aliasing problem

Question

hello,

the code below draws two vertical lines on a canvas. these lines appear to be of different thickness on the screen although they are the same in code. i am tying to find a way to make them look as sharp as the border around the canvas. setting Path.SnapsToDevicePixels does not have any effect. The code is a contrived example, and in general the canvas that plots these lines can be nested deeper inside the visual tree.

thanks for any help konstantin

<Window x:Class="wpfapp.MyWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
  <Grid>
    <Border BorderBrush="Black"
            BorderThickness="1"
            Margin="10">
      <Canvas x:Name="Canvas"
              SizeChanged="OnCanvasSizeChanged" />
    </Border>
  </Grid>
</Window>

using System.Windows;
using System.Windows.Media;
using System.Windows.Shapes;

namespace wpfapp
{
    public partial class MyWindow : Window
    {
        public MyWindow()
        {
            InitializeComponent();
        }

        private void OnCanvasSizeChanged(object sender, SizeChangedEventArgs e)
        {
            StreamGeometry g = new StreamGeometry();
            double h = this.Canvas.ActualHeight;

            using (StreamGeometryContext c = g.Open())
            {
                c.BeginFigure(new Point(7, 0), false, false);
                c.LineTo(new Point(7, h), true, false);

                c.BeginFigure(new Point(14, 0), false, false);
                c.LineTo(new Point(14, h), true, false);
            }
            g.Freeze();

            Path p = new Path();

            p.Data = g;
            p.SnapsToDevicePixels = true;
            p.Stroke = new SolidColorBrush(Colors.Black);
            p.StrokeThickness = 1;

            this.Canvas.Children.Clear();
            this.Canvas.Children.Add(p);
        }
    }
}

Answer 1

Try adding

RenderOptions.EdgeMode="Aliased"

or in code behind

RenderOptions.SetEdgeMode(p, EdgeMode.Aliased);

UPDATE

The problem is SnapsToDevicePixels in combination with EdgeMode.Aliased. Remove SnapsToDevicePixels=true and keep EdgeMode.Aliased and you will get crisp 1px vertical lines

Answer 2

need to use GuidelineSet:

        protected override void OnRender(DrawingContext c)
        {
            base.OnRender(c);

            Pen pen = new Pen(Brushes.Black, 1);
            double h = this.ActualHeight;
            double d = pen.Thickness / 2;

            foreach (double x in new double[] { 7, 14 })
            {
                GuidelineSet g = new GuidelineSet(new double[] { x + d },
                                                  new double[] { 0 + d, h + d });

                c.PushGuidelineSet(g);
                c.DrawLine(pen, new Point(x, 0), new Point(x, h));
                c.Pop();
            }
        }