请问:在使用Bitblt()时,如何使背景色透明?

Question

我有一幅图的背景是白色的，我想用BitBlt()将它帖到另一幅图上，并使它的白色背景透明，如何做呢？谢谢。

Answer 1

var
  b1, b2: TBitmap;
begin
  b1 := TBitmap.create;
  b2 := TBitmap.create;
  b1.loadfromfile('d:\1.bmp');
  b2.loadfromfile('d:\2.bmp');
  b2.Transparent := true;
  b2.TransparentColor := clWhite;  // 或 b2.canvas.pixels[0, 0];等
  b1.canvas.Draw(0, 0, b2);
  canvas.Draw(0, 0, b1);
  b1.free;
  b2.free;
end;

Answer 2

unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  ExtCtrls, StdCtrls;type
  TForm1 = class(TForm)
    Image1: TImage;
    Image2: TImage;
    Button1: TButton;
    Image3: TImage;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
  Form1: TForm1;
  b1,b2,b3,b4,b5,b6:tbitmap;
  trcolor:tcolor;
  oldcol:longint;
implementation{$R *.DFM}procedure TForm1.FormCreate(Sender: TObject);
begin
  trcolor:=clwhite;
  b1:=Tbitmap.Create;
  b2:=Tbitmap.Create;
  b3:=Tbitmap.Create;
  b4:=Tbitmap.Create;
  b5:=Tbitmap.Create;
  b6:=Tbitmap.Create;
  b1:=image1.Picture.Bitmap;
  b2:=image2.Picture.Bitmap;
  b3.Width:=b1.Width;
  b3.Height:=b1.Height;
  b3.Monochrome:=true;
  b4.Width:=b1.Width;
  b4.Height:=b1.Height;
  b4.Monochrome:=true;
  b5.Width:=b1.Width;
  b5.Height:=b1.Height;
  b6.Width:=b1.Width;
  b6.Height:=b1.Height;
end;procedure TForm1.Button1Click(Sender: TObject);
begin
  oldcol:=setbkcolor(b2.Canvas.Handle,colortorgb(trcolor));
  bitblt(b3.Canvas.Handle,0,0,b3.Width,b3.Height,b2.Canvas.Handle,0,0,srccopy);
  setbkcolor(b2.Canvas.Handle,oldcol);
  bitblt(b4.Canvas.Handle,0,0,b4.Width,b4.Height,b3.Canvas.Handle,0,0,notsrccopy);
  bitblt(b5.Canvas.Handle,0,0,b5.Width,b5.Height,b2.Canvas.Handle,0,0,srccopy);
  bitblt(b5.Canvas.Handle,0,0,b5.Width,b5.Height,b4.Canvas.Handle,0,0,srcand);
  bitblt(b6.Canvas.Handle,0,0,b6.Width,b6.Height,b1.Canvas.Handle,0,0,srccopy);
  bitblt(b6.Canvas.Handle,0,0,b6.Width,b6.Height,b3.Canvas.Handle,0,0,srcand);
  bitblt(b6.Canvas.Handle,0,0,b6.Width,b6.Height,b5.Canvas.Handle,0,0,srcinvert);
  image3.Picture.Bitmap:=b6;
  image3.Refresh;
end;procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
b1.Free;
b2.Free;
b3.Free;
b4.Free;
b5.Free;
b6.Free;
end;end.