[Spec] Rounded Corners

[jsuarezruiz]

Rounded Corners

Rounded Corners are a common visual requirement.

API

We need to add an interface for defining what's required for a View to implement corner rounding (and provide CSS support):

interface IRoundedCorner
{
	CornerRadius CornerRadius { get; }
	void CornerRadiusChanged(CornerRadius oldValue, CornerRadius newValue);
}

The CornerRadius BindableProperty can be implemented in one place:

static class RoundedCorner
{
	public static readonly BindableProperty CornerRadiusProperty = 
	     BindableProperty.Create(nameof(CornerRadius), typeof(CornerRadius), typeof(IRoundedCorners));
}

The following Views are candidates for rounded corners:

• BoxView
• Button
• Image
• ImageButton
• Layouts
• ScrollView

Scenarios

C# Example

var grid = new Grid();
grid.CornerRadius = new CornerRadius(12, 0, 12, 6);

XAML Example

<Grid
     CornerRadius="12, 0, 12, 6">
</Grid>

Difficulty: Medium

Providing the interface is simple; individual implementations may vary in difficulty.

[aguywithcode]

Looks like Button has a CornerRadiusProperty already. Perhaps it should be extracted to a higher class in the tree perhaps View or VisualElement?

[ederbond]

Also make sure that if the element is set to have shadow, the shadow should be rounded too.
I've opened some issues for this in the past too. xamarin/Xamarin.Forms#3867
and here xamarin/Xamarin.Forms#3871

[MitchBomcanhao]

Would the rounded corners clip the content of the control?

[themronion]

What about single rounded corners on frame - like PancakeView? I think this is more desirable and wanted by xamarin devs. Thumbs up who agrees!