如果拖动鼠标在图片上画矩形？

Question

如果拖动鼠标在图片上画矩形？
按下鼠标左键开始画矩形，松开左键结束画矩形，矩形可以有背景颜色，并且可用用鼠标拖动矩形移动，可以拖动四个边框改变矩形大小。请问需要用到哪些GDI+的函数，特别是画矩形的过程中如何擦除原来的矩形！
请大家给个思路

Answer 1

话矩形http://www.farooqazam.net/draw-a-rectangle-in-c-sharp-using-mouse/

Answer 2

using System;
using System.Collections;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.Windows.Forms;
using PhotoSprite.ImageProcessing;namespace PhotoSprite.Tool
{
  /// <summary>
  /// 矩形工具类
  /// </summary>
  public class RectangleTool : Tool
  {
    private Canvas canvas = null;
    private Bitmap image = null;
    private Bitmap srcImage = null;
    private Graphics gImage;
    private Graphics gSurface;
    private bool mouseDown = false;
    private Point startPoint, lastPoint;
    private Pen pen = null;    /// <summary>
    /// 使用矩形工具
    /// </summary>
    /// <param name="parent">画布</param>
    public RectangleTool(Canvas parent)
    {
      this.canvas = parent;
      gSurface = canvas.CreateGraphics();
    }    public void OnActivate()
    {
      this.canvas.MouseDown += this.OnMouseDown;
      this.canvas.MouseMove += this.OnMouseMove;
      this.canvas.MouseUp += this.OnMouseUp;
    }    public void OnDeactivate()
    {
      this.canvas.MouseDown -= this.OnMouseDown;
      this.canvas.MouseMove -= this.OnMouseMove;
      this.canvas.MouseUp -= this.OnMouseUp;
    }    public void OnMouseDown(object sender, MouseEventArgs e)
    {
      if (((e.Button & MouseButtons.Left) == MouseButtons.Left) ||
        ((e.Button & MouseButtons.Right) == MouseButtons.Right))
      {
        mouseDown = true;
        lastPoint = startPoint = new Point(e.X, e.Y);        // 左键为前景颜色，右键为背景颜色
        if ((e.Button & MouseButtons.Left) == MouseButtons.Left)
        {
          pen = new Pen(new SolidBrush(this.ForeColor), this.BrushWidth);
        }
        else if ((e.Button & MouseButtons.Right) == MouseButtons.Right)
        {
          pen = new Pen(new SolidBrush(this.BackColor), this.BrushWidth);
        }        // 锁定画布图像
        this.image = this.canvas.Image;
        this.srcImage = (Bitmap)this.image.Clone();
        gImage = System.Drawing.Graphics.FromImage(image);
      }
    }    public void OnMouseMove(object sender, MouseEventArgs e)
    {
      if (mouseDown)
      {
        Point mouseXY = new Point(e.X, e.Y);
        mouseXY = Function.PointInRectangle(mouseXY, this.canvas.Bounds);
        if (mouseXY.X == this.canvas.Width - 1) mouseXY.X = this.canvas.Width - 2;
        if (mouseXY.Y == this.canvas.Height - 1) mouseXY.Y = this.canvas.Height - 2;
        
        // 消除上次痕迹
        Rectangle lastRect = Function.PointsToRectangle(startPoint, lastPoint);        
        Rectangle lastOutlineRect = lastRect;
        lastOutlineRect.Inflate(2, 2);
        Rectangle lastInteriorRect = lastRect;
        lastInteriorRect.Inflate(-2, -2);
        Region invalidRegion = new Region(lastOutlineRect);
        invalidRegion.Xor(lastInteriorRect);        this.canvas.Invalidate(invalidRegion);
        this.gImage.DrawImage((Bitmap)this.srcImage.Clone(), lastOutlineRect, lastOutlineRect, GraphicsUnit.Pixel);
        
        // 绘制表面
        Rectangle rect = Function.PointsToRectangle(startPoint, mouseXY);
        //this.gSurface.DrawRectangle(pen, rect);        // 绘制到图像
        this.gImage.DrawRectangle(pen, rect);        lastPoint = mouseXY;
      }
    }    public void OnMouseUp(object sender, MouseEventArgs e)
    {
      if (mouseDown)
      {
        Point mouseXY = new Point(e.X, e.Y);        // 绘制矩形
        Graphics g = Graphics.FromImage(this.srcImage);
        g.DrawRectangle(pen, Function.PointsToRectangle(startPoint, mouseXY));
        this.gImage.DrawImage((Bitmap)this.srcImage.Clone(), 0,0);        startPoint = Point.Empty;
        lastPoint = Point.Empty;
        mouseDown = false;        pen.Dispose();
        this.canvas.Invalidate();        // 触发绘图结束事件
        OnDrawingFinished();
      }
    }
    /// <summary>
    /// 在绘图结束时发生
    /// </summary>
    public event EventHandler DrawingFinished;
    protected void OnDrawingFinished()
    {
      if (DrawingFinished != null)
      {
        DrawingFinished(this, EventArgs.Empty);
      }
    }
  }
}