1、声明：

private Point mouseOffset; //记录鼠标指针的坐标
private bool isMouseDown = false; //记录鼠标按键是否按下

2、调用：

BLL.BitmapRegion.CreateControlRegion(this, new Bitmap(Application.StartupPath + "\pic\login.bmp"));

3、相关方法：

#region MouseDown事件
private void form1_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
{
     int xOffset;
     int yOffset;

     if (e.Button == MouseButtons.Left) 
     {
  xOffset = -e.X;// -SystemInformation.FrameBorderSize.Width;
  yOffset = -e.Y;// -SystemInformation.FrameBorderSize.Height;
  mouseOffset = new Point(xOffset, yOffset);
  isMouseDown = true;        
     }
 }
 #endregion

 #region MouseMove事件
 private void form1_MouseMove(object sender, System.Windows.Forms.MouseEventArgs e)
 {
     if (isMouseDown) 
     {
  Point mousePos = Control.MousePosition;
  mousePos.Offset(mouseOffset.X, mouseOffset.Y);
  Location = mousePos;
     }
 }
 #endregion

 #region MouseUp事件
 private void form1_MouseUp(object sender, System.Windows.Forms.MouseEventArgs e)
 {
     // 修改鼠标状态isMouseDown的值
     // 确保只有鼠标左键按下并移动时，才移动窗体
     if (e.Button == MouseButtons.Left)
     {
  isMouseDown = false;
     }
 }
 #endregion

4、实现代码如下：

using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Windows.Forms;

namespace BLL
{
    /// 
    /// Summary description for BitmapRegion. 
    ///  
    public class BitmapRegion
    {
 public BitmapRegion()
 { }

 ///  
 /// Create and apply the region on the supplied control
 /// 创建支持位图区域的控件（目前有button和form）
 ///  
 /// The Control object to apply the region to控件 
 /// The Bitmap object to create the region from位图 
 public static void CreateControlRegion(Control control, Bitmap bitmap)
 {
     // Return if control and bitmap are null
     //判断是否存在控件和位图
     if (control == null || bitmap == null)
  return;

     // Set our control''s size to be the same as the bitmap
     //设置控件大小为位图大小
     control.Width = bitmap.Width;
     control.Height = bitmap.Height;
     // Check if we are dealing with Form here 
     //当控件是form时
     if (control is System.Windows.Forms.Form)
     {
  // Cast to a Form object
  //强制转换为FORM
  Form form = (Form)control;
  // Set our form''s size to be a little larger that the  bitmap just 
  // in case the form''s border style is not set to none in the first place 
  //当FORM的边界FormBorderStyle不为NONE时，应将FORM的大小设置成比位图大小稍大一点
  form.Width = control.Width;
  form.Height = control.Height;
  // No border 
  //没有边界
  form.FormBorderStyle = FormBorderStyle.None;
  // Set bitmap as the background image 
  //将位图设置成窗体背景图片
  form.BackgroundImage = bitmap;
  // Calculate the graphics path based on the bitmap supplied 
  //计算位图中不透明部分的边界
  GraphicsPath graphicsPath = CalculateControlGraphicsPath(bitmap);
  // Apply new region 
  //应用新的区域
  form.Region = new Region(graphicsPath);
     }
     // Check if we are dealing with Button here 
     //当控件是button时
     else if (control is System.Windows.Forms.Button)
     {
  // Cast to a button object 
  //强制转换为 button
  Button button = (Button)control;
  // Do not show button text 
  //不显示button text
  button.Text = "";

  // Change cursor to hand when over button 
  //改变 cursor的style
  button.Cursor = Cursors.Hand;
  // Set background image of button 
  //设置button的背景图片
  button.BackgroundImage = bitmap;

  // Calculate the graphics path based on the bitmap supplied 
  //计算位图中不透明部分的边界
  GraphicsPath graphicsPath = CalculateControlGraphicsPath(bitmap);
  // Apply new region 
  //应用新的区域
  button.Region = new Region(graphicsPath);
     }
 }
 ///  
 /// Calculate the graphics path that representing the figure in the bitmap 
 /// excluding the transparent color which is the top left pixel. 
 /// //计算位图中不透明部分的边界
 ///  
 /// The Bitmap object to calculate our graphics path from 
 /// Calculated graphics path 
 private static GraphicsPath CalculateControlGraphicsPath(Bitmap bitmap)
 {
     // Create GraphicsPath for our bitmap calculation 
     //创建 GraphicsPath
     GraphicsPath graphicsPath = new GraphicsPath();
     // Use the top left pixel as our transparent color 
     //使用左上角的一点的颜色作为我们透明色
     Color colorTransparent = bitmap.GetPixel(0, 0);
     // This is to store the column value where an opaque pixel is first found. 
     // This value will determine where we start scanning for trailing opaque pixels.
     //第一个找到点的X
     int colOpaquePixel = 0;
     // Go through all rows (Y axis) 
     // 偏历所有行（Y方向）
     for (int row = 0; row < bitmap.Height; row++)
     {
  // Reset value 
  //重设
  colOpaquePixel = 0;
  // Go through all columns (X axis) 
  //偏历所有列（X方向）
  for (int col = 0; col < bitmap.Width; col++)
  {
      // If this is an opaque pixel, mark it and search for anymore trailing behind 
      //如果是不需要透明处理的点则标记，然后继续偏历
      if (bitmap.GetPixel(col, row) != colorTransparent)
      {
   // Opaque pixel found, mark current position
   //记录当前
   colOpaquePixel = col;
   // Create another variable to set the current pixel position 
   //建立新变量来记录当前点
   int colNext = col;
   // Starting from current found opaque pixel, search for anymore opaque pixels 
   // trailing behind, until a transparent   pixel is found or minimum width is reached 
   ///从找到的不透明点开始，继续寻找不透明点,一直到找到或则达到图片宽度 
   for (colNext = colOpaquePixel; colNext < bitmap.Width; colNext++)
       if (bitmap.GetPixel(colNext, row) == colorTransparent)
    break;
   // Form a rectangle for line of opaque   pixels found and add it to our graphics path 
   //将不透明点加到graphics path
   graphicsPath.AddRectangle(new Rectangle(colOpaquePixel, row, colNext - colOpaquePixel, 1));
   // No need to scan the line of opaque pixels just found 
   col = colNext;
      }
  }
     }
     // Return calculated graphics path 
     return graphicsPath;
 }
    }
}

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