From: "Henrik Palmér" <henrik.palmer@swipnet.se>
Newsgroups: borland.public.delphi.graphics
References: <3ac8ec1a_2@dnews>
Subject: SV: Maskblt - proper way
Date: Tue, 3 Apr 2001 21:31:54 +0200
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A better solution, compatible with Win9x, would be to call BitBlt twice:

procedure MaskBltC(Dest: HDC; ABitmap: TBitmap; TransparentColor: TColor; X,
Y: Integer);
  var
    Bitmap, Mask: TBitmap;
begin
  Bitmap := TBitmap.Create;
  Mask := TBitmap.Create;
  try
    Bitmap.Assign(ABitmap);
    Mask.Assign(ABitmap);
    Mask.Mask(TransparentColor);
    if TransparentColor <> clBlack then begin
      BitBlt(Mask.Canvas.Handle, 0, 0, Mask.Width, Mask.Height, 0, 0, 0,
DSTINVERT);
      BitBlt(Bitmap.Canvas.Handle, 0, 0, Bitmap.Width, Bitmap.Height,
Mask.Canvas.Handle, 0, 0, SRCAND);
      BitBlt(Mask.Canvas.Handle, 0, 0, Mask.Width, Mask.Height, 0, 0, 0,
DSTINVERT);
    end;
    BitBlt(Dest, X, Y, Mask.Width, Mask.Height, Mask.Canvas.Handle, 0, 0,
SRCAND);
    BitBlt(Dest, X, Y, Bitmap.Width, Bitmap.Height, Bitmap.Canvas.Handle, 0,
0, SRCPAINT);
  finally
    Bitmap.Free;
    Mask.Free;
  end;
end;


"Shannon Broskie" <shannonbroskie@tagfolio.com> skrev i meddelandet
news:3ac8ec1a_2@dnews...
> What is the proper way to transparently draw a bitmap?
>
> I need to use Maskblt because the final image will wind up being in the
> form's title bar.
>
> I'm having trouble generating the mask...
> Here's some code I've been using to play around with it...
>
> var
>   DC : HDC;
> begin
>   image1.Picture.Bitmap.Assign (imgLock.Picture.Bitmap);
>   image1.Picture.Bitmap.Mask (imgLock.Picture.Bitmap.TransparentColor);
>   DC := GetWindowDC (Self.Handle);
>   MaskBlt (DC, 100, 100, imgLock.Width, imgLock.Height,
> imgLock.Canvas.Handle, 0, 0,
>            image1.Canvas.Handle, 0, 0, SRCCOPY);
>
>
> The mask method of image1 seems to generate a mask that maskblt does not
> like...  Any ideas?
>
> Thanks in advance...