wlgol/openspec/changes/archive/2026-11-08-gol-simulation/design.md

Design

Context

Input, placement, HiDPI, and grid are implemented. Simulation state (sim_paused, ACTION_PAUSE, ACTION_STEP, speed actions) exists but is unused. See proposal.md.

Goals / Non-Goals

Goals:

• Conway tick loop with adjustable interval.
• Pause/resume, stepping, speed control.
• Paused-only cell editing via mouse, including drag painting.

Non-Goals:

• Pattern detection or statistics.
• Undo/redo.
• Multi-threading.

Decisions

D1: Tick timing

• Use monotonic clock in the frame loop; accumulate elapsed time; when >= interval, compute next generation and reset accumulator.

D2: Next generation buffer

• Allocate a second grid buffer; compute into it, then swap pointers (or copy). Prefer swap of cells pointers with size unchanged.

D3: Editing while paused

• Pointer button handler sets/clears cells if sim_paused; drag paints using motion events while button held.

D4: Speed bounds

• Interval range 0.05s..1.0s (20 tps..1 tps), step factor 2.

D5: Default bindings

• Add p, n, +/- to default config (merge).

Risks / Trade-offs

• [Tick cost on large grids] -> grid is small (50x50), fine.
• [Editing during tick race] -> editing only while paused avoids races.

Open Questions

None.