procedure StretchBitmapTransparent(Dest: TCanvas; Bitmap: TBitmap;
  TransparentColor: TColor; DstX, DstY, DstW, DstH, SrcX, SrcY,
  SrcW, SrcH: Integer);
var
  CanvasChanging: TNotifyEvent;
begin
  if DstW <=  0  then DstW := Bitmap.Width;
  if DstH <=  0  then DstH := Bitmap.Height;
  if (SrcW <=  0 ) or (SrcH <=  0 ) then begin
    SrcX :=  0 ; SrcY :=  0 ;
    SrcW := Bitmap.Width;
    SrcH := Bitmap.Height;
  end;
  if not Bitmap.Monochrome then
    SetStretchBltMode(Dest.Handle, STRETCH_DELETESCANS);
  CanvasChanging := Bitmap.Canvas.OnChanging;
  try
    Bitmap.Canvas.OnChanging := nil;
    if TransparentColor = clNone then begin
      StretchBlt(Dest.Handle, DstX, DstY, DstW, DstH, Bitmap.Canvas.Handle,
        SrcX, SrcY, SrcW, SrcH, Dest.CopyMode);
    end
    else begin
      if Bitmap.Monochrome then TransparentColor := clWhite
      else TransparentColor := ColorToRGB(TransparentColor);
      StretchBltTransparent(Dest.Handle, DstX, DstY, DstW, DstH,
        Bitmap.Canvas.Handle, SrcX, SrcY, SrcW, SrcH, Bitmap.Palette,
        TransparentColor);
    end;
  finally
    Bitmap.Canvas.OnChanging := CanvasChanging;
  end;
end;

procedure DrawBitmapTransparent(Dest: TCanvas; DstX, DstY: Integer;
  Bitmap: TBitmap; TransparentColor: TColor);
begin
  StretchBitmapTransparent(Dest, Bitmap, TransparentColor, DstX, DstY,
    Bitmap.Width, Bitmap.Height,  0 ,  0 , Bitmap.Width, Bitmap.Height);
end;