使用Visual Basic更改线条颜色

Question

我创建了此代码以创建一行。我用一种算法产生一条水平线

Dim x1 As Integer
Dim y1 As Integer
Dim x2 As Integer
Dim y2 As Integer
Dim grp As Graphics
Dim img As New Bitmap(1, 1)

Public Function intial()
    a = drawingBox.Width / 2
    b = drawingBox.Height / 2
    grp = drawingBox.CreateGraphics()
    grp.TranslateTransform(a, b)
    grp.ScaleTransform(1, -1)

End Function

Public function line()
    y=y1
    for x=x1 to x2 then
         grp.DrawImage(img, x, y)
    next
End Function

Private Sub btnLine_Click(sender As Object, e As EventArgs) Handles btnLine.Click

    x1 = tbX1.Text
    y1 = tbY1.Text
    x2 = tbX2.Text
    y2 = tbY2.Text

    img.SetPixel(0, 0, Color.Black)

    line()


    tbX1.Clear()
    tbY1.Clear()
    tbX2.Clear()
    tbY2.Clear()

End Sub

任何想法，即使我画了很多线，也要如何改变我制作的线？ （请更改我已经在图片框中输入的每一行） 谢谢！