Why don't enemies climb the stairs to the blue armour secret of E1M1?

[plums]

On E1M1, enemies won't climb the stairs toward the blue armour from the underground tunnel. This is obvious if you press the button and run out to the armour, and look down the tunnel. The shotgun guy will climb one stair and then turn back down.

why?

I thought I understood monster behaviour well enough but I can't figure this one out. It only came to my attention because I'm tinkering on a ZDoom mod that replaces enemies, and the replacement does climb the stairs happily. The wiki does say that monster stair mechanics are "unclear", but also that faster monsters have more trouble on stairs; in my case, the replacement monster is faster -- speed 12. Slowing him back down to 8 keeps him in the tunnel.

Also, opinions as to whether or not this behaviour was intentional in the level design?

[clamgor]

Probably intentional, if they had the ability to climb those stairs... then Phobos would be fucked.

P.S. I was about to suggest that there might be a 'monster block' linedef, but then I read more of your statement.

[printz]

It's simple: a monster's bounding box mustn't be anywhere more than 24 units above ground. Steep stairs guarantee that's gonna happen.

[Tristan]

None of the stairs block monsters

[plums]

printz said:

It's simple: a monster's bounding box mustn't be anywhere more than 24 units above ground. Steep stairs guarantee that's gonna happen.

Aha, so the stairs aren't wide enough for him to get to the second stair without still hanging over the ground. That makes sense, thanks!

I guess a faster monster can move more distance in one tic, so he can move to a spot on the stairs where he isn't hanging over the ground still?

tested: The stairs are 32 units wide, and the Shotgun guy has a width of 40, meaning speed 8 is just slow enough to not make it up. At speed 9 he can, though he has some trouble, since he's only got a margin of one pixel. At speed 10 and up it's fairly easy for him. Groovy.

[Darch]

If you are using decorate, you can raise his MaxStepHeight to 32, he will have less troubles with stairs.

[plums]

Ideally I'd like my replacement monster to *not* those climb stairs, but I don't want to lower his speed either, and I definitely don't want to lower his MaxStepHeight because that will surely break a lot of levels. It's not a big deal though, I was more curious than anything.

[Zed]

Well, from a non-expert point of view, there's an option in PrBoom which allows you to define if monsters will or will not climb stairs. I find it quite reliable (I have it on by default and it doesn't breaks/desync demos, for example).

[vdgg]

In playback mode all these options are ignored. PrBoom+ chooses the same set of options which was set by the recorder. The post above finally made me start a PrBoom+ tutorial, something I was thinking about for a long time.