Javascript phsyics in a 2d space
- by eroo
So, I am working on teaching myself Canvas (HTML5) and have most of a simple game engine coded up. It is a 2d representation of a space scene (planets, stars, celestial bodies, etc). My default "Sprite" class has a frame listener like such:
"baseClass" contains a function that allows inheritance and applies "a" to "this.a". So, "var aTest = new Sprite({foo: 'bar'});" would make "aTest.foo = 'bar'". This is how I expose my objects to each other.
{
Sprite = baseClass.extend({
init: function(a){
baseClass.init(this, a);
this.fields = new Array(); // list of fields of gravity one is in. Not sure if this is a good idea.
this.addFL(function(tick){ // this will change to be independent of framerate soon.
// and this is where I need help
// gobjs is an array of all the Sprite objects in the "world".
for(i = 0; i < gobjs.length; i++){
// Make sure its got setup correctly, make sure it -wants- gravity, and make sure it's not -this- sprite.
if(typeof(gobjs[i].a) != undefined && !gobjs[i].a.ignoreGravity && gobjs[i].id != this.id){
// Check if it's within a certain range (obviously, gravity doesn't work this way... But I plan on having a large "space" area,
// And I can't very well have all objects accounted for at all times, can I?
if(this.distanceTo(gobjs[i]) < this.s.size*10 && gobjs[i].fields.indexOf(this.id) == -1){
gobjs[i].fields.push(this.id);
}
}
}
for(i = 0; i < this.fields.length; i++){
distance = this.distanceTo(gobjs[this.fields[i]]);
angletosun = this.angleTo(gobjs[this.fields[i]])*(180/Math.PI); // .angleTo works very well, returning the angle in radians, which I convert to degrees here.
// I have no idea what should happen here, although through trial and error (and attempting to read Maths papers on gravity (eeeeek!)), this sort of mimics gravity.
// angle is its orientation, currently I assign a constant velocity to one of my objects, and leave the other static (it ignores gravity, but still emits it).
this.a.angle = angletosun+(75+(distance*-1)/5); //todo: omg learn math
if(this.distanceTo(gobjs[this.fields[i]]) > gobjs[this.fields[i]].a.size*10)
this.fields.splice(i); // out of range, stop effecting.
}
});
}
});
}
Thanks in advance. The real trick is that one line:
{
this.a.angle = angletosun+(75+(distance*-1)/5);
}
This is more a physics question than Javascript, but I've searched and searched and read way to many wiki articles on orbital mathematics. It gets over my head very quickly.
Edit: There is a weirdness with the SO formatting; forgives me, I is noobie.
