GDI+ Region Bug

Here is an interesting (and annoying) bug found in GDI+ : when doing the union of several regions (2 outlines and 2 surfaces), GDI+ produces an incorrect resulting region. The screenshot below shows the problem :

The region (in light green) is the result of doing the union of following regions :

1. The figure #1 (vertical rectangle) outline.
2. The figure #1 surface.
3. The figure #2 (horizontal rectangle) outline.
4. The figure #2 surface.

The right part of figure #2 is missing altogether in the resulting region !

Changing the order in which the basic regions get added changes the output.

You can download :

• The source code of the demonstration application.
• The .NET executable.