Hey Forum Dudes/Chicks, I was wondering if anyone could show me how to implement gravity into a 2-D game so that I can make the main character jump. I assume this question has been asked many times, so if there is a previous forum post with sufficient information on this subject, that will do just fine. Thanks in advance!

Also, if I need to attach code to allow you to further help me, I will gladly do so!

-Egghead

I'd say, just use real world formulas and make a simple physics engine of your own.
You need to implement the following: velocity vector - how much position of a character changes per tick; acceleration vector - how much velocity changes per second; force - thing, that constantly causes acceleration, measured in newtons (each newton causes 1 m/s2 acceleration for a body with a mass of 1 kg) so you could:

  ApplyForce(character,directionDownVector,9.8);

And now you have gravity. Gravity acceleration should stop on collision with ground.
Then you need to implement impulse: impulse is like force but only causes acceleration once.
So, to jump a character, you would, say:

  ApplyImpulse(character,directionUpVector,100);

Thanks a ton for the help everyone, I looked a little bit more into actual physics equations and values and got a sort of primitive gravity system working on a single object in Allegro, which is exactly what I was looking for! I greatly appreciate your responses to my question.;D

You guys make it all look so complicated... Just subtract some small constant from the y speed each loop, allowing for collision with the ground or something to stop his fall.

You might want to look into Chipmunk2D, http://chipmunk-physics.net/

It's a 2D physics engine that'll do gravity, friction, collisions etc.

I though OP already figured out how to do what he wanted...

It doesn't really matter if you already solved your problem, we can still discuss about this topic, remember, we are at allegro.cc, where you never know when a thread will die

Can you post the equations you used? I'm sure those have to be equivalent to the one I posted.

I'm talking about projectile motion, this is the motion we need in order to model a jumping character, just like Mario, you need a formula like the one I posted, unless you went beyond Newtonian physics and discovered some new formulas (which I really doubt)

{"name":"projectile-motion.gif","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/9\/7\/977ced46f0dbc932118e4e65ccb1a236.gif","w":387,"h":281,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/9\/7\/977ced46f0dbc932118e4e65ccb1a236"}

Yes indeed, no need for such formulas.
They aren't even very useful for games, since they take time as an argument while you want your physics to be step based in almost every circumstance.

object.velocity += world.gravity * object.drag; (with drag 0 < drag < 1 lower = more)
Now you've got gravity + an extremely simplified drag model, terminal velocity and slowing down, can also be used for friction.

(I tend to simply use simple if statements to limit the maximum velocity in any direction instead of the above)