Draw a rectangle on a C # form

First on

Three mouse events

Private voidForm1_mousedown (Objectsender, MouseEventArgs e) {            //Record start point             This. MouseDown =true;  This. StartPoint =e.location; }        Private voidForm1_mousemove (Objectsender, MouseEventArgs e) {            //record the end point. Drawing to the window            if(MouseDown) { This. Endpoint =e.location;  This.                Refresh (); Gform. DrawImage ( This. Bmsave,NewPoint (0,0)); Rectangle rect=NewRectangle ();  This. Rect_play (refrect); Gform. DrawRectangle (NewPen (Color.Black), rect); }        }        Private voidForm1_mouseup (Objectsender, MouseEventArgs e) {            //record the end point. Draw to bitmap             This. Endpoint =e.location;  This. MouseDown =false; Rectangle rect=NewRectangle ();  This. Rect_play (refrect); G.drawrectangle (NewPen (Color.Black), rect); Gform. DrawImage ( This. Bmsave,NewPoint (0,0)); }

Determine the rectangle location and width,heigth to draw according to StartPoint and endpoint two points

        Private voidRect_play (refRectangle Rect) {            //determines the upper-left corner of the rectangle based on two points location            if( This. StartPoint. X > This. Endpoint. X && This. StartPoint. Y < This. Endpoint. Y) {rect. Location=NewPoint ( This. Endpoint. X This. StartPoint.            Y); }            Else if( This. StartPoint. X < This. Endpoint. X && This. StartPoint. Y > This. Endpoint. Y) {rect. Location=NewPoint ( This. StartPoint. X This. Endpoint.            Y); }            Else if( This. StartPoint. X > This. Endpoint. X && This. StartPoint. Y > This. Endpoint. Y) {rect. Location= This. Endpoint; }            Else{rect. Location= This. StartPoint; }            //get the X, y distance of two pointsRect. Width = Math.Abs ( This. StartPoint. X This. Endpoint.            X); Rect. Height= Math.Abs ( This. StartPoint. Y This. Endpoint.                        Y); if(Rect. Width = =0&& rect. Height = =0)            {                //prevent the drawing when it is delayed            }            Else if(Rect. Width = =0) {rect. Width=1; }            Else if(Rect. Height = =0) {rect. Height=1; }        }

Full instance Code link: Http://pan.baidu.com/s/1sjkpic1

The window flash when the painting is particularly powerful, because a lot of refresh and draw, open double buffering does not play much role

Late Time with QT C + + to do one, QT written should not blink

Draw a rectangle on a C # form