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[cupertino_ui] Fix CupertinoMagnifier focal point with custom size - #13029
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CupertinoMagnifier computed its focal point offset from kDefaultSize instead of the size it was given, so magnifiers with a custom size did not center the magnified content vertically. Fixes flutter/flutter#151740
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This pull request updates CupertinoMagnifier to calculate its focal point offset using its actual size instead of kDefaultSize, and adds a corresponding widget test. Feedback points out that Offset is immutable, meaning the call to focalPointOffset.scale(...) does not mutate the variable and the animation scale is currently ignored. A correction is suggested to apply the scale directly during initialization.
| @override | ||
| Widget build(BuildContext context) { | ||
| var focalPointOffset = Offset(0, (kDefaultSize.height / 2) - kMagnifierAboveFocalPoint); | ||
| var focalPointOffset = Offset(0, (size.height / 2) - kMagnifierAboveFocalPoint); |
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The Offset class in Flutter is immutable. Calling focalPointOffset.scale(...) on line 357 returns a new Offset but does not mutate the existing one, meaning the animation scale is currently ignored. To fix this, you can apply the scale directly during the initialization of focalPointOffset on this line, and then remove the redundant focalPointOffset.scale(...) call on line 357.
var focalPointOffset = Offset(0, ((size.height / 2) - kMagnifierAboveFocalPoint) * (inOutAnimation?.value ?? 1));
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Could you take a look at this comment from Gemini? It seems to be an existing issue, so I'm not sure if we should fix it here or create a separate issue for it.
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Thanks for pointing it out! You're right, scale is a no-op because Offset is immutable, but it was already like that before this PR. Fixing it would change the in/out animation of every CupertinoMagnifier, not only custom sizes, so I think it's better handled in a separate issue. I'm happy to open one and work on it.
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CupertinoMagnifierusedkDefaultSize.heightinstead ofsize.heightto compute its focal point, so magnified content was not vertically centered with a customsize. The default size is unchanged.Fixes flutter/flutter#151740
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