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Demo record / replay

src/io/demo.phel and src/core/rng.phel provide deterministic recording and replay for bug reproduction (issue #64). For the demo command, see the tech-talk showcase.

Seeded RNG

Every gameplay draw (level gen, enemy spawn and wander, loot, blood, angles) goes through one seeded Park-Miller LCG in core/rng. php/random_int cannot be seeded, so it cannot support replay or R (restart the same map). The seed and input stream determine the world frame by frame.

Format

A demo is the seed plus a per-frame [key-bytes, dt-ms] stream:

{"version": 1, "seed": 4242, "frames": [["w", 16], ["wa", 17]]}

frames->json and json->demo are pure and unit-tested. A version mismatch, malformed JSON, or a frame that is not a [string, number] pair parses to nil.

Record / replay

  • --record=FILE: each frame appends the live [keys, ms] and passes it through. The file is written on exit.
  • --demo=FILE: loads seed and frames, re-runs game-loop on the recorded input, and skips the start menu.

resolve-frame! runs once per frame from the play loop. Modes: :off (live), :record (tap live), :replay (substitute recorded). File IO stays in the loop, never in the pure tick-world. When a replay runs out of frames, resolve-frame! returns {:end? true} and the loop quits.