如何对一个矩形进行旋转操作？

Question

使用Matrix的Rotate方法。        private void Form1_Paint(object sender, PaintEventArgs e)
        {
    Pen myPen = new Pen(Color.Blue, 1);
    Pen myPen2 = new Pen(Color.Red, 1);
             
    // Draw the rectangle to the screen before applying the transform.
    e.Graphics.DrawRectangle(myPen, 150, 50, 200, 100);
             
    // Create a matrix and rotate it 45 degrees.
    Matrix myMatrix = new Matrix();
    myMatrix.Rotate(45, MatrixOrder.Append);
             
    // Draw the rectangle to the screen again after applying the
             
    // transform.
    e.Graphics.Transform = myMatrix;
    e.Graphics.DrawRectangle(myPen2, 150, 50, 200, 100);
        }

Answer 1

//取得点p1围绕点p2顺时针旋转a度后的位置
private Point PRotate(Point p1,Point p2,double a)
{
double x1=(double)(p1.X-p2.X);
double y1=(double)(p2.Y-p1.Y);
double aa=Math.PI*a/180;
return new Point((int)(y1*Math.Sin(aa)+x1*Math.Cos(aa))+p2.X,p2.Y-(int)(y1*Math.Cos(aa)-x1*Math.Sin(aa)));
}
//画出矩形r1围绕点p旋转a度后的图形
private void DrawRotateRect(Rectangle r1,Point p,double a,Graphics g1,Pen pen)
{
Point p1=PRotate(new Point(r1.X,r1.Y),p,a);
Point p2=PRotate(new Point(r1.X+r1.Width,r1.Y),p,a);
Point p3=PRotate(new Point(r1.X+r1.Width,r1.Y+r1.Height),p,a);
Point p4=PRotate(new Point(r1.X,r1.Y+r1.Height),p,a);
g1.DrawLine(pen,p1,p2);
g1.DrawLine(pen,p2,p3);
g1.DrawLine(pen,p3,p4);
g1.DrawLine(pen,p4,p1);
}
//调用方法
private void panel1_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
{
Rectangle r1=new Rectangle(80,80,30,40);
e.Graphics.DrawRectangle(new Pen(Color.Red),r1);
DrawRotateRect(r1,new Point(80,80),90,e.Graphics,new Pen(Color.Blue)); }

Answer 2

楼上说的是，如果使Graphics旋转，则旋转前要保存它的状态，旋转后再还原回来

Answer 3

但是，使用Graphics旋转和其它变换，是最方便的