WPF rectangle - round just top corners - wpf

Question

How can I have just the top corners rounded for a WPF rectangle?
I created a border and set the CornerRadius property and inside the border I've added my rectangle, but it doesn't work, the rectangle is not rounded.
<Border BorderThickness="1" CornerRadius="50,50,0,0" BorderBrush="Black">
<Rectangle Fill="#FF5A9AE0" Stretch="UniformToFill" ClipToBounds="True"/>
</Border>

Answer 1

The problem you've got is that the rectangle is "overflowing" the rounded corners of your border.
A rectangle can't have individually rounded corners, so if you just put the background colour on the border and remove the rectangle:
<Border BorderThickness="1" Grid.Row="0" Grid.ColumnSpan="2"
CornerRadius="50,50,0,0" BorderBrush="Black" Background="#FF5A9AE0">
</Border>
You'll get your desired effect.

Answer 2

Set the RadiusX and RadiusY properties on the rectangle, this will give it rounded corners

Answer 3

Good example how its possible to do OnRender with DrawingContext:
/// <summary>
/// Draws a rounded rectangle with four individual corner radius
/// </summary>
public static void DrawRoundedRectangle(this DrawingContext dc, Brush brush,
Pen pen, Rect rect, CornerRadius cornerRadius)
{
var geometry = new StreamGeometry();
using (var context = geometry.Open())
{
bool isStroked = pen != null;
const bool isSmoothJoin = true;
context.BeginFigure(rect.TopLeft + new Vector(0, cornerRadius.TopLeft), brush != null, true);
context.ArcTo(new Point(rect.TopLeft.X + cornerRadius.TopLeft, rect.TopLeft.Y),
new Size(cornerRadius.TopLeft, cornerRadius.TopLeft),
90, false, SweepDirection.Clockwise, isStroked, isSmoothJoin);
context.LineTo(rect.TopRight - new Vector(cornerRadius.TopRight, 0), isStroked, isSmoothJoin);
context.ArcTo(new Point(rect.TopRight.X, rect.TopRight.Y + cornerRadius.TopRight),
new Size(cornerRadius.TopRight, cornerRadius.TopRight),
90, false, SweepDirection.Clockwise, isStroked, isSmoothJoin);
context.LineTo(rect.BottomRight - new Vector(0, cornerRadius.BottomRight), isStroked, isSmoothJoin);
context.ArcTo(new Point(rect.BottomRight.X - cornerRadius.BottomRight, rect.BottomRight.Y),
new Size(cornerRadius.BottomRight, cornerRadius.BottomRight),
90, false, SweepDirection.Clockwise, isStroked, isSmoothJoin);
context.LineTo(rect.BottomLeft + new Vector(cornerRadius.BottomLeft, 0), isStroked, isSmoothJoin);
context.ArcTo(new Point(rect.BottomLeft.X, rect.BottomLeft.Y - cornerRadius.BottomLeft),
new Size(cornerRadius.BottomLeft, cornerRadius.BottomLeft),
90, false, SweepDirection.Clockwise, isStroked, isSmoothJoin);
context.Close();
}
dc.DrawGeometry(brush, pen, geometry);
}
Information from:
http://wpftutorial.net/DrawRoundedRectangle.html

Answer 4

This one will work even with Rectangle (or anything else) inside it:
<Border>
<Border.OpacityMask>
<VisualBrush>
<VisualBrush.Visual>
<Border CornerRadius="5" Height="100" Width="100" Background="White"/>
</VisualBrush.Visual>
</VisualBrush>
</Border.OpacityMask>
// put your rounded content here
</Border>
You will have to play with Height and Width if you do not have exact size of content.