title: SnapsToDevicePixels issue
body: <p>In my WPF app, I have created few Line elements and added inside a StackPanel. The thickness for all lines is set to 0.5. But when I render it, sometimes few lines are appearing blur. I tried setting SnapsToDevicePixels in the StackPanel but this makes the lines completely invisible. Now if I increase the line thickness to 1 or greater than 1 then SnapsToDevicePixels is working properly. </p>
  
  <p>I am creating Line as shown below:</p>
  
  <pre><code>private void CreateLine(Double y1, Double y2, Double x1, Double x2, Double width, Double height)
  {
      Line line = new Line() { Y1 = y1, Y2 = y2, X1 = x1, X2 = x2, Width = width, Height = height };
  }
  </code></pre>
  
  <p>Here, if LineThickness is set to 0.5, x1 and x2 values will be 0.25 (LineThickenss / 2) and width is 0.5 (LineThickness).</p>
  
  <p>Is there any minimum pixel value required to be set in order to make the SnapsToDevicePixels work in WPF?</p>