C# 绘图问题

Question

使用C# GDI+绘图中，如何实现以下效果？随着鼠标的移动画矩形线（及时删除原来的矩形框），松开鼠标时显示最后状态下的矩形框

Answer 1

把以前做的一个东西裁剪了一下，供参考
    public partial class Form1 : Form
    {
        private bool isDrawing = false;
        Rectangle currentShape;
        private BufferedGraphics bg;
        public Form1()
        {
            InitializeComponent();
        }        private void Form1_Load(object sender, EventArgs e)
        {
            this.BackColor = Color.White;
            bg = BufferedGraphicsManager.Current.Allocate(this.CreateGraphics(), this.ClientRectangle);        }
        private void Form1_MouseDown(object sender, MouseEventArgs e)
        {
            if (!isDrawing)
            {
                isDrawing = true;
                currentShape = new Rectangle(e.Location, 0, 0);
            }
        }        private void Form1_MouseUp(object sender, MouseEventArgs e)
        {
            if (isDrawing)
            {
                isDrawing = false;
                currentShape = null;
            }
        }        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            if (isDrawing)
            {
                Rectangle rectangle = (Rectangle)currentShape;
                rectangle.RectangleWidth = e.X - rectangle.Location.X;
                rectangle.RectangleHight = e.Y - rectangle.Location.Y;
                bg.Graphics.Clear(Color.White);
                rectangle.Draw(bg.Graphics);
                bg.Render();
            }        }
    }    class Rectangle
    {        private Point location;
        public Point Location
        {
            get { return location; }
            set { location = value; }
        }        private int rectangleHeight;        public int RectangleHight
        {
            get { return rectangleHeight; }
            set { rectangleHeight = value; }
        }
        private int rectangleWidth;        public int RectangleWidth
        {
            get { return rectangleWidth; }
            set { rectangleWidth = value; }
        }        public Rectangle(Point location, int rectangleWidth, int rectangleHeight)
        {
            this.location = location;
            this.rectangleWidth = rectangleWidth;
            this.rectangleHeight = rectangleHeight;
        }        public void Draw(Graphics gfx)
        {
            Point actualLocation = new Point(
                location.X + (rectangleWidth >= 0 ? 0 : rectangleWidth),
                location.Y + (rectangleHeight >= 0 ? 0 : rectangleHeight)
                );
            int actualWidth = (rectangleWidth >= 0 ? rectangleWidth : -rectangleWidth);
            int actualHeight = (rectangleHeight >= 0 ? rectangleHeight : -rectangleHeight);
            gfx.DrawRectangle(Pens.Red, actualLocation.X, actualLocation.Y, actualWidth, actualHeight);
        }
    }

Answer 2

用gdi的异或原理画图吧，这样容易擦除。
注意，不是gdi++

Answer 3

这是个DrawReversibleFrame的例子:public partial class Form1 : Form
{
    Point startPoint = new Point(-1, -1);
    Rectangle lastRect = Rectangle.Empty;
    List<Rectangle> rectangles = new List<Rectangle>();    public Form1()
    {
        InitializeComponent();
    }    protected override void OnMouseDown(MouseEventArgs e)
    {
        this.startPoint = this.PointToScreen(e.Location);
    }    protected override void OnMouseMove(MouseEventArgs e)
    {
        if (this.startPoint.X >= 0)
        {
            Point current = this.PointToScreen(e.Location);
            Size size = new Size(current.X - startPoint.X, current.Y - startPoint.Y);            ControlPaint.DrawReversibleFrame(lastRect, this.BackColor, FrameStyle.Dashed);  //擦旧
            lastRect = new Rectangle(startPoint, size);
            ControlPaint.DrawReversibleFrame(lastRect, this.BackColor, FrameStyle.Dashed);  //画新
        }
    }    protected override void OnMouseUp(MouseEventArgs e)
    {
        if (this.startPoint.X >= 0)
        {
            ControlPaint.DrawReversibleFrame(lastRect, this.BackColor, FrameStyle.Dashed);  //擦
            this.startPoint.X = -1;            this.rectangles.Add(Normalize(this.RectangleToClient(lastRect)));
            this.lastRect = Rectangle.Empty;
            this.Invalidate();
        }
    }    protected override void OnPaint(PaintEventArgs e)
    {
        foreach (Rectangle rect in this.rectangles)
        {
            e.Graphics.DrawRectangle(Pens.Black, rect);
        }
    }    private Rectangle Normalize(Rectangle rect)
    {
        if (rect.Width < 0) { rect.X += rect.Width; rect.Width = -rect.Width; }
        if (rect.Height < 0) { rect.Y += rect.Height; rect.Height = -rect.Height; }
        return rect;
    }
}

Answer 4

lz如果是这样移动一个图中的部分的话，建立lz最好不要这么搞...会出现闪烁...效果很差...
我以前也用GDI+做过流程图..

Answer 5

http://blog.csdn.net/null1/archive/2008/10/22/3124630.aspx