如何水平翻转层的几何图形？

Public Sub HorizontalFlip()
'Corrected after Bryco's hint about variable declaration syntax (ver. below). 
'Now it works!
Dim Thingy As AcadEntity
Dim LayerName As String
Dim MostLeftX as Double, MostRightX As Double  'thanks Bryco!
Dim BBoxMin, BBoxMax 'variants, will later be specified by GetBoundingBox
Dim FlippointA(0 To 2) as Double, FlippointB(0 To 2) As Double 'thanks Bryco!
MostLeftX = 2147483647: MostRightX = -2147483647
LayerName = "0" 'can be any valid layername
For Each Thingy In ThisDrawing.ModelSpace
    If Thingy.Layer = LayerName Then
        Thingy.GetBoundingBox BBoxMin, BBoxMax
        If BBoxMin(0)  MostRightX Then MostRightX = BBoxMax(0)
    End If
Next
'I now have MostLeftX and MostRightX for all geometry on layer.
'next, I define the mirror line, halfway between MostLeftX and MostRightX
FlippointA(0) = (MostLeftX + MostRightX) / 2: FlippointB(0) = FlippointA(0)
FlippointA(1) = 0: FlippointB(1) = 1
FlippointA(2) = 0: FlippointB(2) = 0 'endpoints of the vertical mirror line
'finally, I want to horizontally flip all entities on the layer
For Each Thingy In ThisDrawing.ModelSpace
    If Thingy.Layer = LayerName Then
        Thingy.Mirror FlippointA, FlippointB        'thanks Dnereb!
        Thingy.Delete
    End If
Next
End Sub