Quote:Original post by aeroz
Hello,
I'm currently developing a simple side-scrolling game in outer space. You control an astronaut and you have to collect all sorts of things. [grin]
The blocks you can stand on are not like in the old "Super Mario" games but they can also be irregular polygons. (tilted ground) I want some simple physics in the game.

There are games that are usable because they adhere to traditional and "fun" unrealistic conventions (e.g. standing unbalanced on the last pixel of a platform in a platformer) and games that are usable because they adhere to physical intuition (e.g. unlimited-speed Asteroids); with "some simple physics" you risk to fall in the middle, with an impractical simulation that is too complex and quirky to be realistic and too strange and unpredictable to be conventional.

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I want the player to be always straight up.

In outer space there is no "straight up". I think you really want to align the astronaut with the screen, and perhaps keep him completely or partially centered, for user interface reasons; but you can let him move naturally and rotate and translate the viewport to place him as desired, instead of hacking the physical model and opening the door to worse problems.

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Should I create the player's body and shape and set the rotational inertia to 0? Then nothing can tilt the player over. What if I want the player to rotate when for example a bomb explodes and throws him into the air? Maybe I can set the rotational inertia back to a positive number? Or should I always have the player with an inertia not equal to 0 and write a function that balances the player on the ground?

You can use a correct inertia moment and apply (with the mentioned jetpack and other very visible means) torques and forces that compensates unwanted pushing, when the astronaut wants and with appropriate limitations and quirks. Small nozzles on the shoulders, pointing straight forward and straight back, should be good-looking and physically sensible (as far as possible from the center of mass while still on the astronaut's torso).

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What I would really like is when you are able to rotate the player while you are in the air (with your jet pack) but not on the ground. You can press keys to rotate the player and another to accelerate him in the direction he is facing.

A straightforward control scheme, but does the jetpack point up or forward? Is there any gravity or fake gravity? And most importantly, what happens "on the ground"?
My first choice would be a jetpack pointing up, that always propels the astronaut where his head points (up arrow), and left/right arrows that make the astronaut walk when his feet are in contact with a surface (easily deduced by the reported contact points), regardless of gravity (he can have magnetic boots), and make him turn when he's flying or falling (at a fixed speed, firing a propulsor briefly when the key is pressed and the contrary one while the key is released; this translates into applying a torque to accelerate and to decelerate for a few simulation frames, with constant angular speed in the middle).

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But what if you land on the ground upside down? The game has to apply a torque that it turns back? (stand up)

Predict the time to impact and automatically turn him with his thrusters. You might get away without adding animations for staggering and for standing up from prone and supine positions.

You can use a physics system like Box2D in a sidescroller. It can be a bit of a pain setting things up correctly, but its certainly doable.