraph_line_height_test.dart`: - `Height multiplier scales ascent and descent proportionally by default` — checks the scaled line keeps `height * fontSize`, that ascent/descent scale by the same factor by default, that `TextHeightBehavior(leadingDistribution: even)` adds equal leading on both sides, and that the two differ. Fails on `master` (default was `even` and the THB value was ignored). - `Half-leading with a small height multiplier preserves negative descent` — checks that `height: 0.1` with `TextLeadingDistribution.even` keeps a negative `descent` and total height `0.1 * fontSize`. - Existing `webparagraph/*` and `ui/paragraph_builder_test.dart` suites pass. - **WebParagraph corpus (`preferWebParagraph` + `forceTestFonts` vs `origin/master` `b7315d76579e`)**: **0 fixed standalone, +2 new tests passing, 0 regressions** (base of the flutter#193736 -> flutter#193773 -> flutter#193774 -> flutter#193403 stack that fixes **34** corpus tests; framework `TextPainter line-height` tests in `test/painting/text_painter_test.dart` also call `getBoxesForSelection` with `BoxHeightStyle.tight` and are unlocked when combined with flutter#193734). ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [ ] 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 `///`). - [x] 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.  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…boxes (flutter#193734) Part of flutter#193731. Split out of flutter#193403 (second of four independent PRs; the others are flutter#193733 and flutter#193736, and flutter#193403 itself will be rebased on top once these land). ### Problem - **Placeholder vertical position was computed too early.** `PlaceholderBlock.calculatePlaceholderTop` set `block.advance` from the line ascent *as it was at that moment* before folding `block.ascent` into the line. A placeholder taller than the preceding text (or a later, taller placeholder on the same line) grew `line.fontBoundingBoxAscent` afterwards in `line.updateBoundingBox(block)`, leaving placeholder `advance.top` positioned against a stale ascent. `getBoxesForPlaceholders` returned those stale rects, so a placeholder box could sit above the line's top (negative `top`) and disagree with `getBoxesForRange` for the same range. - **`BoxHeightStyle.tight` returned the height-scaled box for text.** `getBoxesForRange` used `multipliedFontBoundingBoxAscent` / `multipliedHeight`, i.e. the box included the extra leading added by `TextStyle.height`. SkParagraph's `TextLine::getRectsForRange` returns the unscaled glyph bounds for `tight` (`Rect::MakeXYWH(..., -run.ascent(), ..., run.descent())` relative to the baseline). The same code path was also applied to `PlaceholderBlock`, whose `advance` is already line-relative, producing a double-shifted box. ### Fix - `PlaceholderBlock` & `addLine`: split placeholder layout into two passes: - Pass 1 calls `block.calculatePlaceholderMetrics(line.fontBoundingBoxAscent, line.fontBoundingBoxDescent)` to compute each placeholder's `ascent`/`descent` and folds them into the line metrics via `line.updateBoundingBox(block)`. - Pass 2, after `line.fontBoundingBoxAscent` is final, calls `block.calculatePlaceholderTop(line.fontBoundingBoxAscent)` to compute `top = lineAscent - ascent` and set `block.advance = Rect.fromLTWH(spanShiftFromLineStart, top, span.width, span.height)`. - `getBoxesForRange`, `BoxHeightStyle.tight`: - `TextBlock`: `top = line.advance.top + line.fontBoundingBoxAscent - block.rawFontBoundingBoxAscent`, `height = rawFontBoundingBoxAscent + rawFontBoundingBoxDescent` (unscaled glyph bounds positioned at the baseline, matching SkParagraph). - `PlaceholderBlock`: `top = firstRect.top + line.advance.top`, `height = span.height` — `block.advance` is already relative to the line, so no extra ascent shift. - Removed the unused vertical `.translate(...)` on `firstRect` for `TextBlock`, since `firstRect` only provides `left` and `width` while `top` and `bottom` are computed per `BoxHeightStyle`. ### Tests - `paragraph_get_boxes_test.dart`: - `getBoxesForRange and getBoxesForPlaceholders return matching boxes for placeholders` — two placeholders on one line where the second is taller; checks both APIs agree, `top >= 0`, and the box sizes equal the placeholder sizes. On `master`: `getBoxesForPlaceholders` returns `(0, -12, 50, 18)` for the first placeholder while `getBoxesForRange(0, 1)` returns `(0, 14, 50, 44)`. - `BoxHeightStyle.tight uses unscaled glyph height and respects TextHeightBehavior` — `height: 3.0` with `even` leading; `tight` box height equals the unscaled line height and is centered in the 60px line. On `master` the `tight` box is 60px tall instead of 22px. - Existing `paragraph_get_boxes_test.dart` and `paragraph_placeholders_test.dart` pass. - **Full WebParagraph corpus (`--full`, `preferWebParagraph` + `forceTestFonts` vs `origin/master` `b7315d76579e`)**: - Part 1 (`web_ui`): `16/16` `webparagraph/*` (`+198 ~5 -1`, **+2** new tests passing) + `60/60` `test/ui/*` (`+1354 ~5 -41`). - Part 2 (`packages/flutter`, `894/894` suites across `8/8` shards): `+16712 ~1237 -459` vs baseline `+16710 ~1237 -461` (**+3** existing tests fixed; **1** apparent golden diff in `test/cupertino/text_field_test.dart: Overflow clipBehavior none golden` where on `origin/master` two bugs cancelled out — missing `StrutStyle(forceStrutHeight: true)` from flutter#193774 inflated the line ascent by 83px while the old single-pass `calculatePlaceholderTop` shifted the placeholder by `-83px` detached from its `'Hi'` text; resolved once flutter#193774 lands). - Jointly with flutter#193736 + flutter#193773 also unlocks `test/painting/text_painter_test.dart: TextPainter line-height half-leading with leading trim`. <details> <summary>Fixed corpus tests vs <code>origin/master</code> (3)</summary> - `packages/flutter` :: `test/painting/text_painter_test.dart: TextPainter line-height TextLeadingDistribution falls back to paragraph style` - `packages/flutter` :: `test/painting/text_painter_test.dart: TextPainter line-height half-leading` - `packages/flutter` :: `test/painting/text_painter_test.dart: TextPainter widget span` </details> ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [ ] 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 `///`). - [x] 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.  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Rusino added engine flutter/engine related. See also e: labels. platform-web Web applications specifically team-web Owned by Web platform team labels Oct 2, 2026

[web_paragraph] Honor TextHeightBehavior.leadingDistribution and defa…

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…ult to proportional

Rusino force-pushed the webparagraph_leading_distribution branch from cc98644 to 786ba7d Compare October 3, 2026 03:01

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[web_paragraph] Honor TextHeightBehavior.applyHeightToFirstAscent and applyHeightToLastDescent #193773

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[web_paragraph] Apply StrutStyle to line metrics and placeholders #193774

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Merge branch 'master' into webparagraph_leading_distribution

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Comment thread engine/src/flutter/lib/web_ui/lib/src/engine/web_paragraph/layout.dart Resolved

Comment thread engine/src/flutter/lib/web_ui/lib/src/engine/web_paragraph/layout.dart Resolved

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Add trailing periods to comments per Effective Dart

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Merge branch 'master' into webparagraph_leading_distribution

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Merge branch 'master' into webparagraph_leading_distribution

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Merge branch 'master' into webparagraph_leading_distribution

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Cover TextStyle.leadingDistribution overriding TextHeightBehavior

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Test that a child TextStyle's leadingDistribution takes precedence over the paragraph's TextHeightBehavior.leadingDistribution. Assisted-by: Gemini 3.8 Flash (High)

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[web_paragraph] Honor TextHeightBehavior.leadingDistribution and default to proportional - #193736

[web_paragraph] Honor TextHeightBehavior.leadingDistribution and default to proportional#193736
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