InkToolbar: honour CornerRadius and Padding in the control template

[Nitin Chaudhary (Nitin-100)]

Problem

CornerRadius has no effect on InkToolbar. Reported against the experimental release.

The template root binds Background, BorderBrush and BorderThickness, but not CornerRadius — so the property is silently ignored. Padding has the same latent gap and is fixed here too.

https://github.com/microsoft/microsoft-ui-xaml/blob/main/controls/dev/InkToolbar/InkToolbar.xaml#L1549

Fix

Bind both through on the template root. StackPanel supports CornerRadius and Padding (see microsoft.ui.xaml.controls.controls.idl), so no structural change is needed.

-<StackPanel x:Name="Panel" Orientation="Horizontal" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Margin="2,2,2,2" />
+<StackPanel x:Name="Panel" Orientation="Horizontal" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="{TemplateBinding CornerRadius}" Padding="{TemplateBinding Padding}" Margin="2,2,2,2" />

Note for reviewers: this deviates from UWP

Worth calling out explicitly, since the inking work has been held to strict UWP parity.

The UWP InkToolbar template omits these same two bindings — verified identical in Windows SDK 10.0.19041.0 and 10.0.26100.0:

<ControlTemplate TargetType="InkToolbar">
  <StackPanel x:Name="Panel" Orientation="Horizontal"
              Background="{TemplateBinding Background}"
              BorderBrush="{TemplateBinding BorderBrush}"
              BorderThickness="{TemplateBinding BorderThickness}" />
</ControlTemplate>

So this is not a port regression — it is a long-standing UWP gap we inherited faithfully. Control.CornerRadius postdates InkToolbar (RS5 vs 1607), which is likely why it was never wired up. WinUI 3's rounded design language makes callers reasonably expect it to work, so fixing it here is an intentional improvement rather than an oversight.

The change is purely additive: templates that never set CornerRadius/Padding are unaffected, since both default to zero.

Validation

With the template applied to an InkToolbar with CornerRadius="12":

• InkToolbar.CornerRadius → 12 and the template root now receives 12 (previously 0)
• The border renders rounded; before the change the same markup rendered square
• No functional regression: tool selection, flyouts, orientation switching and ink capture all behave as before

Verified on an unpackaged WinUI 3 desktop app against a local product build.

[Pranav Gupta (pranav-gupta-msft)]

For Accessibility

[Harshit (harshit7962)]

LGTM

[Nitin Chaudhary (Nitin-100)]

/azp run

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