c#窗体无法显示绘制的点

实验要求（用ArrayList类）：
(1) 当鼠标左键按下后，拖动鼠标可以在窗体上画出一系列点来，鼠标抬起则停止；
(2) 利用菜单设置线的颜色和粗细。
(3) 利用菜单实现线条的擦除。

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;
using System.Collections;

namespace DRAWING
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}

    ArrayList m_PointList = new ArrayList();

    int r = 255;
    int g = 0;
    int b = 0;

    int t = 5;

    Form2 f2 = new Form2();

    Form3 f3 = new Form3();

    bool LBtnDown = false;
    bool delP = false;

    private void 颜色ToolStripMenuItem_Click(object sender, EventArgs e)
    {
        if (f2.ShowDialog() == DialogResult.OK)
        {
            r = int.Parse(f2.Form2ValueR);
            g = int.Parse(f2.Form2ValueG);
            b = int.Parse(f2.Form2ValueB);
        }
    }

    private void 粗细ToolStripMenuItem_Click(object sender, EventArgs e)
    {
        if (f3.ShowDialog() == DialogResult.OK)
        {
            t = int.Parse(f3.Form3ValueT);
        }
    }

    private void Form1_Paint(object sender, PaintEventArgs e)
    {
       Graphics ghs = e.Graphics;
       foreach (Point p in m_PointList)
       {
            ghs.FillEllipse(new SolidBrush(Color.FromArgb(r, g, b)), p.X, p.Y, t, t);
       } 
    }

   private void Form1_MouseDown(object sender, MouseEventArgs e)
    {
        if (e.Button == MouseButtons.Left)
        {
            LBtnDown = true;
        }
    }

    private void Form1_MouseUp(object sender, MouseEventArgs e)
    {

        LBtnDown = false;
        delP = false;
    }

    private void Form1_MouseMove(object sender, MouseEventArgs e)
    {
        Point point = new Point();
        point.X = e.X;
        point.Y = e.Y;

        if (LBtnDown == true && delP == false)
        {
            m_PointList.Add(point);
        }

        if (delP == true && LBtnDown == true)
        {
            if (m_PointList.Contains(point))
            {
                m_PointList.Remove(point);
            }
        }

    }

    private void 擦除ToolStripMenuItem_Click(object sender, EventArgs e)
    {
        delP = true;
    }

}

}

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 DRAWING
{
public partial class Form2 : Form
{
public Form2()
{
InitializeComponent();
}

    public string Form2ValueR
    {
        get
        {
            return this.textBox1.Text;
        }
    }

    public string Form2ValueG
    {
        get
        {
            return this.textBox2.Text;
        }
    }

    public string Form2ValueB
    {
        get
        {
            return this.textBox3.Text;
        }
    }
}

}

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 DRAWING
{
public partial class Form3 : Form
{
public Form3()
{
InitializeComponent();
}

    public string Form3ValueT
    {
        get
        {
            return this.textBox1.Text;
        }
    }

}

}

我在运行时，没有任何显示，无法达到绘图效果。
我是按着课上给的模板填充的代码，看了几个小时，也没发现什么不对的，所以希望有人能 帮我看看，感谢各位了。