UniformGrid: Round measured cell sizes when UseLayoutRounding is enabled

[Soar360]

What does the pull request do?

When UseLayoutRounding is enabled, round the measured cell sizes in UniformGrid to avoid pixel-alignment issues.

Reference file:

• src/Avalonia.Controls/Primitives/UniformGrid.cs

What is the current behavior?

With UseLayoutRounding set to true, UniformGrid didn't apply layout rounding during the measure pass, causing pixel alignment artifacts and small layout offsets.

What is the updated/expected behavior with this PR?

Apply layout rounding to the calculated cell width/height during measurement when UseLayoutRounding is enabled so measurements match the final layout.

How to test:

1. Compare a UniformGrid layout with fractional per-cell sizes and ColumnSpacing/RowSpacing with UseLayoutRounding = true and false.
2. Verify that children.Measure receives the same available size as before (no rounding) and that final arranged cells align cleanly when UseLayoutRounding is true.

How was the solution implemented (if it's not obvious)?

• Kept computation of childAvailableSize and passed it unmodified to child.Measure(childAvailableSize).
• After measuring all children and computing maxWidth/maxHeight from DesiredSize, added a conditional block:
  • if (UseLayoutRounding) then if the value is finite (not Infinity/NaN) call Math.Round on maxWidth and maxHeight.
• Compute totalWidth/totalHeight using potentially-rounded maxWidth/maxHeight as before.
• Left ArrangeOverride in place; it still computes per-cell width/height from finalSize and applies Math.Round there when UseLayoutRounding is true.
• Added a short code comment explaining that rounding is applied to measured max sizes to avoid changing measurement inputs to children.

Implementation notes:

• Uses Math.Round and guards with !double.IsInfinity(...) && !double.IsNaN(...), matching existing repository style.
• No other files modified.

Checklist

• Added unit tests (if possible)?

Breaking changes

• None expected. This changes internal measurement rounding behavior only when UseLayoutRounding is enabled; it avoids changing how children are measured but changes the MeasureOverride return value to be pixel-aligned when rounding is enabled.

Obsoletions / Deprecations

• None.

Fixed issues

• None specific. (If you have a related issue number, add: Fixes #)

[avaloniaui-bot]

You can test this PR using the following package version. 12.0.999-cibuild0059692-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[cla-avalonia]

• All contributors have signed the CLA.

[Soar360]

@cla-avalonia agree

[MrJul]

Thank you. This absolutely needs an unit test.

[MrJul]

Nit: use !MathUtilities.IsFinite() instead (I'm leaving this once, but this applies to the 4 added if conditions).

[MrJul]

This doesn't seem right, we normally use LayoutHelper.RoundLayoutXxx methods with a scale to adjust for the current DPI.

[MrJul]

Reading the comment, I understand that it's now possible for the child control size not to match the grid, which would be unexpected (controls won't be uniform anymore).

Could you please provide a sample to compare the before and after behaviors?
Plus, a matching unit test is needed.

[avaloniaui-bot]

You can test this PR using the following package version. 12.0.999-cibuild0059714-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[avaloniaui-bot]

You can test this PR using the following package version. 12.0.999-cibuild0059718-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[avaloniaui-bot]

You can test this PR using the following package version. 12.0.999-cibuild0059782-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[avaloniaui-bot]

You can test this PR using the following package version. 12.0.999-cibuild0059990-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]