做完这些准备工作后，将到了主要的部分，就是给控件画边框。
整个边框分为三个部分：四边框（用来设置可视区域与区域）+四条虚线（只用来显示）+八个小圆圈（用来斜角拖拉）。
所以要建立三个字段，用来分别保存这个数据。
Rectangle[] smallRects = new Rectangle[8];//边框中的八个小圆圈
Rectangle[] sideRects = new Rectangle[4];//四条边框，用来做响应区域
Point[] linePoints = new Point[5];//四条边，用于画虚线
接着就是创建用户控件的可视区域，和上面的三个变量数值。
（以下计算位置的代码，有兴趣的人可以研究下，没有的就直接Copy）
创建边框
#region 创建边框
/// <summary>
/// 建立控件可视区域
/// </summary>
private void CreateBounds()
{
//创建边界
int X = baseControl.Bounds.X - square.Width - 1;
int Y = baseControl.Bounds.Y - square.Height - 1;
int Height = baseControl.Bounds.Height + (square.Height * 2) + 2;
int Width = baseControl.Bounds.Width + (square.Width * 2) + 2;
this.Bounds = new Rectangle(X, Y, Width, Height);
this.BringToFront();
SetRectangles();
//设置可视区域
this.Region = new Region(BuildFrame());
g = this.CreateGraphics();
}
/// <summary>
/// 设置定义8个小矩形的范围
/// </summary>
void SetRectangles()
{
//左上
smallRects[0] = new Rectangle(new Point(0, 0), square);
//右上
smallRects[1] = new Rectangle(new Point(this.Width - square.Width - 1, 0), square);
//左下
smallRects[2] = new Rectangle(new Point(0, this.Height - square.Height - 1), square);
//右下
smallRects[3] = new Rectangle(new Point(this.Width - square.Width - 1, this.Height - square.Height - 1), square);
//上中
smallRects[4] = new Rectangle(new Point(this.Width / 2 - 1, 0), square);
//下中
smallRects[5] = new Rectangle(new Point(this.Width / 2 - 1, this.Height - square.Height - 1), square);
//左中
smallRects[6] = new Rectangle(new Point(0, this.Height / 2 - 1), square);
//右中
smallRects[7] = new Rectangle(new Point(square.Width + baseControl.Width + 1, this.Height / 2 - 1), square);
//四条边线
//左上
linePoints[0] = new Point(square.Width / 2, square.Height / 2);
//右上
linePoints[1] = new Point(this.Width - square.Width / 2 - 1, square.Height / 2);
//右下
linePoints[2] = new Point(this.Width - square.Width / 2 - 1, this.Height - square.Height / 2);
//左下
linePoints[3] = new Point(square.Width / 2, this.Height - square.Height / 2 - 1);
//左上
linePoints[4] = new Point(square.Width / 2, square.Height / 2);
//整个包括周围边框的范围
ControlRect = new Rectangle(new Point(0, 0), this.Bounds.Size);
}
/// <summary>
/// 设置边框控件可视区域
/// </summary>
/// <returns></returns>
private GraphicsPath BuildFrame()
{
GraphicsPath path = new GraphicsPath();
//上边框
sideRects[0] = new Rectangle(0, 0, this.Width - square.Width - 1, square.Height + 1);
//左边框
sideRects[1] = new Rectangle(0, square.Height + 1, square.Width + 1, this.Height - square.Height - 1);
//下边框
sideRects[2] = new Rectangle(square.Width + 1, this.Height - square.Height - 1, this.Width - square.Width - 1, square.Height + 1);
//右边框
sideRects[3] = new Rectangle(this.Width - square.Width - 1, 0, square.Width + 1, this.Height - square.Height - 1);
path.AddRectangle(sideRects[0]);
path.AddRectangle(sideRects[1]);
path.AddRectangle(sideRects[2]);
path.AddRectangle(sideRects[3]);
return path;
}
#endregion
