How does monster speed work?

[Salt Miner]

I wasn't sure where to put this but I was wondering if anyone can help answer this question I have on how monster speed works in the original games. I found on a doom wiki (and also in the source code) that (just for an example) the zombieman has a speed of 8 map units per frame, yet it also says that it moves 70 map units a second. I don't understand how this works out.

 

The second thing I don't understand is that the shotgun guy also has a coded movement speed of 8, but his movement speed per second is 93.3. So the zombieman and shotgun both have the same movement speed per frame, but different movement speeds per second. I don't understand this. Can anyone help?

[andrewj]

A "sprite frame" lasts a certain number of tics.

 

A "tic" is 1/35th of a second.

 

Monsters perform a single move each sprite frame (simplifying a little bit) -- it is really a jump from the old position to the new position.  If the speed is the same but the sprite frames are shorter (less tics), a monster will move faster.

Edited August 12, 2020 by andrewj

[Nootrac4571]

Specifically, here's the relevant logic (in DECORATE code) for the zombieman:

 

POSS AABBCCDD 4 A_Chase

 

Meaning he moves 8 units every 4 tics, which is equal to 70 units/second

 

The Shotgun guy animates slightly more quickly:

 

SPOS AABBCCDD 3 A_Chase

 

He moves 8 units every 3 tics, which works out as 93.333 units/second.

[SilverMiner]

Wow, I didn't know that Shotgun zombie is faster than zombieman

[Salt Miner]

Cool. Thanks for the information.