Years ago I asked a question on the GFA MailingList about the .Picture property of the Command Ocx. At design-time the button displays the bitmaps of an ImageList properly, but when the program was run the pictures were showed with a black background. I forgot about it for years, but recently I created a program with buttons (Command Ocx) with images and the problem reappeared.
The image assigned to the button was definitely a masked-bitmap, without the transparent color applied. The difference with all those years back ant the present time, is the amount of documentation and interpretation of the dissassembly of the GfaWin23.Ocx. I immediately started a debugsession to see what happened when a iml.ListImages(idx).Picture is assigned to a Command Ocx.
The session turned out surprisingly informative, neither the Command nor the ImageList Ocx contained a bug. I was thinking wrongly, I used the wrong ListImage method, I should have used iml.ListImages(idx).ExtractIcon.
To begin with, the ImageList control was assigned a bitmap. However the control stores the single images in two separate bitmaps, a mask bitmap and a masked bitmap (because I had set the ImageList.UseMaskColor property). The background color of the bitmap image was blacked out (which I specified using the ImageList.MaskColor property.) I then invoked the following command to give the button a picture, assuming this would provide the Command Ocx with the original image I put into the ImageList control:
cmd.Picture = ImageListToolbar.ListImages(61).PictureBut I assumed wrongly. The .Picture property of the ImageList returned the handle of the masked bitmap only. So, to give a Command Ocx a transparent image from a ImageList Ocx use the .ExtractIcon method.
cmd.Picture = ImageListToolbar.ListImages(61).ExtractIconThe Command.Picture = pict pseudo-implementation is (without error and IsNothing checks) as follows:
type = pict.get_Type
handle = pict.get_Handle
SendMessage(Command.hWnd, BM_SETIMAGE, (type=1? IMAGE_BITMAP: IMAGE_ICON), handle)
Giving the Command.Picture property a Picture object containing an icon will result in a transparent image in a Button control.
Post a Comment