I am displaying a dialog as a layered window using code like this:
SetLayeredWindowAttributes(modalDlg, 0, 179, LWA_ALPHA);
...and everything works nicely on 32 bit Windows. However in WOW64 this results in every pixel either appearing black, or not appearing at all (zero transparency), depending on which PC we use.
We have four test machines for 64 bit Windows, two with NVidia and two with Intel video hardware, all running Win7 and we have tried the latest video drivers from each vendor and also the automatic update handled by Win7 (probably the same driver anyway...)
Unfortunately the question is muddied by the fact that ONE of these (NVidia) actually does display the transparent pixels as expected, which makes me a doubtful that this really is a problem with WOW64 rather than video drivers, but so far every machine that shows these symptoms is 64 bit.
If it makes any difference the dialog is shown over a fullscreen window playing video, controlled by MCI commands. I am also using SetLayeredWindowAttributes with the LWA_COLORKEY option for another dialog displayed over this video, but there are no problems with that one.
Any ideas...?
