Easy way to do gravity in a simple game?

Question

I'm looking for an easy, beginner friendly way to do gravity in a platformer. I've looked into Box2D tutorials, but they all seem very complicated.

All I want is a class that takes into account if my player is grounded, or airborn, and a nice little curve as he jumps. I know this shouldn't be more than a few lines of code, and learning a library seems excessive.

Anyone mind helping me out?

Answer 1

So, implementing gravity has some prerequisites. A big one is a time keeping system. One good read for time systems is Fix Your Timestep! by gafferongames.com. The time system ties in tightly to the update loop. See deWITTERS Gameloop for info on implementing an update loop (which covers time step too). Once you have an update loop with a delta time for each iteration, you're pretty much ready.

So, you main game will have something like:

update() {
    deltaTime = getCurrentTime() - runningTime; //deltaTime is called "frameTime" too
    runningTime = getCurrentTime();

    mainCharacter.update(deltaTime);
}

and inside that main character update method it'll be like:

update(float deltaTimeInMS) {

    if (onSolidGround())
        gravity = 0;
    else 
        gravity = GLOBAL_GRAVITY; //note that global gravity is negative

    velocity.y += gravity * deltaTimeInMS;
}

Now this is a pretty basic way of doing it, and it'll be passable for simple games. I wouldn't recommend it for larger scale games however.