WPF anti-aliasing artifacts

Question

I have a weird rendering problem when I try to use smooth graphics in WPF.

Here is a simplified version.

If I use the following XAML

<Window x:Class="RenderingBug.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="Window1" Width="300" Height="300">
    <Grid Name="myGrid" Background="AntiqueWhite" Width="250" Height="250">
        <ScrollViewer Name="myScrollViewer" HorizontalScrollBarVisibility="Auto" VerticalScrollBarVisibility="Auto">
            <Canvas Height="500" Width="500" Name="myCanvas" />
        </ScrollViewer>        
    </Grid>
 </Window>

And the following cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace RenderingBug
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();

            PathFigureCollection pfc = new PathFigureCollection();
            PathFigure pf = new PathFigure();
            pf.StartPoint = new Point(100, 20);
            LineSegment ls = new LineSegment();
            ls.Point = new Point(20, 100);
            PathSegmentCollection psc = new PathSegmentCollection();
            psc.Add(ls);
            pf.Segments = psc;
            pfc.Add(pf);
            PathGeometry pg = new PathGeometry(pfc);

            RectangleGeometry clippingRectangle = new RectangleGeometry(new Rect(0, 0, 80, 80));

            Path p1 = new Path();
            p1.ClipToBounds = true;
            p1.Clip = clippingRectangle;
            p1.StrokeDashCap = PenLineCap.Square;
            p1.Stroke = Brushes.Black;
            p1.StrokeThickness = 30;
            p1.Data = pg;
            myCanvas.Children.Add(p1);

            Path p2 = new Path();
            p2.ClipToBounds = true;
            p2.Clip = clippingRectangle;
            p2.StrokeDashCap = PenLineCap.Square;
            p2.Stroke = Brushes.White;
            p2.StrokeThickness = 10;
            p2.Data = pg;
            myCanvas.Children.Add(p2);
        }
    }
}

I get a weird rendering problem with smoothing where the edge of the crop rectangle is (the program is running, it will be pretty obvious, but it's a foggy gray line where the crop rectangle cuts the paths.)

I tried various methods such as aligning the controls to specific pixels and setting SnapsToDevicePixels to various controls in the hope that this will solve this problem (remove the extra foggy gray stripe) but nothing helps.

Any ideas?

Answer 1

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private void workingAreaScrollViewer_SizeChanged(object sender, SizeChangedEventArgs e)
{
    double w = e.NewSize.Width;
    double h = e.NewSize.Height;
    workingAreaScrollViewer.Width = Math.Round(w);
    workingAreaScrollViewer.Height = Math.Round(h);
}

private void Window_KeyDown(object sender, KeyEventArgs e)
{
    if (e.Key == Key.A)
    {
        workingAreaCanvas.Children.Remove(p2);
    }
    if (e.Key == Key.Z && p2.Parent != workingAreaCanvas)
    {
        workingAreaCanvas.Children.Add(p2);
    }
}

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