给你完整做了一个

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Q717883
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            currPt = new Point(0, 0);
        }

        private Point currPt { get; set; }

        private void pictureBox1_Paint(object sender, PaintEventArgs e)
        {
            e.Graphics.FillRectangle(Brushes.White, pictureBox1.DisplayRectangle);
            foreach (var line in textBox1.Lines.Select(x => x.ToLower().Trim()).Where(x => x != ""))
            {
                if (line.StartsWith("moveto"))
                {
                    int x = int.Parse(line.Replace("moveto", "").Replace(" ", "").Trim().Split(',')[0]);
                    int y = int.Parse(line.Replace("moveto", "").Replace(" ", "").Trim().Split(',')[1]);
                    currPt = new Point(x, y);
                }
                else if (line.StartsWith("circle"))
                {
                    int r = int.Parse(line.Replace("circle", "").Trim().Split(',')[0]);
                    e.Graphics.DrawEllipse(Pens.Black, currPt.X - r, currPt.Y - r, r + r, r + r);
                }
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            pictureBox1.Refresh();
        }
    }
}

namespace Q717883
{
    partial class Form1
    {
        /// <summary>
        /// Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            this.textBox1 = new System.Windows.Forms.TextBox();
            this.button1 = new System.Windows.Forms.Button();
            this.pictureBox1 = new System.Windows.Forms.PictureBox();
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox1)).BeginInit();
            this.SuspendLayout();
            // 
            // textBox1
            // 
            this.textBox1.Location = new System.Drawing.Point(11, 14);
            this.textBox1.Multiline = true;
            this.textBox1.Name = "textBox1";
            this.textBox1.ScrollBars = System.Windows.Forms.ScrollBars.Both;
            this.textBox1.Size = new System.Drawing.Size(207, 386);
            this.textBox1.TabIndex = 0;
            this.textBox1.Text = "moveTo 100,100\r\ncircle 20";
            // 
            // button1
            // 
            this.button1.Location = new System.Drawing.Point(130, 408);
            this.button1.Name = "button1";
            this.button1.Size = new System.Drawing.Size(87, 26);
            this.button1.TabIndex = 1;
            this.button1.Text = "draw";
            this.button1.UseVisualStyleBackColor = true;
            this.button1.Click += new System.EventHandler(this.button1_Click);
            // 
            // pictureBox1
            // 
            this.pictureBox1.Location = new System.Drawing.Point(227, 15);
            this.pictureBox1.Name = "pictureBox1";
            this.pictureBox1.Size = new System.Drawing.Size(473, 418);
            this.pictureBox1.TabIndex = 2;
            this.pictureBox1.TabStop = false;
            this.pictureBox1.Paint += new System.Windows.Forms.PaintEventHandler(this.pictureBox1_Paint);
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(714, 446);
            this.Controls.Add(this.pictureBox1);
            this.Controls.Add(this.button1);
            this.Controls.Add(this.textBox1);
            this.Name = "Form1";
            this.Text = "Form1";
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox1)).EndInit();
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        #endregion

        private System.Windows.Forms.TextBox textBox1;
        private System.Windows.Forms.Button button1;
        private System.Windows.Forms.PictureBox pictureBox1;
    }
}

你先要知道怎么去画圆，你所说的无非就是参数问题，你是不是应该先考虑怎么画一个固定的圆，然后将参数提取出来？