scene
sceneobjects

images/textures/animated sprites
sounds

camera
lights
bounding box


direction/angle

animation & easing functions

sphere collision
bounds collision

function abs(a) {
   return Math.abs(a);
}

function length(a) { 
   return Math.sqrt(a.x*a.x + a.y*a.y + a.z*a.z); 
}

function distance(a, b) { 
   return Math.sqrt((a.x - b.x) * (a.x - b.x) +
                    (a.y - b.y) * (a.y - b.y) +
                    (a.z - b.z) * (a.z - b.z));
}

var p1 = {
	x: 20,
	y: 20
};

var p2 = {
	x: 40,
	y: 40
};

// angle in radians
var angleRadians = Math.atan2(p2.y - p1.y, p2.x - p1.x);

// angle in degrees
var angleDeg = Math.atan2(p2.y - p1.y, p2.x - p1.x) * 180 / Math.PI;

// http://onedayitwillmake.com/blog/2011/09/getting-the-angle-between-two-3d-points/

function() {
  // Make up two vectors
  var vectorA = new Vector3(5, -20, -14);
  var vectorB = new Vector3(-1, 3, 2);
 
  // Store some information about them for below
  var dot = vectorA.dot(vectorB);
  var lengthA = vectorA.length();
  var lengthB = vectorB.length();
 
  // Now to find the angle
  var theta = Math.acos( dot / (lengthA * lengthB) ); // Theta = 3.06 radians or 175.87 degrees
  // But what can you do with it?
}


function now() {
   return (new Date()).getTime() / 1000.0;
}

/// Check intersections / collisions
/// https://developer.mozilla.org/en-US/docs/Games/Techniques/3D_collision_detection

function isPointInsideAABB(point, box) {
  return (point.x >= box.minX && point.x <= box.maxX) && (point.y >= box.minY && point.y <= box.maxY) && (point.z >= box.minY && point.z <= box.maxZ);
}

function intersectCubes(a, b) {
  return (a.minX <= b.maxX && a.maxX >= b.minX) &&
         (a.minY <= b.maxY && a.maxY >= b.minY) &&
         (a.minZ <= b.maxZ && a.maxZ >= b.minZ);
}

function intersectSpheres(a, b) {
  // we are using multiplications because it's faster than calling Math.pow
  var distance = Math.sqrt((a.x - b.x) * (a.x - b.x) +
                           (a.y - b.y) * (a.y - b.y) +
                           (a.z - b.z) * (a.z - b.z));
  return distance < (a.radius + b.radius);
}

function intersectSphereBox(sphere, box) {
  // get box closest point to sphere center by clamping
  var x = Math.max(box.minX, Math.min(sphere.x, box.maxX);
  var y = Math.max(box.minY, Math.min(sphere.y, box.maxY);
  var z = Math.max(box.minZ, Math.min(sphere.z, box.maxZ);

  // this is the same as isPointInsideSphere
  var distance = Math.sqrt((x - sphere.x) * (x - sphere.x) +
                           (y - sphere.y) * (y - sphere.y) +
                           (z - sphere.z) * (z - sphere.z));
  
  return distance < sphere.radius; 
} 

function doStep(factor) { 
    objects.forEach(function(object) { 
        object.prevPosition = object.position; 
        if (object.velocity) 
            object.position += (factor * object.velocity); 
        if (object.acceleration) 
            object.velocity += (factor * object.acceleration); 
        if (object.friction) 
            object.velocity -= (factor * object.friction); 
        object.collisionCheck(); 
    }; 
} 

var speed = 1; 
var prevTime = null; 
function step(timestamp) { 
    if (!prevTime) { prevTime = now(); } 
    var elapsed = now() - prevTime; 
    factor = elapsed * speed; 
    if (factor > 0) {
     doStep(factor);
    }
    window.requestAnimationFrame(step);
}

window.requestAnimationFrame(step);