Computes the center-to-vertex distance for a cell with this geometry
Hexagonal tiling goes from vertex to edge, r is a function of hScale such
that the NW vertex to E edge distance = hScale, also the top to bottom
edge distance is vScale.
Computes the line which frames this wall of the given cell
Use the following:
Polygon p= wallPoly( x, y, dir );
drawLine( p.xpoints[0], p.ypoints[0], p.xpoints[1], p.ypoints[1] );