C# 提供两种切割圆形图片的方式

效果：

        private void Form1_Load(object sender, EventArgs e)
        {
            string file =System.IO.Path.Combine(Environment.CurrentDirectory, @"11.jpg");
            try
            {
                Image i = new Bitmap(file);
                pbO.Image = i;

                pbD1.Image = WayOne(file);
                pbD2.Image = WayTwo(file);

                pbS1.Image = WaySOne(file);
                pbS2.Image = WaySTwo(file);

            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
        private Bitmap WayOne(string file)
        {
            using (Image i = new Bitmap(file))
            {
                Bitmap b = new Bitmap(i.Width, i.Height);
                using (Graphics g = Graphics.FromImage(b))
                {
                    g.FillEllipse(new TextureBrush(i), 0, 0, i.Width, i.Height);
                }
                return b;
            }
        }
        private Bitmap WayTwo(string file)
        {
            using (Image i = new Bitmap(file))
            {
                Bitmap b = new Bitmap(i.Width, i.Height);
                using (Graphics g = Graphics.FromImage(b))
                {
                    g.DrawImage(i, 0, 0, b.Width, b.Height);
                    int r = Math.Min(b.Width, b.Height) / 2;
                    PointF c = new PointF(b.Width / 2.0F, b.Height / 2.0F);
                    for (int h = 0; h < b.Height; h++)
                        for (int w = 0; w < b.Width; w++)
                            if ((int)Math.Pow(r, 2) < ((int)Math.Pow(w * 1.0 - c.X, 2) + (int)Math.Pow(h * 1.0 - c.Y, 2)))
                            {
                                b.SetPixel(w, h, Color.Transparent);
                            }
                }
                return b;
            }
        }

        private Bitmap WaySOne(string file)
        {
            using (Image i = new Bitmap(file))
            {
                Bitmap b = new Bitmap(i.Width, i.Height);
                using (Graphics g = Graphics.FromImage(b))
                {
                    g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                    using (System.Drawing.Drawing2D.GraphicsPath p = new System.Drawing.Drawing2D.GraphicsPath(System.Drawing.Drawing2D.FillMode.Alternate))
                    {
                        p.AddEllipse(0, 0, i.Width, i.Height);
                        g.FillPath(new TextureBrush(i), p);
                    }
                    //g.FillEllipse(new TextureBrush(i), 0, 0, i.Width, i.Height);
                }
                return b;
            }
        }
        private Bitmap WaySTwo(string file)
        {
            using (Image i = new Bitmap(file))
            {
                Bitmap b = new Bitmap(i.Width, i.Height);
                using (Graphics g = Graphics.FromImage(b))
                {
                    g.DrawImage(i, 0, 0, b.Width, b.Height);
                    int r = Math.Min(b.Width, b.Height) / 2;
                    PointF c = new PointF(b.Width / 2.0F, b.Height / 2.0F);
                    for (int h = 0; h < b.Height; h++)
                        for (int w = 0; w < b.Width; w++)
                            if ((int)Math.Pow(r, 2) < ((int)Math.Pow(w * 1.0 - c.X, 2) + (int)Math.Pow(h * 1.0 - c.Y, 2)))
                            {
                                b.SetPixel(w, h, Color.Transparent);
                            }
                    //画背景色圆
                    using (Pen p = new Pen(System.Drawing.SystemColors.Control))
                        g.DrawEllipse(p, 0, 0, b.Width, b.Height);
                }
                return b;
            }
        }