# Optically Illusory

21 March 2014 2 Comments

I came across a charming little optical brain-bender a while back, and wondered what would be needed to reproduce it in Excel/VBA. Not much, as it transpired (see below). I’ve golfed the code somewhat for brevity. Dump the following in an empty VBA module and run “DrawIllusion”…

Private pi As Single Public Sub DrawIllusion() Dim shp, c pi = WorksheetFunction.pi() ActiveWindow.DisplayGridlines = False For Each shp In ActiveSheet.Shapes: shp.Delete: Next NewShape 0, 0, 420, 0, vbWhite For c = 1 To 4: DrawACircle 200, 200, 60 + (c - 1) * 40, 15, 5, -20 + (c Mod 2) * 40: Next End Sub Private Sub DrawACircle(x, y, r, side, gap, rotationOffset) Dim numSquares, i, angle, shp numSquares = NumToDraw(r, side, gap) For i = 1 To numSquares angle = (i - 1) * 2 * pi / numSquares Set shp = NewShape(x + r * Cos(angle), y + r * Sin(angle), side, angle * 180# / pi, IIf(i Mod 2 = 1, vbBlack, vbWhite)) shp.Rotation = shp.Rotation + rotationOffset Next End Sub Private Function NumToDraw(r, side, gap) NumToDraw = Int(2 * pi * r / (side + gap)) NumToDraw = NumToDraw - NumToDraw Mod 2 End Function Private Function NewShape(x, y, side, rot, color) Set NewShape = ActiveSheet.Shapes.AddShape(msoShapeRectangle, x, y, side, side) NewShape.Rotation = rot NewShape.Line.ForeColor.RGB = color NewShape.Line.Weight = 1 NewShape.Fill.ForeColor.RGB = RGB(128, 128, 128) End Function

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Very nice.

Any particular reason for declaring pi as a single? I know drawn shapes only work in single precision, but is there any down side to using doubles for constants?

It just saves thinking about it if you make everything double (or long).

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