Avoid unnecessary work in `BoxDecoration` and `RenderPhysicalModel` by bernaferrari · Pull Request #187891 · flutter/flutter

bernaferrari · 2026-06-11T21:59:42Z

Part of https://github.com//issues/187894

Improve box_decoration.dart

In Flutter’s codebase that pattern already exists in similar hit-test code (RenderClipOval.hitTest

flutter/packages/flutter/lib/src/rendering/proxy_box.dart

Line 1932 in 8c17c5e

// x^2 + y^2 > r^2

).

Old code:

final double distance = (position - center).distance;
return distance <= math.min(size.width, size.height) / 2.0;

Offset.distance computes: sqrt(dx * dx + dy * dy)

New code:

final double radius = math.min(size.width, size.height) / 2.0;
return (position - center).distanceSquared <= radius * radius;

Offset.distanceSquared computes only: dx * dx + dy * dy
Then it compares that to radius * radius.
Mathematically: sqrt(dx² + dy²) <= r is equivalent to: dx² + dy² <= r²

Then, I also found an issue: elevated shadow path doesn't need to be initialized when there is no elevation to use it for.

gemini-code-assist

Code Review

This pull request optimizes 'BoxDecoration.hitTest' for circular shapes by using squared distance to avoid square root calculations, and defers the creation of 'offsetRRectAsPath' in 'RenderPhysicalModel.paint' to only occur when elevation is non-zero. It also adds corresponding unit tests for both modifications. Feedback on the changes points out that the new test in 'proxy_box_test.dart' uses a non-standard matcher 'paintsExactlyCountTimes' which will cause compilation failure, and suggests refactoring it to use the standard 'paints' matcher.

gemini-code-assist · 2026-06-11T22:00:44Z

+    expect(
+      (PaintingContext context, Offset offset) => root.paint(context, offset),
+      paintsExactlyCountTimes(#drawShadow, 0),
+    );
+
+    root.elevation = 1.0;
+    pumpFrame(phase: EnginePhase.paint);
+    expect(
+      (PaintingContext context, Offset offset) => root.paint(context, offset),
+      paintsExactlyCountTimes(#drawShadow, 1),
+    );


The matcher paintsExactlyCountTimes is not a standard matcher in the Flutter test framework, which will cause this test to fail to compile. Instead, use the standard paints matcher from package:flutter_test to assert whether a shadow is painted or not. This is more idiomatic, concise, and avoids custom matchers.

Suggested change

expect(

(PaintingContext context, Offset offset) => root.paint(context, offset),

paintsExactlyCountTimes(#drawShadow, 0),

);

root.elevation = 1.0;

pumpFrame(phase: EnginePhase.paint);

expect(

(PaintingContext context, Offset offset) => root.paint(context, offset),

paintsExactlyCountTimes(#drawShadow, 1),

);

expect(root, isNot(paints..shadow()));

root.elevation = 1.0;

pumpFrame(phase: EnginePhase.paint);

expect(root, paints..shadow());

You are wrong.

paintsExactlyCountTimes is part of Flutter’s test framework: it is exported by package:flutter_test/flutter_test.dart from src/mock_canvas.dart. It is also already used elsewhere in this file and throughout the Flutter test suite.

I’m keeping it here because this test is specifically verifying the number of drawShadow calls: zero at elevation 0, and one when elevation is non-zero. Analyzer and the focused test pass on the current base.
paintsExactlyCountTimes is exported by package:flutter_test/flutter_test.dart:
packages/flutter_test/lib/flutter_test.dart exports src/mock_canvas.dart, and src/mock_canvas.dart defines paintsExactlyCountTimes.

We can check if CI/CD passes, then.

flutter-dashboard · 2026-07-01T23:40:58Z

This pull request executed golden file tests, but it has not been updated in a while (20+ days). Test results from Gold expire after as many days, so this pull request will need to be updated with a fresh commit in order to get results from Gold.

For more guidance, visit Writing a golden file test for package:flutter.

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

Renzo-Olivares

LGTM, thank you for the contribution!

justinmc

LGTM 👍 . Thanks for improving performance @bernaferrari!

justinmc · 2026-07-28T22:47:58Z

-        final double distance = (position - center).distance;
-        return distance <= math.min(size.width, size.height) / 2.0;
+        final double radius = math.min(size.width, size.height) / 2.0;
+        // Comparing squared distances avoids computing sqrt(dx * dx + dy * dy).


auto-submit · 2026-07-28T22:49:15Z

autosubmit label was removed for flutter/flutter/187891, because The base commit of the PR is older than 7 days and can not be merged. Please merge the latest changes from the main into this branch and resubmit the PR.

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Avoid sqrt in gesture distance checks #187895

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Avoid unnecessary work in BoxDecoration and RenderPhysicalModel

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Avoid unnecessary work in `BoxDecoration` and `RenderPhysicalModel` - #187891

Avoid unnecessary work in `BoxDecoration` and `RenderPhysicalModel`#187891
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