画圆盘的指针

       private Bitmap GetPointerImg(Bitmap pointerImg, float angle, int w, int h ,int centerX, int centerY)
        {
            // 创建新的位图作为旋转后的图片
            Bitmap rotatedImage = new Bitmap(w, h);

            // 创建一个Graphics对象，用于绘制旋转后的图片
            using (Graphics g = Graphics.FromImage(rotatedImage))
            {
                g.FillEllipse(new SolidBrush(Color.Red), new Rectangle(centerX, centerY, 10, 10));

                // 设置旋转中心点为图片中心
                g.TranslateTransform(centerX, centerY);

                // 执行旋转
                g.RotateTransform(angle);

                // 恢复旋转中心点到原位置
                g.TranslateTransform(-centerX, -centerY);

                g.DrawImage(pointerImg, 0, centerY - pointerImg.Height / 2);
            }
            return rotatedImage;
        }

        private void pictureBox1_Click(object sender, EventArgs e)
        {
            int centerX = pictureBox1.Width / 2;
            int centerY = pictureBox1.Height / 2;
            var ea = (MouseEventArgs)e;
            double distance = Math.Sqrt(Math.Pow(ea.X - centerX, 2) + Math.Pow(ea.Y - centerY, 2));//点击处到圆心的距离
            double angle = Math.Asin((centerY - ea.Y) / distance) * 180 / Math.PI;
            if (centerX < ea.X && centerY > ea.Y) angle = 180- angle;//第一象限
            else if (centerX > ea.X && centerY < ea.Y) angle = 0;//第三象限
            else if (centerX < ea.X && centerY < ea.Y) angle = 180;//第四象限
            //double angle = 180 / (Math.PI * Math.Atan((centerY - ea.Y) / 1.0 * (centerX - ea.X)));
            text_Angle.Text = angle.ToString();
            var bmp = GetPointerImg(Resources.valsalvaThresholdPointer, (float)angle, pictureBox1.Width, pictureBox1.Height, 124, 124);
            pictureBox1.Image = bmp;
        }

        private void btn_DrawPointer_Click(object sender, EventArgs e)
        {
            var angle = Convert.ToDouble(text_Angle.Text);
            var bmp = GetPointerImg(Resources.valsalvaThresholdPointer, (float)angle, pictureBox1.Width, pictureBox1.Height, 124, 124);
            pictureBox1.Image = bmp;
        }