StrokeStartLineCap=Square
<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" x:Class="Microsoft.Samples.Graphics.RectangleExample" WindowTitle="Example"> <Canvas> <Polyline Points="50,50 75,30 100,100 130,40" Stroke="Red" StrokeThickness="20" StrokeStartLineCap="Square" StrokeEndLineCap="Square" Grid.Row="2" Grid.Column="4"/> </Canvas> </Page>