The user can click and draw to create the shape. Then the user releases the mouse, the program fills the shape with random line segments.

The following code shows how the program lets the user draw a shape.

' The points selected by the user.
Private ShapePoints As New List(Of Point)()
Private ShapePath As GraphicsPath = Nothing
Private LinesPath As GraphicsPath = Nothing
Private IsDrawing As Boolean = False

' Start drawing.
Private Sub Form1_MouseDown(ByVal sender As Object, ByVal e _
    As System.Windows.Forms.MouseEventArgs) Handles _
    Me.MouseDown
    ShapePoints = New List(Of Point)()
    ShapePoints.Add(e.Location)
    IsDrawing = True
    Refresh()
End Sub

' Continue drawing.
Private Sub Form1_MouseMove(ByVal sender As Object, ByVal e _
    As System.Windows.Forms.MouseEventArgs) Handles _
    Me.MouseMove
    If Not IsDrawing Then Return
    ShapePoints.Add(e.Location)
    Refresh()
End Sub

' Finish drawing.
Private Sub Form1_MouseUp(ByVal sender As Object, ByVal e As _
    System.Windows.Forms.MouseEventArgs) Handles Me.MouseUp
    If Not IsDrawing Then Return
    IsDrawing = False

    ' Generate the random lines to fill the shape.
    GenerateLines()

    Refresh()
End Sub

The MouseMove event handler adds a new point to ShapePoints if IsDrawing is true.

The MouseUp event handler calls GenerateLines if IsDrawing is true. The following code shows how GenerateLines works.

' Generate the random lines to fill the shape.
Private Sub GenerateLines()
    If ShapePoints.Count < 3 Then
        ShapePath = Nothing
        LinesPath = Nothing
        Return
    End If

    ' Make the shape's path.
    ShapePath = New GraphicsPath()
    ShapePath.AddPolygon(ShapePoints.ToArray())

    ' Get the shape's bounds.
    Dim bounds As RectangleF = ShapePath.GetBounds()
    Dim xmin As Integer = CInt(bounds.Left)
    Dim xmax As Integer = CInt(bounds.Right) + 1
    Dim ymin As Integer = CInt(bounds.Top)
    Dim ymax As Integer = CInt(bounds.Bottom) + 1

    ' Generate random lines.
    LinesPath = New GraphicsPath()
    Dim num_lines As Integer = CInt((bounds.Width + _
        bounds.Height) / 16)
    Dim rand As New Random()
    Dim x1, y1, x2, y2 As Integer
    For i As Integer = 1 To num_lines
        x1 = rand.Next(xmin, xmax)
        y1 = ymin
        x2 = rand.Next(xmin, xmax)
        y2 = ymax
        LinesPath.AddLine(x1, y1, x2, y2)
        x1 = xmin
        y1 = rand.Next(ymin, ymax)
        x2 = xmax
        y2 = rand.Next(ymin, ymax)
        LinesPath.AddLine(x1, y1, x2, y2)
    Next i
End Sub

The following code shows how the program draws the filled shape.

' Draw the shape.
Private Sub Form1_Paint(ByVal sender As System.Object, ByVal _
    e As System.Windows.Forms.PaintEventArgs) Handles _
    MyBase.Paint
    ' Draw the shape.
    If IsDrawing Then
        ' Draw the lines so far.
        If ShapePoints.Count > 1 Then
            e.Graphics.DrawLines(Pens.Green, _
                ShapePoints.ToArray())
        End If
    Else
        ' Fill and outline the finished shape.
        If ShapePath IsNot Nothing Then
            e.Graphics.FillPath(Brushes.LightGreen, _
                ShapePath)
            e.Graphics.DrawPath(Pens.Green, ShapePath)

            ' Fill with the lines.
            e.Graphics.Clip = New Region(ShapePath)
            e.Graphics.DrawPath(Pens.Green, LinesPath)
        End If
    End If
End Sub

If the user is not currently drawing, the program fills the shape's path and outlines it. Next it sets the Graphics object's clipping region to the path the user drew. It then draws the lines, which are clipped by the clipping region.