Previously every frame: cleared+redrawed 868 cells for coins, cleared+
redrawed all UI text, emptied+recreated pause layer, and swapped key
sprites repeatedly.
Now uses dirty flags and cached values:
- Coins: only redrawn when coins-dirty? is set (on coin eat/key pickup)
- Maze: only redrawn when a door is removed
- UI: only redrawn when score or time string actually changes
- Key: sprite swap happens exactly once, not every frame
- Pause: layer only modified when paused? state transitions
Exposes mark-coins-dirty! and mark-maze-dirty! messages so the game
ADT can signal changes from the level.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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