The Grace Window

Overview

Respawn points are fixed; hazards move. Sooner or later a player dies while a hazard is sitting over the respawn point — and without protection it hits them again the next frame, and again the frame after. Three lives in three frames, and the player never saw it happen. (Dash shipped this way; the first scripted attempt to win the game found it inside a minute.)

The fix is a grace window: a frame counter loaded on every respawn, during which damage checks are skipped. Two rules make it honest:

• Cover every damage source. Gate only the obstacle and the player dies to the spikes instead — the cascade just changes costume. One timer, checked at the top of every damage path.
• Make it visible. Blink the player’s sprite while the window lasts (hide it on a low bit of the timer). Fairness needs to be seen to be believed — the blink isn’t decoration, it’s the game telling the player the rules, and telling them when the protection ends.

Pseudocode

on_damage (still alive):
    lives -= 1
    respawn player at start
    hurt_timer = 60                     ; a second of grace

per-frame, before any damage check:
    if hurt_timer > 0:
        hurt_timer -= 1
        skip ALL damage checks this frame

sprite update:
    if hurt_timer > 0 and (hurt_timer AND %0100):
        hide player sprite              ; the blink: rules made visible
    else:
        draw player normally

Implementation Notes

6502 (NES — Dash): hurt_timer in zero page; the obstacle check opens with lda hurt_timer / bne skip, the spike check decrements it (one decrement per frame, whichever path runs), and the OAM update swaps the sprite’s Y to the off-screen value on hurt_timer AND #%00000100 — a 4-frame flicker.

6510 (C64 — Starfield): the death_timer doubles as the life-lost border flash and the invulnerability gate — the ship-versus-wave check is skipped while it runs. Same byte, both jobs: the feedback and the mechanics share a clock, so they can’t disagree.

Choose what the window forgives. Collision damage, yes. Falling off the world, usually not. Pickups keep working — the window gates harm, not interaction.

Don’t let movement freeze. The player must be able to walk out of danger during the grace — gate the damage checks, never the input or movement code.

Trade-offs

Aspect	Cost
CPU	One load/branch at the head of each damage path
Memory	One byte
Complexity	Low — the discipline is gating every path and showing it

When to use: any game with lives, respawning, and hazards that persist across the death.

When to avoid: one-life games and games where the respawn point is provably safe — though “provably” deserves a scripted check, not a feeling.

Benefits

• No death cascades — one mistake costs one life
• Seen fairness — the blink tells the player the rules in real time
• Tunable mercy — the window length is one byte of difficulty design