This allows actors to perform draw commands in TickDraw(), even
if it’s not exactly what we want in the future.

Not all programs support this feature for now, but that’s because they
don’t support the scene framework either, and will need patching. Also
the default postprocess is deliberately exaggerated for now.

Now TickDraw() can be called several times per frame, because we
may have several scenes. This is expected, but it will require
some adjustments later.