VB/C#:在全局范围内放置可处置对象:这样可以吗?

作为一种优化,我决定在全局范围内放置一个我经常需要的对象——一个SDL曲面,带有整个级别的预渲染图像(称为S_AreaBMP)。
现在它不必在每一帧的DrawScreen函数中创建和销毁。我只需要在加载新关卡或GFX表时处理和更改它,我通过以下功能执行此操作:

Public Sub PrepareAreaImage()

    ''#dispose old image before it becomes unreferenced
    If AreaBMPExists
        S_AreaBMP.Dispose()
    End If
    AreaBMPExists = True

    ''#declare an appropriately sized bitmap w/ a GDI Graphics object
    Dim AreaBMP As Bitmap = New Bitmap(Area.W * TLDIM, Area.H * TLDIM)
    Dim AreaGrph As Graphics = Graphics.FromImage(AreaBMP)

    ''#...(omitted: iterate through Area and draw each tile to AreaBMP)

    ''#Store to the SDL surface
    S_AreaBMP = New SdlDotNet.Graphics.Surface(AreaBMP)

    ''#Dispose
    AreaBMP.Dispose()
    AreaGrph.Dispose()
End Sub

(AreaBMPExists和S_AreaBMP是全局范围)

问题:

它工作得很好,但我忍不住觉得这种事情是令人沮丧的。。。