Fix border inner rounded clip by wieslawsoltes · Pull Request #20647 · AvaloniaUI/Avalonia

wieslawsoltes · 2026-02-09T10:29:48Z

PR Summary: Child-Only Layout Clipping, Composition Parity, and Samples

What

Add a child-only layout clip API aligned with WPF UIElement.GetLayoutClip.
Implement rounded inner-edge child clipping for Border and ContentPresenter when ClipToBounds is enabled.
Align immediate rendering, composition rendering, and composition hit-testing with child-only layout clips.
Preserve visual rendering while applying child-only clips (background/border unaffected).
Fix composition rendering parity for BackgroundSizing on Border and ContentPresenter.
Add render tests and expected images for layout-clip geometry and ContentPresenter rounded clipping.
Add render tests and baselines for BackgroundSizing parity.
Add a ControlCatalog "Child Clipping" page with rounded child clip, adorner clip, and geometry layout clip examples.

How

Added Visual.GetLayoutClip(Size layoutSlotSize) and TryGetChildClipCore(...) to provide child-only clips.
Stored the arranged layout slot size in Layoutable.Arrange and used it when computing layout clips.
Border and ContentPresenter override TryGetChildClipCore to return a rounded inner-edge RoundedRect using GeometryBuilder.CalculateRoundedCornersRectangleWinUI with BackgroundSizing.InnerBorderEdge.
Immediate renderer now uses the layout clip around child rendering and keeps the visual clip separate.
Composition serialization carries child clip data; server rendering swaps the clip around children only.
Composition hit testing respects layout clips regardless of ClipToBounds and without clamping to visual bounds.
Composition border visuals now serialize BackgroundSizing to match immediate rendering.

Why

Child content should be clipped to rounded inner edges without clipping the control's own background/border.
WPF-aligned GetLayoutClip behavior should be based on layout slot size and independent from ClipToBounds.
Consistent behavior across immediate and composition render paths is required to avoid visual mismatches.

Behavioral Notes

GetLayoutClip affects only children; the visual's own rendering is not clipped.
ClipToBounds = true on Border/ContentPresenter yields rounded inner-edge child clipping.
ClipToBounds = false does not prevent layout clips provided by GetLayoutClip.
Composition and immediate renderers follow the same child-only clip semantics.

Test Coverage

GeometryChildClip_Clips_Child
GeometryChildClip_Clips_When_ClipToBounds_False
GeometryChildClip_Uses_LayoutSlotSize
ContentPresenter_RoundedClip_Clips_Child
Border_BackgroundSizing_OuterBorderEdge
ContentPresenter_BackgroundSizing_OuterBorderEdge
New expected images added for the above render tests.

Sample Coverage

ControlCatalog "Child Clipping" page shows:
- Rounded child clipping for Border.
- Rounded child clipping for ContentPresenter.
- Adorner clipping respecting rounded bounds.
- Geometry layout clip example that works without ClipToBounds.

Fixes #2105

avaloniaui-bot · 2026-02-09T11:28:59Z

You can test this PR using the following package version. 12.0.999-cibuild0062051-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

avaloniaui-bot · 2026-02-09T13:10:08Z

You can test this PR using the following package version. 12.0.999-cibuild0062055-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

robloo · 2026-02-10T19:04:48Z

Awesome! Thanks so much for picking this up. Will definitely dig into the details for my own experience as well.

robloo · 2026-02-10T19:18:41Z

src/Avalonia.Controls/Border.cs

+        bool IVisualWithChildClip.TryGetChildClip(out RoundedRect clip)
+        {
+            var bounds = new Rect(Bounds.Size);
+            var keypoints = GeometryBuilder.CalculateRoundedCornersRectangleWinUI(
+                bounds,
+                LayoutThickness,
+                CornerRadius,
+                BackgroundSizing.InnerBorderEdge);
+            clip = keypoints.ToRoundedRect();
+            return true;
+        }


I know this is still draft so won't comment heavily. But should we try to support ALL geometries rather than just RoundedRect here? If someone creates a star-shaped control and needs to clip children this API won't work.

Note: The geometries can get crazy even in WinUI but I guess theoretically for a border are always some form of RoundedRect.

Note: We also need to support clipping in ContentPresenter

Also note WPF supports arbitrary geometry here as well: https://learn.microsoft.com/en-us/dotnet/api/system.windows.uielement.getlayoutclip

Attempted to implement it more broadly:

e14a377
05dbca2
0381cc5
17c2186
e143822

robloo · 2026-02-10T19:23:14Z

src/Avalonia.Controls/BorderVisual.cs

        }
    }

+    public Thickness BorderThickness


Side comment: BackgroundSizing should be added too I think for border visuals to render the same. This is unrelated to the changes here though.

Well we can try to do this here I guess:

eca2032

c8d0f00

…rounded-clip

avaloniaui-bot · 2026-02-10T20:28:25Z

You can test this PR using the following package version. 12.0.999-cibuild0062115-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

avaloniaui-bot · 2026-02-11T21:35:54Z

You can test this PR using the following package version. 12.0.999-cibuild0062186-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

wieslawsoltes added 6 commits February 9, 2026 11:25

Add child-only clip support for Border

9fcdacd

Add render tests for Border clipping

a2b1776

Update Border sample for clipping examples

45be70d

Merge upstream/master

6fcbdb7

Use PushClipToBounds in composition rendering

8bdeee9

Refactor BorderVisual child clip swap

e8654f5

Fix adorner rounded clip and add render test

65b40f5

robloo mentioned this pull request Feb 10, 2026

Support Clipping to rounded corners #2105

Open

robloo reviewed Feb 10, 2026

View reviewed changes

Merge remote-tracking branch 'upstream/master' into fix/border-inner-…

c662479

…rounded-clip

wieslawsoltes added 8 commits February 10, 2026 22:59

Add layout clip API and track slot size

e14a377

Plumb child layout clips through rendering

05dbca2

Add rounded child clipping for Border and ContentPresenter

0381cc5

Add ControlCatalog child clipping samples

17c2186

Add render tests and baselines for child clips

e143822

Sync BackgroundSizing in composition border visuals

eca2032

Add render tests for BackgroundSizing parity

c8d0f00

Merge branch 'master' into fix/border-inner-rounded-clip

72976b7

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Fix border inner rounded clip#20647

Fix border inner rounded clip#20647
wieslawsoltes wants to merge 16 commits intoAvaloniaUI:masterfrom
wieslawsoltes:fix/border-inner-rounded-clip

wieslawsoltes commented Feb 9, 2026 •

edited

Loading

Uh oh!

avaloniaui-bot commented Feb 9, 2026

Uh oh!

avaloniaui-bot commented Feb 9, 2026

Uh oh!

robloo commented Feb 10, 2026

Uh oh!

robloo Feb 10, 2026 •

edited

Loading

Uh oh!

robloo Feb 10, 2026 •

edited

Loading

Uh oh!

wieslawsoltes Feb 10, 2026

Uh oh!

robloo Feb 10, 2026

Uh oh!

wieslawsoltes Feb 10, 2026

Uh oh!

avaloniaui-bot commented Feb 10, 2026

Uh oh!

avaloniaui-bot commented Feb 11, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Uh oh!

Conversation

wieslawsoltes commented Feb 9, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

PR Summary: Child-Only Layout Clipping, Composition Parity, and Samples

What

How

Why

Behavioral Notes

Test Coverage

Sample Coverage

Uh oh!

avaloniaui-bot commented Feb 9, 2026

Uh oh!

avaloniaui-bot commented Feb 9, 2026

Uh oh!

robloo commented Feb 10, 2026

Uh oh!

robloo Feb 10, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

robloo Feb 10, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

wieslawsoltes Feb 10, 2026

Choose a reason for hiding this comment

Uh oh!

robloo Feb 10, 2026

Choose a reason for hiding this comment

Uh oh!

wieslawsoltes Feb 10, 2026

Choose a reason for hiding this comment

Uh oh!

avaloniaui-bot commented Feb 10, 2026

Uh oh!

avaloniaui-bot commented Feb 11, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

wieslawsoltes commented Feb 9, 2026 •

edited

Loading

robloo Feb 10, 2026 •

edited

Loading

robloo Feb 10, 2026 •

edited

Loading