Adding a transparent bitmap to a windows button

Question

It's a while since I've done this, but I'm trying to add a custom button graphic to a windows button, with some transparent areas. I've tried various schemes but can't seem to get the transparent areas to show. Here's my code:

hbmpUpDisabled = LoadImage(instance,MAKEINTRESOURCE(IDB_UPARROWDISABLED), IMAGE_BITMAP, 0, 0, LR_DEFAULTSIZE | LR_LOADTRANSPARENT | LR_LOADMAP3DCOLORS );

SendMessage(GetDlgItem(hWndDlg, IDC_MOVEUP),BM_SETIMAGE,(WPARAM)IMAGE_BITMAP,(LPARAM)hbmpUpDisabled);

Does anyone notice any problems here? It works if my bitmap is a 1-bit bitmap. I couldn't get a 32 bit bitmap to work, and I'm not sure how to setup a 24 bit or 8 bit bitmap to do it.... I tried a custom 255,0,255 color (which IIRC is a default transparent value), but so far no joy....

Answer 1

LR_LOADMAP3DCOLORS should map grey - in the source image - to to the current button face color. Buttons do not use AlphaBlt or TransparentBlt so there is no way to actually (short of custom painting) set a bitmap with transparent or alpha'd areas onto a button and expect it to work. You just have to pre-prepare the bitmap with the correct button color in its background areas.

• That said - I suspect that some of these restrictions may be lifted for buttons implemented by common controls v6. Add commctl 6 as a dependend assembly to your exe and see if the behaviour changes.