SetWindowLong 给MDI窗体加背景

//给MDI窗体加背景 
//设置Form1窗体的FormStyle属性为fsMDIForm
//设置Form2窗体的FormStyle属性为fsMDIChild

// Image控件 Bmp格式图片

  private
      FClientInstance : TFarProc;
      FPrevClientProc : TFarProc;
      Procedure ClientWndProc(Var Message: TMessage);

procedure TForm1.ClientWndProc(var Message: TMessage);
var
      Dc : hDC;
      Row : Integer;
      Col : Integer;
begin
  with Message do
    case Msg of
    WM_ERASEBKGND://当要重会背景时
    begin
      Dc := TWMEraseBkGnd(Message).Dc;
      // 铺图象
      //计算并会制行和高总共要画的数量。
      for Row := 0 to ClientHeight div Image1.Picture.Height do
        for Col := 0 to ClientWidth div Image1.Picture.Width do
          BitBlt(Dc,Col * Image1.Picture.Width,Row * Image1.Picture.Height
                 ,Image1.Picture.Width,Image1.Picture.Height
                 ,Image1.Picture.Bitmap.Canvas.Handle,0,0,SRCCOPY);
      Result := 1;
      end;
    else // 传递其他消息
      Result := CallWindowProc(FPrevClientProc,ClientHandle,Msg,wParam,lParam);
  end;
end;
procedure TForm1.FormShow(Sender: TObject);
begin
  FClientInstance := MakeObjectInstance(ClientWndProc);//将自定义过程的地址入口存入PClientInstance中
  FPrevClientProc := Pointer(GetWindowLong(ClientHandle,GWL_WNDPROC));//记录消息位置
  SetWindowLong(ClientHandle,GWL_WNDPROC,LongInt(FClientInstance));//重新载入窗口的消息并继续处理。
end;

//为非MDI窗体制作背景

通过 Wiz 发布