SWIsland Recursion Saga

Stage 3 makes the recursion visible. Instead of asking you to click each cell manually (Stage 2), the algorithm now grows the island itself — but at a pace you control, so you can watch every decision it makes.

The Algorithm

This is a direct JavaScript port of Island.grow() from the Java source. It uses recursive backtracking:

1. Base case: the island already has targetSize cells → done, return true.
2. Collect candidates: find every cell orthogonally adjacent to the island that is still water.
3. Shuffle (if Randomize is ON): randomly reorder candidates using Fisher-Yates → produces organic shapes. With Randomize OFF the candidates are sorted top→left→right→down, giving predictable boxy shapes every time. This is the only difference between an “organic” and a “non-organic” island.
4. Try each candidate:
   • ADD the cell (mark as land, add to island list).
   • Recurse — call grow() again from the new state.
   • If recursion returns true → success, propagate it up.
   • If recursion returns false → BACKTRACK: remove the cell and try the next candidate.
5. If all candidates fail → return false (signal the caller to backtrack).

Why Pre-record Then Replay?

JavaScript recursion runs to completion in one go — you can’t pause it mid-call to draw a frame. So Stage 3 runs the full grow() synchronously first, recording every ADD and BACKTRACK decision in a step queue. The p5.js draw() loop then replays that queue one step per frame at whatever speed you choose. The algorithm is real recursion; the animation is a replay.

Controls

• Target size — how many cells the island should have (1–20, including the seed).
• Speed — 1 is slowest (~2 seconds per step), 10 is fastest (one step every frame). Use slow speeds to follow the recursion log entry by entry.
• Randomize ON/OFF — compare organic vs. deterministic growth by running the same seed with the toggle in each position.
• Start / Pause / Resume — available after placing the seed; Spacebar also toggles.
• Clear — resets everything; C also works.

Reading the Recursion Log

• ▶ ADD (r, c) — algorithm just placed this cell and is recursing deeper.
• ✗ BACKTRACK (r, c) — that path failed; the cell was removed.
• ✓ SUCCESS — the island reached its target size.
• ✘ FAIL — the seed location was completely surrounded before the target was reached.