[firedrake] Reconstructing a symmetric solution form the part for visualisation purposes

Dear all, I have a partial differential equation on a square and because of the symmetry of the problem, instead I'm solving equation on the triangle with appropriately changed boundary conditions. For visualisation purposes I want to re-create full square composed from 8 triangles. What is the simplest way to achieve it? I can always go with an image editor, but this is not the route I'd wish to take (and also, this way it would be hard to automate). Sincerely, George