用C#画圆

Form程序,直接用PictureBox就行了
画圆：无填充色

private void button1_Click(object sender, EventArgs e)
        {
            Graphics gra = this.pictureBox1.CreateGraphics();
            Pen pen = new Pen(Color.Pink);//画笔颜色
            gra.DrawEllipse(pen, 10, 10, 100, 100);//画椭圆的方法，x坐标、y坐标、宽、高，如果是100，则半径为50
         }

画圆：有填充色

private void button1_Click(object sender, EventArgs e)
        {
            Graphics gra = this.pictureBox1.CreateGraphics();
            Brush bush = new SolidBrush(Color.Green);//填充的颜色
            gra.FillEllipse(bush,10,10,100,100);//画填充椭圆的方法，x坐标、y坐标、宽、高，如果是100，则半径为50
        }

以下是web程序，需要保存。

int w = Convert.ToInt32(TextBox1.Text) * 2;
int h = Convert.ToInt32(TextBox1.Text) * 2;
Image1.Width = w;
Image1.Height = h;
Bitmap bmp = new Bitmap(w, h);
Graphics g = Graphics.FromImage(bmp);
g.FillEllipse(new SolidBrush(Color.Red),0,0,w,h);
bmp.Save(Server.MapPath("~/a.bmp"));
Image1.ImageUrl = "~/a.bmp";
g.Dispose();