画矩形

xieyuan0553

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs;

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormMouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure FormMouseUp(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X,
      Y: Integer);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
var
    cx,cy:Integer;
    md:Boolean;
procedure TForm1.FormCreate(Sender: TObject);
begin
    Form1.DoubleBuffered:=True;
end;

procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
    md:=True;
    cx:=x;
    cy:=y;
end;

procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
    md:=False;
end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
    if md then
    begin
        Form1.Canvas.Rectangle(cx,cy,X,Y);
    end;
end;

end.

画矩形的代码是这样的，但当你把矩形拉大的时候再缩小，原来矩形就会留下痕迹。如何消除之前的矩形，不发生重叠？

aminghanhua

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
 if md then
    begin
    form1.Canvas.FillRect(Form1.ClientRect);//清除残影
    Form1.Canvas.Rectangle(cx,cy,X,Y);
    end;
end;