本文是一个实现手写板的简单小示例，当鼠标按下时开始写字，鼠标松开时停止写字。

原理非常简单，当触发MouseDown事件时记录起始坐标startPoint，随着鼠标的移动触发MouseMove事件，记录当前坐标currentPoint，并以startPoint和currentPoint两点画直线，刷新startPoint的坐标。

实现代码如下：

Public Class Form1
    Private graphics As Graphics
    Private startPoint As Point
    Private currentPoint As Point
    Private flagDraw As Boolean

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        graphics = Me.CreateGraphics
    End Sub

    Private Sub Form1_MouseDown(sender As Object, e As MouseEventArgs) Handles Me.MouseDown
        startPoint = e.Location
        flagDraw = True
    End Sub

    Private Sub Form1_MouseMove(sender As Object, e As MouseEventArgs) Handles Me.MouseMove
        If flagDraw Then
            currentPoint = e.Location
            graphics.DrawLine(New Pen(Brushes.Black), startPoint, currentPoint)
            startPoint = currentPoint
        End If
    End Sub

    Private Sub Form1_MouseUp(sender As Object, e As MouseEventArgs) Handles Me.MouseUp
        flagDraw = False
    End Sub

End Class