Area or volume?

Feedback and support for the PC version of Osmos
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Area or volume?

Postby Atom » Tue Nov 16, 2010 5:45 am

I have some questions:

1. Are motes 2D creatures or 3D? For example, when 2 motes of the same radius join, do the product have <square root of 2> times bigger radius or <cube root of 2> times bigger radius? Or maybe the power is different from 2 or 3?


2. Thanks to observations I collected some data about forces, but I still lack of some knowledge:

Warped Chaos:
Attractor - attractor: force is dual, negative, equal(?) and opposite , proportional to mass1*mass2/(r1*r2) like gravity in game?
Attractor - our mote: force is dual, equal(?) and opposite
Attractor - other mote: no idea

Epicycles:
Central attractor - side attractor: force is not dual
Side attractor - side attractor - zero?
Attractor - mote: force is not dual

As one might notive, some reactions aren't dual as it is said in intro ("For every action, there is an equal and opposite reacion" (Isaac Newton)). If it goes for me, I do not criticize it, as i think that gameplay is the most important. Realism should work for gameplay not the opposite way.

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eddybox
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Re: Area or volume?

Postby eddybox » Tue Nov 16, 2010 2:46 pm

Hi Atom,

Excellent questions!

1. They're usually 2D in the sense that radius is proportial to the square root of mass. That said, the power is just another "slider" in the game, and we sometimes adjust that power (2.4, 2.5, 2.6546...) to tune difficulty.

2. You're right that the forces aren't always dual. It's unfortunate, but in some cases it was necessary for gameplay and long-term system stability. That said, I think the compromises we made kept the loss of realism to a minimum.

In Warped Chaos levels, Attractors repel each other and attract everything else according to the basic law G*mass1*mass2/r^2. (We adjust G per level as one of our difficulty sliders.) Everything here is dual and balanced. Since it's fuzzy whether we're dealing with gravity or magnets, it's not so "unrealistic" to have Attractors repel.

Epicycles: this is where we had to make the biggest concessions.
- The central Attractor exerts a force on the side Attractors, but is not moved by them. Under the hood, the central attractor is simply fixed in place, so while there are forces applied, it doesn't move. In our solar system, there's a similar effect since the Sun is so massive compared to any other body, but in the game we needed to scale things to be playable on a human-sized screen!
- Side attractors do not affect each other, otherwise they would degrade each others' orbits. In our solar system, planets are so far apart these interplanetray forces are negligible. (And where it isn't, specific configurations can still be stable. Check out this info on "orbital resonance" http://en.wikipedia.org/wiki/Orbital_resonance) But in our case, we needed to fit an entire solar system on the screen without planets being nearly invisible points.
- Attractors attract simple motes, but not the other way around. This was necessary to keep side Attractors stable. In our solar system, planets are generally orders of magnitude larger than their moons/satellites, so the dual effect is minor. (Again, excepting orbital resonance configurations.) I wish we hadn't had to make this concession, as it does affect "realistic" gameplay when a player approaches a side Attractor. Ideally, approaching from "behind" to absorb the Attractor should be fine, since the momentum gained during the approach should be balanced out by the momentum change in the Attractor. But this isn't the case. Instead, since it isn't dual, you speed up during the approach, and once the Attractor is absorbed, you're likely to shoot out of the system and hit the red wall. :( You can get around this by firing some mass into the Attractor just before hitting it. It'll slow you down, and you'll get the mass back anyways. Not very realistic, but it works. Or you can approach the side Attractor from the front, which I find easier, as at least you aren't thrown out of the system.

Physics is fun! :)

Cheers,
Eddy

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Joined: Tue Nov 16, 2010 4:40 am

Re: Area or volume?

Postby Atom » Thu Nov 18, 2010 4:27 am

I made a mistake in gravity law :D
Thanks for the long answer, Eddy. I think you guys in Hemisphere made good decisions. :)

Cheers,
Atom


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