Vanilla Engine Questions

[MathsDevil]

Apologies if this already exists somewhere, however I find myself wondering things about the original Doom engine that don't seem to be answered on the Doom Wiki. 

[MathsDevil]

My question is: if Barrel A explodes near enough to Barrel B that Barrel B explodes and nothing else has caused damage or interfered in any way, what is the time interval between the two explosions?

I have carried out a few experiments and it seems to vary on a pseudo-random basis but is close to 0.37 seconds. 

Is there another way to work this out? I am trying to design a puzzle based on the timing of chains of barrels exploding in which each barrel only detonates the next one, and so on.

[scifista42]

The screenshot below is from WhackEd, a DEHACKED editor, showing the states that define animations and behavior of things in Doom.

 

 

Barrel death animation plays for 15 tics in total (the 3 highlighted states, each has duration 5 tics) before it causes an explosion by calling Explode in the very next state, upon which the explosion damages surrounding things immediately, and things (including other barrels) that take enough damage to be killed/destroyed will enter their death animations immediately.

 

Duration of the first state of the death animation is decreased by a random number between 0 and 3, inclusive. From P_KillMobj in Doom's source code:

 

    target->tics -= P_Random()&3;

    if (target->tics < 1)
	target->tics = 1;

 

Therefore the interval between barrel explosions varies between 12-15 tics on a pseudo-random basis. 1 tic = 1/35 of a second, so 12-15 tics correspond to roughly 0.34-0.42 of a second. Precisely, the interval is always either 12 tics ~= 0.34 seconds, 13 tics ~= 0.37 seconds, 14 tics ~= 0.4 seconds, or 15 tics ~= 0.42 seconds.

 

Edited January 31, 2018 by scifista42

[MathsDevil]

Thanks Scifista42, that's really helpful and corroborates my experimental evidence beautifully!