Question

I need help/advice for improving/commenting my current design please 🙂

This relates to collision detection in a simple game: Dynamic bodies (moving ones) might collide with static bodies (i.e. ground, walls). I’m porting my Obj-C model to Javascript and am facing memory/performance questions as to my way of implementing this.

I’m using a very basic approach: An array of arrays represents my level in terms of physic opacity.

• bit set to 0: Transparent area, bodies can go through

• bit set to 1: Opaque area, bodies collide

Testing the transparency/opacity of a pixel simply goes as follows:

if (grid[x][y]) {
 // collide!
}

My knowledge of JS is pretty limited in termes of performance/memory and can’t evaluate how good this approach is 🙂 No idea of the efficiency of using arrays that being said.

Just imagine a 1000-pixel wide level that’s 600px high. It’s a small level but this already means an array containing 1000 arrays each containing up to 600 entries. Besides, I’ve not found a way to ensure I create a 1bit-sized element like low-level languages have.

Using the following, can I be sure an entry isn’t something “else” than a bit?

grid[x][y] = true;
grid[x][y] = false;

Thanks for your time and comments/advices!

J.

Answer 1

If you have an 1000×600 grid, you can guarantee you have at least 601 arrays in memory (1001 if you do it the other way round).

Rather than doing this, I would consider using either 1 array, or (preferrably) one object with a mapping scheme.

var map = {};
map["1x1"] = 1;
map["1x3"] = 1;
// assume no-hits are empty and free to move through

function canGoIn(x, y) {
    return map.hasOwnProperty(x + "x" + y);
};

Alternately;

var map = [];
var width = 600;
map.push(0);
map.push(1);
// etc

function canGoIn(x, y) {
    return map[(x * width) + y] == 1;
}