c# GDI 畫圓，可以調整大小等功能

問題情境：

　　上司對自己的關懷，稱現有的畫圈圈區域不太理想，需要有：

　　　　可拖拽移動圓的位置，

　　　　滾輪可以控制大小，

　　　　邊界也可以通過拖拽調整圓的長軸短軸調整大小。

原理描述：

　　1.畫形狀容易實現；

　　2.調整大小通過整個窗體的鼠標move事件。來進行實時刷新顯示；

　　3.拖拽移動位置用mousedown事件和MouseMove事件，可以實時監控光標位置；

　　4.滾輪控制用MouseWheel事件，MouseEventArgs的Delta屬性可控制上下滾；

自己做了個簡單demo實例：

　　

       public Form1()
        {
            InitializeComponent();

            this.MouseWheel += new System.Windows.Forms.MouseEventHandler(this_MouseWheel);
            this.MouseMove += new System.Windows.Forms.MouseEventHandler(this_MouseMove);
            this.MouseDown += new System.Windows.Forms.MouseEventHandler(this_MouseDown);

            DrawRect.X = (this.Width - DrawRect.Width) / 2;
            DrawRect.Y = (this.Height - DrawRect.Height) / 2;
            log("zoom        width        height");
        }

        //矩形框坐標
        private Rectangle DrawRect = new Rectangle(0, 0, 100, 100);
        //鼠標按下時坐標
        private Point MouseDownP = new Point();
        //放大倍數
        private int zoom = 0;
        //鼠標移動矩形框次數，如果移動過矩形框則不從中心放大，以移動后的位置放大縮小，縮小為原大小，縮放數為0時，重置此數
        private int MoveCount = 0;

        private void this_MouseWheel(object sender, MouseEventArgs e)
        {
            Rectangle tmpRec = DrawRect;
            int zmTemp = zoom;
            int incTemp = 0;
            if (e.Delta > 0)//上滾放大
            {
                if (zoom < 80)// 最大放大80倍             
                    zoom++;
                incTemp = -zoom;
            }
            else//下滾縮小
            {
                if (zoom > 0)
                    incTemp = zoom--;
                if (zoom == 0) //放大倍數＝0,不放大，鼠標拖動標記歸0      
                    MoveCount = 0;
                
            }
            //放大原理   
            //1、先獲取放大倍數  
            //2、根據放大倍數，計算矩形框高度，高度＝控件高度－倍數×2；  
            //3、根據高度，提取矩形寬度，寬度＝高度×（控件寬度/控件高度），為保證矩形和原控件縱橫比例，所以要乘以比例     
            //4、根據矩形框大小，和控件大小，計算矩形框在控件中的位置，即X,Y坐標           
            //1）如果沒有拖動過矩形，則按默認中間位置取值，X＝（控件寬度－矩形寬度)/2,Y＝（控件高度－矩形高度）/2      
            //2）如果拖動過矩形框，則原X，Y坐標不變化       
            //5、根據得到的新矩形框的坐標和范圍，判斷是否超界，判斷XY坐標
            //滾輪放大事件     
            //矩形區域高度=控件高度-放大縮小倍數*2
            double ratio = Math.Round(DrawRect.Width / (DrawRect.Height * 1.0) , 2);
            DrawRect.Height = DrawRect.Height - incTemp * 2;
            //按比例計算寬度   
            DrawRect.Width = (int)(Convert.ToSingle(DrawRect.Height) * ratio);
            //if (MoveCount == 0)//沒有拖動過，滾動滾輪才按中間放大縮小    
            //{
            //    DrawRect.X = (this.Width - DrawRect.Width) / 2;
            //    DrawRect.Y = (this.Height - DrawRect.Height) / 2;
            //}
            //===============判斷是否超界＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝         
            //如果Right超過控件寬度          
            if (DrawRect.Right > this.Width)
            {
                DrawRect = tmpRec;
                zoom = zmTemp;
                return;
            }
            //如果Bottom超過控件高度      
            if (DrawRect.Bottom > this.Height - 20)
            {
                DrawRect = tmpRec;
                zoom = zmTemp;
                return;
            }
            DrawImg();
        }

        int cursorFlag = 0;
        private void this_MouseMove(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                int limitRadius = 5;
                if (cursorFlag != 0)
                {
                    switch (cursorFlag)
                    {
                        case 1://left
                            if (DrawRect.Width + DrawRect.X - e.X < limitRadius)
                            {
                                return;
                            }
                            DrawRect.Width += DrawRect.X - e.X;
                            DrawRect.X = e.X;
                            break;
                        case 2://right
                            if (e.X - DrawRect.X < limitRadius)
                            {
                                return;
                            }
                            DrawRect.Width = e.X - DrawRect.X;
                            break;
                        case 3://top 
                            if (DrawRect.Height + DrawRect.Y - e.Y < limitRadius)
                            {
                                return;
                            }
                            DrawRect.Height += DrawRect.Y - e.Y;
                            DrawRect.Y = e.Y;
                            break;
                        case 4://bottom
                            if (e.Y - DrawRect.Y < limitRadius)
                            {
                                return;
                            }
                            DrawRect.Height = e.Y - DrawRect.Y;
                            break;
                    }
                    DrawImg();
                }
                else
                {
                    if (DrawRect.Contains(MouseDownP))//判斷鼠標按下的坐標是否在紅框中，確定是否拖動的紅框     
                    {
                        //拖動鼠標位置，矩形框新X＝矩形框原X＋（當前鼠標X－按下時X），原X＋偏移量        
                        //Y軸一樣變化
                        DrawRect.X = DrawRect.X + (e.X - MouseDownP.X); //.Location = ClienP;        
                        DrawRect.Y = DrawRect.Y + (e.Y - MouseDownP.Y); // ClienP.Y;
                                                                        //判斷是否超過左上角           
                        if (DrawRect.X < 0)
                            DrawRect.X = 0;
                        if (DrawRect.Y < 0)
                            DrawRect.Y = 0;
                        //判斷是否超過右下角     
                        if (DrawRect.X > (this.Width - DrawRect.Width - 1))
                            DrawRect.X = this.Width - DrawRect.Width - 1;
                        if (DrawRect.Y > (this.Height - DrawRect.Height - 1))
                            DrawRect.Y = this.Height - DrawRect.Height - 1;
                        //畫圖              
                        DrawImg();
                        //計算完坐標系，鼠標按下坐標轉換成當前鼠標坐標，以重新計算偏移           
                        MouseDownP.X = e.X;
                        MouseDownP.Y = e.Y;
                        //拖動過鼠標，鼠標拖動標記累加         
                        MoveCount++;
                    }
                }
            }
            else
            {
                //如果光標在邊界上，顯示對應的光標形狀
                int boundary = 3;
                if ((e.X <= DrawRect.X - 1 && e.X >= DrawRect.X - boundary)
                    && e.Y >= DrawRect.Y && e.Y <= DrawRect.Y + DrawRect.Height)//left
                {
                    cursorFlag = 1;
                    this.Cursor = Cursors.SizeWE;
                }
                else if ((e.X >= DrawRect.X + DrawRect.Width + 1 && e.X <= DrawRect.X + DrawRect.Width + boundary)
                    && e.Y >= DrawRect.Y && e.Y <= DrawRect.Y + DrawRect.Height)//right
                {
                    cursorFlag = 2;
                    this.Cursor = Cursors.SizeWE;
                }
                else if ((e.Y <= DrawRect.Y - 1 && e.Y >= DrawRect.Y - boundary)
                    && e.X > DrawRect.X && e.X < DrawRect.X + DrawRect.Width)//top
                {
                    cursorFlag = 3;
                    this.Cursor = Cursors.SizeNS;
                }
                else if ((e.Y >= DrawRect.Y + DrawRect.Height + 1 && e.Y <= DrawRect.Y + DrawRect.Height + boundary)
                    && e.X > DrawRect.X && e.X < DrawRect.X + DrawRect.Width)//bottom
                {
                    cursorFlag = 4;
                    this.Cursor = Cursors.SizeNS;
                }
                else
                {
                    cursorFlag = 0;
                    this.Cursor = Cursors.Default;
                }
            }
        }
        private void this_MouseDown(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
                MouseDownP = new Point(e.X, e.Y);
        }
        void DrawImg()
        {
            using (Graphics g = this.CreateGraphics())
            {
                //重繪背景 Ellipse Rectangle
                g.FillRectangle(new SolidBrush(Color.LightGray), 0, 0, this.Width, this.Height);//達到去重效果
                g.DrawString("滾輪放大，左鍵拖動矩形框" + zoom, new Font("黑體", 12f), new SolidBrush(Color.Green), 5, 5);
                g.DrawString("放大" + zoom, new Font("黑體", 12f), new SolidBrush(Color.Red), 5, 20);
                //重繪矩形
                g.DrawEllipse(new Pen(Color.Red), DrawRect);
                g.DrawRectangle(new Pen(Color.Red), DrawRect);
                //日志
                log(zoom.ToString("00") + "               " + DrawRect.Width + "          " + DrawRect.Height);
            }
        }

        private void log(string text)
        {
            string path = Application.StartupPath + "\\" + DateTime.Now.ToString("yyyy-MM-dd") + ".log";
            StreamWriter sw = File.AppendText(path);
            sw.WriteLine(text);
            sw.Flush();
            sw.Close();
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = this.CreateGraphics();
            //重繪背景 Ellipse Rectangle
            g.FillRectangle(new SolidBrush(Color.LightGray), 0, 0, this.Width, this.Height);//達到去重效果
            g.DrawString("滾輪放大，左鍵拖動矩形框" + zoom, new Font("黑體", 12f), new SolidBrush(Color.Green), 5, 5);
            g.DrawString("放大" + zoom, new Font("黑體", 12f), new SolidBrush(Color.Red), 5, 20);
            //重繪矩形
            DrawRect.X = (this.Width - DrawRect.Width) / 2;
            DrawRect.Y = (this.Height - DrawRect.Height) / 2;
            g.DrawEllipse(new Pen(Color.Red), DrawRect);
            g.DrawRectangle(new Pen(Color.Red), DrawRect);
        }