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[flutter_svg] Update README with an example to scale images #10547

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[flutter_svg] Update README with an example to scale images #10547

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df3271f
Update flutter_svg README with an example to scale images
androidseb Dec 1, 2025
1618e26
Extracted scaling example into its own dedicated example section
androidseb Dec 7, 2025
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37 changes: 37 additions & 0 deletions third_party/packages/flutter_svg/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -127,6 +127,43 @@ import 'dart:ui' as ui;
pictureInfo.picture.dispose();
```

or if you want to scale it, you can do something like:

<?code-excerpt "example/lib/readme_excerpts.dart (OutputScaling)"?>
```dart
import 'dart:ui' as ui;

// ···
const rawSvg = '''<svg ...>...</svg>''';
final PictureInfo pictureInfo = await vg.loadPicture(
const SvgStringLoader(rawSvg),
null,
);

// You can convert the picture to a scaled image:
const double targetWidth = 512;
const double targetHeight = 512;
final pictureRecorder = ui.PictureRecorder();
final canvas = Canvas(
pictureRecorder,
Rect.fromPoints(
Offset.zero,
const Offset(targetWidth, targetHeight),
),
);
canvas.scale(
targetWidth / pictureInfo.size.width,
targetHeight / pictureInfo.size.height,
);
canvas.drawPicture(pictureInfo.picture);
final ui.Image scaledImage = await pictureRecorder.endRecording().toImage(
targetWidth.ceil(),
targetHeight.ceil(),
);

pictureInfo.picture.dispose();
```
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@stuartmorgan-g stuartmorgan-g Jan 6, 2026

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This is adding a lot of code length to the README, and a lot of it is duplicated from above, or is about PictureRecorder rather than flutter_svg. Do we actually need to document anything other than the need to call scale to make it clear how to do this?

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@androidseb androidseb Jan 8, 2026

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To keep the example code footprint smaller, I could keep the current example and just add two lines like so:

  // You can scale the canvas to achieve lossless vector image stretching before drawing it
  canvas.scale(1.2, 1.2);
  // You can draw the picture to a canvas:
  canvas.drawPicture(pictureInfo.picture);

Would that be better maybe?


The `SvgPicture` helps to automate this logic, and it provides some convenience
wrappers for getting assets from multiple sources.

Expand Down
37 changes: 37 additions & 0 deletions third_party/packages/flutter_svg/example/lib/readme_excerpts.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -6,9 +6,11 @@
// intended for use as an actual example application.

// #docregion OutputConversion
// #docregion OutputScaling
import 'dart:ui' as ui;

// #enddocregion OutputConversion
// #enddocregion OutputScaling

import 'package:flutter/material.dart';
import 'package:flutter_svg/flutter_svg.dart';
Expand Down Expand Up @@ -101,6 +103,41 @@ Future<ui.Image> convertSvgOutput() async {
return image;
}

/// Demonstrates scaling SVG to a larger image
Future<ui.Image> scaleSvgOutput() async {
// #docregion OutputScaling
const rawSvg = '''<svg ...>...</svg>''';
final PictureInfo pictureInfo = await vg.loadPicture(
const SvgStringLoader(rawSvg),
null,
);

// You can convert the picture to a scaled image:
const double targetWidth = 512;
const double targetHeight = 512;
final pictureRecorder = ui.PictureRecorder();
final canvas = Canvas(
pictureRecorder,
Rect.fromPoints(
Offset.zero,
const Offset(targetWidth, targetHeight),
),
);
canvas.scale(
targetWidth / pictureInfo.size.width,
targetHeight / pictureInfo.size.height,
);
canvas.drawPicture(pictureInfo.picture);
final ui.Image scaledImage = await pictureRecorder.endRecording().toImage(
targetWidth.ceil(),
targetHeight.ceil(),
);

pictureInfo.picture.dispose();
// #enddocregion OutputScaling
return scaledImage;
}

// #docregion ColorMapper
class _MyColorMapper extends ColorMapper {
const _MyColorMapper();
Expand Down