I am playing around with a small MFC-wizard-generated application, in Visual C++ 2010, and I just decided to put my own bitmap into the resources to replace the three-cubes MFC bitmap that shows up in the ribbon UI Application Button, aka the “marble”.
The original appeared to use black (0,0,0) as a transparency color, but I am unable to determine what the MFC Ribbon (mfc-feature-pack stuff) stuff in Visual Studio 2010 does to determine transparency on a bitmap used as the ribbon’s main icon.
The properties of the ribbon (IDR_RIBBON) show Image=IDB_MAIN, and IDB_MAIN is a 32×32 bitmap in BMP format, loaded from a disk file called main.bmp.
Some of the bitmap resources in this project have what looks like what I would expect: A magenta color which becomes transparent, but the MFC main bitmap did not use this color scheme or palette.
Here is an example of the actual results, which are I hope show that the results are not what I wanted:
Incidentally, It does not seem possible to use an ICON resource in the Application Button, so I am a little mystified how they pull off the transparency in it.
Translucent PNG, perhaps? Did you know that BMP files can also have alpha channels?