WPF Tiled Background Misalignment

Question

We have quite a complex WPF application (that I cannot show here) that somehow has the tiled background misaligned of one of its user controls. I was unable to reproduce this problem in a "clean" WPF project but will try to illustrate the problem in this picture:

The gray area represents the user control and the black and red checks represents the tiled background inside the user control. The white background represents the window hosting the control. The VisualBrush is used here but the same problem comes with the DrawingBrush. I would prefer not to use the ImageBrush.

Can you open a "clean" WPF project and build something that will cause a tiled background to be misaligned like this?

Answer 1

You can do this if the layout root of the user control has a -10 left margin and a -10 top margin. the tiled backgoround in on the layout root of the usercontrol so, it looks like a alignment problem not a brush problem.

Answer 2

This problem is related to the tiled background cramming itself into the calculated height of the UserControl instance in the hosting Window. I am still unable to replicate this problem in a new project but it is "solved" (by stacking panels in the user control horizontally instead of vertically).

Answer 3

Here are two diagnostic techniques that can be useful in situations like yours:

1. Take your complex project, make a copy, and start tearing out large sections of code and XAML until the problem disappears. Then put the last section back and tear things out more gently. Repeat until you find the change that makes the difference.

2. Run the application, break where a local variable references your UserControl, then explore the visual tree just above and below your UserControl in the Locals or Watch window. Look at each Visual's internal properties VisualOffset, VisualTransform, and VisualContentBounds. These properties will usually clue you in to what property is being set incorrectly, and from there you can figure out why.

Answer 4

Check the DPI of the image. WPF defaults to 96 DPI.