Lifts dont work properly

[Cavencruiser]

This makes it so that sometimes it's impossible to beat the icon of sin and causes an issue on level 13, where if you fall off the rising elevator lift before it reaches the top, run out of the room and reenter it, the lift will lock up and you cant get the yellow key in doom 2

[doomhack]

Strange. As far as I can see Map 30 is working as expected.

Googling shows that there is a game bug on Map13 Yellow key lift.

https://steamcommunity.com/app/208200/discussions/0/522730535768373433/

Though this one does seem to be a Save-reload bug which shouldn't affect us...

[Cavencruiser]

The issue is more prominent in fan mods like momento mori, where lifts would just stop working. Also this occasionally happens in doom 2 with the crusher level

[Cavencruiser]

ok, so this also seems to effect e2m2 in doom 1 at the area with the segmented circle type object with multiple raising platforms. It doesn't want to work sometimes which ends up causing a SoftLock if you happen to fall into the area where it normally should lift you back up. give the level a try and go to this spot last after doing everything in the map. It probably would be locked up. I believe it has something to do with plats.c

[doomhack]

See if I can figure it out.

When doing code fixes to make it compile cleanly in GCC14, I did fix some of the platform code bugs with pointer indirection level. (** being treated as *)

[Cavencruiser]

the "fixed" code I posted didnt work and resulted in the same behavior. How can we go about fixing this issue?

[doomhack]

If we can find a way to reliably repro the issue, we can fix it.

I tried just standing near the lifts and they kept going for 30 mins or so, but when I walked around the level collecting the keys, they were stopped when I came back.

Strange bug.

[Cavencruiser]

If we can find a way to reliably repro the issue, we can fix it.

I tried just standing near the lifts and they kept going for 30 mins or so, but when I walked around the level collecting the keys, they were stopped when I came back.

Strange bug.

HOLY MOLY, I FOUND HOW TO REPRODUCE IT!
ok, so first activate the lifts by going near them, first thing you do. Then second go directly to the room where you find the secret plasma rifle. Pull the lever, dont get the rifle and run back to the lifts. They are frozen! Hopefully this points in a direction that allows for a fix

[doomhack]

Great. Thanks. See if I can crack this one then!

[doomhack]

Seems to be the active platform lists getting messed up.

If we comment out P_AddActivePlat and P_RemoveActivePlat, the bug goes away...

[Cavencruiser]

Seems to be the active platform lists getting messed up.

If we comment out P_AddActivePlat and P_RemoveActivePlat, the bug goes away...

This isn't a fix though, right?

[doomhack]

No, not a fix. But it tells us where the bug is.

I think I've got a fix for it now. Also think might affect ceilings too as it uses similar code...

[doomhack]

Look at that bug!

void P_AddActivePlat(plat_t* plat)
{
platlist_t* old_head = _g->activeplats;

platlist_t *list = Z_Malloc(sizeof *list, PU_LEVEL, (void**)&_g->activeplats);
list->plat = plat;
plat->list = list;
if ((list->next = old_head))
    list->next->prev = &list->next;

list->prev = &old_head; //BUG!!!

}

We're setting list->prev to the address of a local var...

[doomhack]

I pushed a fix onto the V3 branch.