I am basically trying to achieve this effect:
...Where an area of the app is completely transparent (left side in that image), to the point where you can see the desktop (and other background windows behind it). The blur is not the difficult part. It's making the window transparent. I am just not able to make the window transparent (either as the entire window or a part of it). It just remains white.
Doing research on the undocumented SetWindowCompositionAttribute
API has not really helped much.
Here is a similar question, but it doesn't seem to be in C#: How do you set the glass blend colour on Windows 10?