Recursive Portal Nesting

What this builds

A portal that correctly shows other portals inside itself, to a controlled depth. Two portals facing each other produce the classic infinite corridor; a mirror facing a mirror produces an infinite regress. Both are the same problem: the portal view contains the portal, so rendering it requires rendering itself.

• Bounded recursion with an explicit depth limit and a terminating frame
• Ping-pong render targets so depth N samples depth N+1's output
• Per-level camera transforms composed from the base portal transform
• Per-level oblique near planes, recomputed at every depth
• Automatic depth reduction under frame-time pressure
• A believable terminal frame so the deepest level does not read as a hole

When to use / when not to