鼠标画矩形

丿Clover灬夢

1. procedure TfrmCanvas.imgImageMouseDown(Sender: TObject;
   
2.   Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
   
3. begin
   
4.   with imgImage do
   
5.   begin
   
6.     oldx := x;
   
7.     oldy := y;
   
8.     Canvas.Brush.Style := bsClear;//画刷填充方式
   
9.     Canvas.Pen.Style := psDot; //线条类型
   
10.     Canvas.Pen.Mode := pmXor;
    
11.     Canvas.Pen.Color := clRed;
    
12.     rold := Rect(0, 0, 0, 0); //创建一个矩形对象
    
13.   end;
    
14. 
    
15.   if ssright in Shift then
    
16.   begin
    
17.    imgImage.Picture.Bitmap := nil;
    
18.   end;
    
19. end;
    
20. 
    
21. procedure TfrmCanvas.imgImageMouseMove(Sender: TObject; Shift: TShiftState;
    
22.   X, Y: Integer);
    
23. begin
    
24.   if not (ssleft in Shift) then Exit;
    
25.   with imgImage do
    
26.   begin
    
27.     Canvas.Rectangle(rold);//Rectangle根据提供的两个点或一个矩形区域绘制一个矩形
    
28.     Canvas.Rectangle(oldx, oldy, x, y);
    
29.     rold := Rect(oldx, oldy, x, y);
    
30.   end;
    
31. end;
    
32. 
    
33. procedure TfrmCanvas.imgImageMouseUp(Sender: TObject; Button: TMouseButton;
    
34.   Shift: TShiftState; X, Y: Integer);
    
35. begin
    
36.   with imgImage do
    
37.   begin
    
38.     Canvas.Pen.Style := psSolid;
    
39.     Canvas.Pen.Mode := pmCopy;
    
40.     Canvas.Pen.Color := clRed;
    
41.     Canvas.Rectangle(rold);
    
42.   end;
    
43. end;

复制代码

问题是在MouseMove事件中    Canvas.Rectangle(rold);//Rectangle根据提供的两个点或一个矩形区域绘制一个矩形
   Canvas.Rectangle(oldx, oldy, x, y);
    rold := Rect(oldx, oldy, x, y);
主要是实现了什么，求告知。。。谢谢！！！