Interesting results.
r7395 works perfectly. I can jump into the vent near the blue keycard in E2L1 100% of the time with no problems.
in r7440, I cannot get into the vent on the upward part of the jump, but as I fall down I can usually get into the vent.
in r7618, it's almost impossible to get into the vent. Every once in a while (like about 10% of jumps) you can get into it when falling from the jump but not the way up.
To review, this can be replicated by making the following CON changes:
1) Change RUNNINGSPEED from 53200 to 48640. I also tested a value halfway between those two with the same results.
Note that change 1) is enough to make jumping into vents much less reliable by itself. But by changing jumping physics as well, it becomes nearly impossible.
2) Change jumping physics with the following CON code:
ifonwater iffloordistl 32 nullop else
ife player[].jumping_counter 901
{
setp[].jumping_counter 0
getp[].poszv zvel
add zvel 644
setp[].poszv zvel
}
Essentially what this code does is it interrupts the hardcoded sequence that manipulates the player's vertical velocity during a jump. Early in the jump, it caps the velocity and then just leaves it alone so that physics can take its course. Without this code, the vertical speed is manipulated every tic, actually pushing the player back down artificially fast. With the code above, the player has the same jumping height as in vanilla, but the jump takes longer to go up and down and feels more floaty (more realistic for the height the player reaches).