Transparent window containing opaque text and butt

Question

I'm creating a non-intrusive popup window to notify the user when processing a time-consuming operation. At the moment I'm setting its transparency by calling SetLayeredWindowAttributes which gives me a reasonable result:

alt text http://img6.imageshack.us/img6/3144/transparentn.jpg

However I'd like the text and close button to appear opaque (it doesn't quite look right with white text) while keeping the background transparent - is there a way of doing this?

Answer 1

In order to do "proper" alpha in a layered window you need to supply the window manager with a PARGB bitmap by a call to UpdateLayeredWindow.

The cleanest way to achieve this that I know of is the following:

1. Create a GDI+ Bitmap object with the PixelFormat32bppPARGB pixel format.
2. Create a Graphics object to draw in this Bitmap object.
3. Do all your drawing into this object using GDI+.
4. Destroy the Graphics object created in step 2.
5. Call the GetHBITMAP method on the Bitmap object to get a Windows HBITMAP.
6. Destroy the Bitmap object.
7. Create a memory DC using CreateCompatibleDC and select the HBITMAP from step 5 into it.
8. Call UpdateLayeredWindow using the memory DC as a source.
9. Select previous bitmap and delete the memory DC.
10. Destroy the HBITMAP created in step 5.

This method should allow you to control the alpha channel of everything that is drawn: transparent for the background, opaque for the text and button.

Also, since you are going to be outputting text, I recommend that you call SystemParametersInfo to get the default antialiasing setting (SPI_GETFONTSMOOTHING), and then the SetTextRenderingHint on the Graphics object to set the antialiasing type to the same type that is configured by the user, for a nicer look.

Answer 2

I suspect you'll need two top level windows rather than one - one that has the alpha blend and a second that is display above the first with the opaque text and button but with a transparent background. To accomplish this with a single window you'll need to use the UpdateLayeredWindow API call, but using this will cause your buttons to not redraw when they are interacted with (hover highlights, focus etc.)

It is possible that if this application is for Vista only there is a new API call that you can use, but I do not believe it is available in XP or earlier.

Answer 3

I can't say for sure, you'll need to try it, but since everything is a window, you could try setting the layered attributes for your button to make it opaque.

As for the text, you may be able to put that in its own frame with a set background and foreground color, and modify its layered attributes to make the background color transparent...

But since these are child windows and not the top-level window, I really don't know that it'll work.