Parachutes torn only moving right or down

Verified against the spelunky.ai port v0.1.10 on 28 October 2026.

The open Parachute is torn by items that touch it, but only those moving right or down. The test looks at the item's speed one way on each axis, so an item crossing it to the left, or straight up, passes through, and the same item crossing it to the right tears it.

Floating down a shaft, the player throws a Rock up at the wall beside him. It bounces back left through the canopy, which holds. In the next shaft he throws one at the other wall: it bounces back right through the canopy, which tears away, and he drops ^[1].

The open parachute (oParachute) follows the player, a dome over his head ^[2]. Its collision with an item replaces it with the spent canopy, oParaUsed, which falls away:

if (other.xVel > 0 or other.yVel > 0)
{
    instance_create(x, y, oParaUsed);
    instance_destroy();
}

xVel > 0 is moving right and yVel > 0 is moving down, so an item moving left or straight up, or not moving, tears nothing. What reaches a dome over his head is an item falling onto it, which always tears it, or one flying up through it, which tears it only moving right ^[3].

Open the Parachute in a shaft and throw a Rock up at the wall on the player's right, so it comes back left through the canopy: it holds. Thrown at the left wall, it comes back right and tears it. Play reaches it with any item thrown or bounced up through an open parachute. The replay of the clip's staged scene, on a custom level, does both: the Rock that crosses the canopy moving left and up leaves it whole until he lands, and the one moving right and up tears it at once ^[4].

The spelunky.ai port reproduces it exactly: it's in docs/quirks.md's list of the 1.1 source's bugs ^[3], and the oracle's fingerprint of the replay pins both crossings. No option turns it off.