It's not a practical problem. Renderings are all based on fixed resolution, so the approximation doesn't have to be arbitrarily close. Note this doesn't mean

It's not a practical problem. Renderings are all based on fixed resolution, so the approximation doesn't have to be arbitrarily close. Note this doesn't mean most of the renderers aren't wrong in subtle and not so subtle ways ways, but that you can do something reasonably careful with it and not need unbounded computation.