Title: How to draw a transparent bitmap
Question:
Answer:
procedure DrawTransparentBmp(Cnv: TCanvas; x,y: Integer; Bmp: TBitmap;
clTransparent: TColor);
var
bmpXOR, bmpAND, bmpINVAND, bmpTarget: TBitmap;
oldcol: Longint;
begin
try
bmpAND := TBitmap.Create;
bmpAND.Width := Bmp.Width;
bmpAND.Height := Bmp.Height;
bmpAND.Monochrome := True;
oldcol := SetBkColor(Bmp.Canvas.Handle, ColorToRGB(clTransparent));
BitBlt(bmpAND.Canvas.Handle, 0,0,Bmp.Width,Bmp.Height, Bmp.Canvas.Handle,
0,0, SRCCOPY);
SetBkColor(Bmp.Canvas.Handle, oldcol);
bmpINVAND := TBitmap.Create;
bmpINVAND.Width := Bmp.Width;
bmpINVAND.Height := Bmp.Height;
bmpINVAND.Monochrome := True;
BitBlt(bmpINVAND.Canvas.Handle, 0,0,Bmp.Width,Bmp.Height,
bmpAND.Canvas.Handle, 0,0, NOTSRCCOPY);
bmpXOR := TBitmap.Create;
bmpXOR.Width := Bmp.Width;
bmpXOR.Height := Bmp.Height;
BitBlt(bmpXOR.Canvas.Handle, 0,0,Bmp.Width,Bmp.Height, Bmp.Canvas.Handle,
0,0, SRCCOPY);
BitBlt(bmpXOR.Canvas.Handle, 0,0,Bmp.Width,Bmp.Height,
bmpINVAND.Canvas.Handle, 0,0, SRCAND);
bmpTarget := TBitmap.Create;
bmpTarget.Width := Bmp.Width;
bmpTarget.Height := Bmp.Height;
BitBlt(bmpTarget.Canvas.Handle, 0,0,Bmp.Width,Bmp.Height, Cnv.Handle, x,y,
SRCCOPY);
BitBlt(bmpTarget.Canvas.Handle, 0,0,Bmp.Width,Bmp.Height,
bmpAND.Canvas.Handle, 0,0, SRCAND);
BitBlt(bmpTarget.Canvas.Handle, 0,0,Bmp.Width,Bmp.Height,
bmpXOR.Canvas.Handle, 0,0, SRCINVERT);
BitBlt(Cnv.Handle, x,y,Bmp.Width,Bmp.Height, bmpTarget.Canvas.Handle, 0,0,
SRCCOPY);
finally
bmpXOR.Free;
bmpAND.Free;
bmpINVAND.Free;
bmpTarget.Free;
end;
end;