[.NET] graphics的問題

[applerev (亞拉那以嘎?)]

請輸入專案類型(網站專案或者應用程式專案)：windows應用程式

=======================================
Public Class Form1
    Dim g As Graphics = Me.CreateGraphics
    Dim pen As New Pen(Color.Brown, 1)

    Private Sub btnTriangle_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnTriangle.Click
        g.DrawRectangle(pen, 100, 100, 300, 300)
    End Sub
End Class
=======================================
Public Class Form1
    Dim pen As New Pen(Color.Brown, 1)

    Private Sub btnTriangle_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnTriangle.Click
        Dim g As Graphics = Me.CreateGraphics
        g.DrawRectangle(pen, 100, 100, 300, 300)
    End Sub
End Class
=======================================

我想請問一下

上面兩個差別在於宣告g的位置的程式

第二種可以正常繪出四邊形

但是第一種好像超出某個範圍會被裁切

請問造成這情形的原因在哪裡?

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