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Doom gravity metrics

PostPosted: Thu Sep 16, 2021 12:01 am
by Matt
After 1 second of falling from a standstill, a typical gravity 1.0 actor will be falling at a speed of 35 units per tic.

This translates to 35x35 units per second - 1225.

On Earth, ignoring air resistance, an object after falling one second will be falling at a speed of 9.8 metres per second.

If we suppose Doomguy's 56 units to be a little less than 2m, we can rough out 60 units to be 2m - or 30 units as 1m.*

This means that if Doom's gravity were made similar to IRL, after 1 second of falling a gravity 1.0 actor would be going at 30x9.8 units per second - 294.

Am I missing something? Is Doom's gravitation acceleration really up to four times what we see in real life!?

*(The current dev version of HD sets this at 37 but that's only because it emphasizes horizontal distances and multiplies the relevant formula by 1.2 while also presupposing a much shorter doomguy.)

Re: Doom gravity metrics

PostPosted: Thu Sep 16, 2021 12:42 am
by Gez
The first tic of freefall, you fall at a speed of 2, instead of just 1. So after a full second, you reach a speed of 36. Does it make sense? No, but that's how it works.

See falling damage for a lot of nerdery about it, including a chart and a table.

Re: Doom gravity metrics

PostPosted: Thu Sep 16, 2021 2:22 am
by Matt
My point is trying to figure out how much the end result corresponds or not with its IRL equivalent.

Anyway, I'm messing around with reduced gravity here and I think I get why it looks so weird - in normal play everything's just this tiny little action figure in a box in front of us and the faster falling speed just makes more sense for something that we intuit is very small.

I think I'll be going ahead with this change in HD.

Re: Doom gravity metrics

PostPosted: Thu Sep 16, 2021 4:33 am
by Gez
Yeah, the proportions in Doom are all out of whack (a well-known fact) so there's a lot of stuff that isn't really realistic. Like famously the torso-level view height, or Doomguy's jet-powered running speed.

Re: Doom gravity metrics

PostPosted: Thu Sep 16, 2021 4:40 am
by Enjay
And the fact that every map unit is 1.2 times taller than it is wide.

Yet somehow it all comes together to create one of the most addictive gaming experiences ever because it feels so right, despite being so very wrong.

Re: Doom gravity metrics

PostPosted: Sat Sep 18, 2021 1:09 am
by Graf Zahl
Trying to do IRL in Doom is either doomed to fail or failed to Doom, choose whatever makes more sense. :P

Re: Doom gravity metrics

PostPosted: Sat Sep 18, 2021 5:14 am
by Rachael
Doom Guy is just Superman in disguise. Except without the laser eyes and the flying.

And his kryptonite is bad level design and sadistic/evil/both gameplay modders. ;)

That is my story and I am sticking with it!

Re: Doom gravity metrics

PostPosted: Sat Sep 18, 2021 9:19 am
by InsanityBringer
I once made a mod for novelty purposes where the walk speed was fixed to roughly 1 m/s (using 8MU as one foot) and realistic gravity (accounting for the 1.2 aspect ratio scaling on the z axis) and it was on that day I realized how large Doom levels truly are. I also made one with realistic Phobos gravity, which required basically loading a grappling hook mod or something to actually stay attached to the floor.

Re: Doom gravity metrics

PostPosted: Sat Sep 18, 2021 12:44 pm
by NeuralStunner
As far as metric scaling, I had settled on the grid-friendly 32u to 1m. Works best for new projects, at 56u Doomguy comes out to 1.75m or 5'9". If you apply aspect correction unfortunately makes it utterly ridiculous, he'd be pushing 7ft. Maybe he comes from Death Valley.

Re: Doom gravity metrics

PostPosted: Thu Nov 18, 2021 10:37 pm
by determin1st
i did some bullet speed calculations recently, it's assumed to fly horizontally but i figured out some numbers..

assuming 32 units = 1 vertical meter,
the doomguy as 1.75m tall (56 units)

acceleration is 9.8m/s, so, let's calculate the velocity at 2nd second

v = 9.8 * 32 = 313.6 units/sec

so generally you're right, but in manual of the speed it says that ticks are about projectiles, not the monster/player, so, i suppose some tests should be done to log actual velocity, maybe there is another formula, because speed=1225 is faster than my calculated muzzle velocity speed=510 of the 440 m/s .357 magnum bullet :shock:

Re: Doom gravity metrics

PostPosted: Fri Nov 19, 2021 9:46 am
by Caligari87
Ultimately anything attempting to use "real world" units in Doom must make some concessions because the maps, physics, and visuals were definitely not designed to meet real world specifications in any way. Aspect ratio scaling, viewheight, and player speed all muck with this.

As one might expect, Hideous Destructor seems to have gotten things as close as it's possible to get within the confines of standard Doom levels and graphics.

Obviously for standalone projects it's less of a concern as you can set up the metrics however you want, disable aspect scaling, etc. Personally I went with 64mu / meter and then set up a bunch of constant values so I can do stuff like (175*CM) and have it Just Work™ without too much thought.


Re: Doom gravity metrics

PostPosted: Fri Nov 19, 2021 1:23 pm
by Reactor
Well don't forget that the first Doom took place on Phobos, Deimos and eventually Hell...gravitational pull might be a tad different there ;)

Re: Doom gravity metrics

PostPosted: Fri Nov 19, 2021 1:47 pm
by Caligari87
Doesn't really track, because by any reasonable metric that assumes Doomguy is close to human size (even with warped and inconsistent sizes), gravity in Doom is stronger than Earth gravity by a lot ... Which is the whole point of this thread. Hell is a fictional place so it doesn't count, but Phobos and Deimos are definitely much smaller than Earth so gravity would be a lot weaker.

Alternatively, it's a game and they designed something that plays well, realism be damned.


Re: Doom gravity metrics

PostPosted: Fri Nov 19, 2021 5:16 pm
by determin1st
you only have to track 35 ticks, maybe twice, to determine the velocity obtained by Y axis, so you'll get the magic number of 1.0 gravity. then you may tune it to the real world value or to the unreal world value. the Q is that number, maybe ill measure it later.. have to make bullet ballistics first :P

Re: Doom gravity metrics

PostPosted: Sun Nov 21, 2021 7:47 am
by TheRailgunner
So, idea: what if someone scaled almost everything down - levels, actors, projectile speeds, the player's viewheight, and so on - to a ratio that allows Doom's gravity (probably also adjusted) to approximate the real-world acceleration of 9.8m/s?

Would roughly 1/4th scale work here? Working from the "32u=1m,56u=1.75m Doomguy" ratio, would a 8u meter with a 14u-tall Doomguy at a viewheight of 10 or 11 be usable as a more realistic starting point (with DG normally being 56u tall with a viewheight of 41)?

Sorry if there's something I'm missing here, I just woke up.