Draw an image instead of window caption - delphi

Question

I need to do something which seems to be easy, but I'm searching for days with no success.
I have a window of fixed size (say 500*250) and need to replace the whole caption bar with a fixed size JPEG (or better PNG) image (say 500*25).
There are lots of samples talking about Glass, Aero, DWM, blah blah blah. But I just need to draw a fixed image!
I've already tried this, but it doesn't work:
procedure TForm1.Button1Click(Sender: TObject);
var
bmp:TBitmap;
DC:HDC;
begin
DC:=GetWindowDC(form1.Handle);
bmp:=tbitmap.Create;
bmp.SetSize(500, 25);
bmp.Canvas.TextOut(5,5,'Helloooooooooooooooooo');
BitBlt(dc,0,0,500,25,bmp.Canvas.Handle,0,0,SRCCOPY);
bmp.Free;
ReleaseDC(form1.Handle,DC);
end;
It should work both on XP and Vista/7. Please help.
P.S: I have Delphi XE.

Answer 1

You can do so by using VCL Styles.
You can change the appearance of the Windows caption bar like that by using the Delphi integrated Bitmap style designer to change a custom style and then use that Style in your application.
If you don't want to enforce the style to the whole application you can set the StyleElements property of the form to only include seBorder, this means that only the border aka caption of your application will be rendered using your custom style.
If you're working in Delphi XE2 then you won't be able to use the StyleElements property but that is just a minor obstacle, it just means that you will have to resort to using StyleHooks to implement the same behaviour and there is enough documentation on how to do that here.
Sadly, if your Delphi version is older then XE2 then you won't be able to use VCL Styles.
Another but rather unpleasant way would be to create a borderless form by changing the BorderStyle property to bsNone and then implementing your image in a way that it would act as a title bar, processing all actions made on the image and sending appropriate Messages to the application.

Answer 2

You can either:
Intercept the WM_NCPAINT message and custom-draw the caption bar manually.
Remove the caption bar altogether, by using SetWindowRgn() or overriding the CreateParams() method to remove the WS_CAPTION style, and then use the form's OnPaint event, or even a TImage, to display the graphic at the top of the form's remaining client area.
The simplest solution would be to use CreateParams() and TImage.