Gravity(Once Again)

[Dr.Linux]

A while back i put a topic asking on how to make gravity in a platformer game. Now I want to know how to do it without a library, engine or framework. Thanks in Advance!

[harrywatson]

If you are using javascript and canvas ?

var canvas = document.getElementById('canvas'),context = canvas.getContext('2d'),Gravity = 9.81,height = 10 ;                                      //ten will be the height of your game Character.y = 0 + Gravity / height;

Hmm just off the top of my head this might work. I haven't tried it. You could have a look where I simplified it from here....

 

http://corehtml5canvas.com/code-live/ch07/example-7.1/example.html

 

Also I believe it could be very easy to apply gravity to the whole scene and create exceptions, this is in a framework

but the code is not reliant on that framework.....

var i = 0; var speed1 = 0.5, speed2 = 0.3; z1.y += speed1;    //z1 and z2 are zombies subject to gravity z2.y += speed2;

Well that's my own attempt at gravity which works well, hope you can get something from this

 

Harry

[alex_h]

At it's heart the issue is really as simple as having an update loop on the game object to which gravity should be applied, that... well, applies gravity :

var gravity = <some positive value>;//var speed = <whatever>;//horizontal movement stepthis.update = function(deltaTime){    //********************************************    //VERTICAL velocity    //********************************************    this.velocity.y += gravity;    //********************************************    //HORIZONTAL VELOCITY    //********************************************    this.velocity.x = speed;    //********************************************    //update position    //********************************************    this.position.y += this.velocity.y * deltaTime;    this.position.x += this.velocity.x * deltaTime;    //************************************}

After doing this each frame you then collision check against any nearby platforms and correct if an overlap was detected.

 

Then you apply the x and y from the position point to your display objects transform properties.

 

Make the player jump by setting the velocity.y to a negative number, something like gravity times minus 10, depending on how high you want them to jump. This is roughly equivalent to applying an impulse to a body in a physics engine.

[Dr.Linux]

Thanks! It was a lot easier than I thought.