Paragraph.getLineBoundary doesn't consider TextAffinity

ui.Paragraph.getLineBoundary gives an incorrect response when passed TextAffinity.downstream at a line wrap.

Example

Imagine we're rendering the string "123456789" and our field is very narrow and so the "9" wraps:

|12345678|
|9       |

There are now two TextPositions between the 8 and the 9, one on the first line and one on the second line:

First line: TextPosition(offset: 8, affinity: TextAffinity.upstream)
Second line: TextPosition(offset: 8, affinity: TextAffinity.downstream)

The problem is that getLineBoundary will return a TextRange of 0-8 regardless of which of the above two TextPositions are passed to it. It doesn't use the TextAffinity, only the index, which you can see in the code here.

@GaryQian

CC @GaryQian Do you have any idea if there was a reason for this, or is this something that we should fix?

I think I've reproduced the issue correctly, let me know if it is missing something

Used the following minimal code sample

complete minimal runnable code sample

import 'dart:async';
import 'dart:typed_data';
import 'dart:ui' as ui;
import 'dart:io';

import 'package:flutter/painting.dart';

Future<ui.Image> getScreenshot() async {
  final screenshotbytes = File('locations.jpg').readAsBytes();

  final Completer<ui.Image> completer = Completer<ui.Image>();
  ui.decodeImageFromList(await screenshotbytes, completer.complete);
  return completer.future;
}

Future<ui.Picture?> paint(ui.Rect paintBounds) async {
  final ui.PictureRecorder recorder = ui.PictureRecorder();

  final ui.Canvas canvas = ui.Canvas(recorder, paintBounds);

  final ui.ParagraphBuilder paragraphBuilder =
      ui.ParagraphBuilder(ui.ParagraphStyle(
    fontSize: 150,
    fontFamily: 'Montserrat-Bold',
    textAlign: TextAlign.center,
  ))
        ..addText('123456789');

  final ui.Paragraph paragraph = paragraphBuilder.build()
    ..layout(ui.ParagraphConstraints(width: paintBounds.size.width - 100));
  canvas.drawParagraph(
      paragraph, Offset(paintBounds.left + 50, paintBounds.top + 100));

  final range1 = paragraph.getLineBoundary(
      TextPosition(offset: 8, affinity: TextAffinity.upstream));

  print(range1);

  final range2 = paragraph.getLineBoundary(
      TextPosition(offset: 8, affinity: TextAffinity.downstream));
  print(range2);

  return recorder.endRecording();
}

ui.Scene composite(ui.Picture picture, ui.Rect bounds) {
  final double devicePixelRatio = ui.window.devicePixelRatio;
  final Float64List deviceTransform = Float64List(16)
    ..[0] = devicePixelRatio
    ..[5] = devicePixelRatio
    ..[10] = 1.0
    ..[15] = 1.0;
  final ui.SceneBuilder sceneBuilder = ui.SceneBuilder()
    ..pushTransform(deviceTransform)
    ..addPicture(ui.Offset.zero, picture)
    ..pop();
  return sceneBuilder.build();
}

void beginFrame(Duration timeStamp) async {
  final ui.Rect paintBounds = ui.Offset.zero & const ui.Size(800, 1920);
  final ui.Picture? picture = await paint(paintBounds);
  final ui.Scene scene = composite(picture!, paintBounds);
  ui.window.render(scene);

  final image = await picture.toImage(1080, 1920);
  final data = await image.toByteData(format: ui.ImageByteFormat.png);
  if (data != null) {
    final buffer = data.buffer;
    File('screenshot_3.png').writeAsBytes(
        buffer.asUint8List(data.offsetInBytes, data.lengthInBytes));
  }
}

void main() {
  ui.window.onBeginFrame = beginFrame;
  ui.window.scheduleFrame();
}

[  +16 ms] flutter: TextRange(start: 0, end: 8)
[        ] flutter: TextRange(start: 0, end: 8)

preview

`stable`	`master`
❌	❌

Check flutter doctor -v outputs for each channel below

flutter doctor -v

[✓] Flutter (Channel stable, 2.2.3, on Microsoft Windows [Version 10.0.22000.120], locale en-US)
    • Flutter version 2.2.3 at C:\Users\Taha\Code\flutter_stable
    • Framework revision f4abaa0735 (6 weeks ago), 2021-07-01 12:46:11 -0700
    • Engine revision 241c87ad80
    • Dart version 2.13.4

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
    • Android SDK at C:\Users\Taha\Code\android-sdk
    • Platform android-30, build-tools 30.0.3
    • ANDROID_SDK_ROOT = C:\Users\Taha\Code\android-sdk
    • Java binary at: C:\Users\Taha\Code\android-studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7249189)
    • All Android licenses accepted.

[✓] Chrome - develop for the web
    • Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe

[✓] Visual Studio - develop for Windows (Visual Studio Community 2019 16.10.4)
    • Visual Studio at C:\Program Files (x86)\Microsoft Visual Studio\2019\Community
    • Visual Studio Community 2019 version 16.10.31515.178
    • Windows 10 SDK version 10.0.19041.0

[!] Android Studio (not installed)
    • Android Studio not found; download from https://developer.android.com/studio/index.html
      (or visit https://flutter.dev/docs/get-started/install/windows#android-setup for detailed instructions).

[✓] VS Code (version 1.59.0)
    • VS Code at C:\Users\Taha\AppData\Local\Programs\Microsoft VS Code
    • Flutter extension version 3.25.0

[✓] Connected device (3 available)
    • Windows (desktop) • windows • windows-x64    • Microsoft Windows [Version 10.0.22000.120]
    • Chrome (web)      • chrome  • web-javascript • Google Chrome 92.0.4515.131
    • Edge (web)        • edge    • web-javascript • Microsoft Edge 92.0.902.67

! Doctor found issues in 1 category.

[✓] Flutter (Channel master, 2.5.0-6.0.pre.40, on Microsoft Windows [Version 10.0.22000.120], locale en-US)
    • Flutter version 2.5.0-6.0.pre.40 at C:\Users\Taha\Code\flutter_master
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 7d76a827c0 (14 hours ago), 2021-08-09 15:21:17 -0700
    • Engine revision 4fef55db10
    • Dart version 2.14.0 (build 2.14.0-385.0.dev)

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
    • Android SDK at C:\Users\Taha\Code\android-sdk
    • Platform android-30, build-tools 30.0.3
    • ANDROID_SDK_ROOT = C:\Users\Taha\Code\android-sdk
    • Java binary at: C:\Users\Taha\Code\android-studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7249189)
    • All Android licenses accepted.

[✓] Chrome - develop for the web
    • Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe

[✓] Visual Studio - develop for Windows (Visual Studio Community 2019 16.10.4)
    • Visual Studio at C:\Program Files (x86)\Microsoft Visual Studio\2019\Community
    • Visual Studio Community 2019 version 16.10.31515.178
    • Windows 10 SDK version 10.0.19041.0

[✓] Android Studio (version 2020.3)
    • Android Studio at C:\Users\Taha\Code\android-studio
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7249189)

[✓] VS Code (version 1.59.0)
    • VS Code at C:\Users\Taha\AppData\Local\Programs\Microsoft VS Code
    • Flutter extension version 3.25.0

[✓] Connected device (4 available)
    • Windows (desktop)       • windows • windows-x64     • Microsoft Windows [Version 10.0.22000.120]
    • Windows (UWP) (desktop) • winuwp  • windows-uwp-x64 •
    • Chrome (web)            • chrome  • web-javascript  • Google Chrome 92.0.4515.131
    • Edge (web)              • edge    • web-javascript  • Microsoft Edge 92.0.902.67

• No issues found!

✅: No Issue ❌: Issue reproduced

@TahaTesser

@TahaTesser Yes thank you for the great repro! I ashamed to say that I assumed it wasn't reproducible without putting print statements in the framework code 😞

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.

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Paragraph.getLineBoundary doesn't consider TextAffinity #87970

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Paragraph.getLineBoundary doesn't consider TextAffinity #87970

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justinmc commented on Aug 9, 2021

TahaTesser commented on Aug 10, 2021

justinmc commented on Aug 10, 2021

github-actions commented on Aug 31, 2021

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