Transparency with tga images

[Chiran]

I have a problem with making transparency work with tga images. What I have is a control with tga background image displayed on top of a window. The window background is 10% transparent so I'd like that the rounded corners of the tga image blend with the window background. At the moment I'm using 100% black corners which isn't too bad, but it isn't optimal.

I've toyed with the tga alpha channel (making corners black and such) and all the different blending modes but so far I haven't found a combination that would work the way I want. What usually happens is that the corners 'burn' a hole through the window, the image disappears completely, or the whole image burns a hole through the window.

Has anyone else encountered this problem and managed to make it work?

-Chiran