SpelunkyFan wiki

Olmec not slamming while drifting left

Verified against the spelunky.ai port v0.1.11 on .

Olmec not slamming while drifting left is a quirk of Spelunky Classic in which Olmec drifting left fast passes over the player without stopping to slam.

Olmec fights by hopping toward the player and stopping in the air over him, to slam down on him. The check that stops him treats left and right differently: drifting right, he stops over the player at once; drifting left at half his top speed or more, he passes over him.

What happens

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Olmec hops and drifts left over the player without stopping, and stops to slam only once his drift has slowed. On his next hop he drifts right and stops over the player at once [1].

Olmec doesn't stop to slam while drifting left. Olmec hops and drifts left over the player without stopping, and stops to slam only once his drift has slowed. On his next hop he drifts right and stops over the player at once.

Why

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In the air after a hop, Olmec's drift, xVel, goes up by 0.25 a step toward the player to 2 and back down again [2]. On every step he tests whether to stop and slam:

        if ((not oPlayer1.active and yVel >= 0) or
            (oPlayer1.y > y and abs(oPlayer1.x - (x+32)) < 32 and xVel > -1))
        {
            status = PREPARE;
            yVel = 0;
            xVel = 0;
            myGrav = 0;
            counter = 20;
        }
objects/oOlmec/step.gml:121-129, from spelunky.gmk, Spelunky Classic 1.1's source, © 2008, 2009 Derek Yu and Mossmouth, LLC (Spelunky User License v1.1b).

The player has to be below Olmec's top and within 32 pixels of his middle, and xVel greater than -1. A drift to the right always passes that last test, but a drift to the left of -1 or faster, half his top drift or more, fails it, so he goes on over the player [3].

Reproducing it

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Stand on Olmec's left as he hops: a fast drift toward the player carries him over without stopping. The replay of a whole game with seed 1 shows both sides: on one hop he drifts left over the player for 8 steps, his xVel -2 at the fastest, and stops only once it's back to -0.75. On his next he drifts right and stops over the player at once, with an xVel of 2 [4].

In the port

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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 his drift and the step he stops. No option turns it off.

FAQ

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Why does Olmec sometimes fly over the player without slamming?

Olmec stops over the player to slam only while his drift to the left is slower than a pixel a step. Drifting left any faster, he passes over the player and stops once his drift slows down again.

Does it matter which side of Olmec the player is on?

Yes. A hop toward a player on his left can carry him past before he stops, while one toward a player on his right stops over him at once, at any speed.

How fast does Olmec drift?

His drift speeds up by a quarter of a pixel a step to 2 and slows down again, and he moves twice that, so up to 4 pixels a step. He stops over a player on his left only while it's slower than 1.

See also

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References

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  1. Clip quirks/olmec-slam-drifting-left
  2. objects/oOlmec/step.gml:104-119
  3. Quirk 1 (docs/quirks.md)
  4. Replay fidelity/replays/ending-seed-1.txt

Source code

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