var Vector = {};
These are general-purpose functions that deal with vectors - in this case, three-dimensional vectors represented as objects in the form
{ x, y, z }
Since we're not using traditional object oriented techniques, these
functions take and return that sort of logic-less object, so you'll see
add(a, b)
rather than a.add(b)
.
var Vector = {};
Vector.UP = { x: 0, y: 1, z: 0 };
Vector.ZERO = { x: 0, y: 0, z: 0 };
Vector.WHITE = { x: 255, y: 255, z: 255 };
Vector.ZEROcp = function() {
return { x: 0, y: 0, z: 0 };
};
is different than the rest of these since it takes two vectors but returns a single number value.
Vector.dotProduct = function(a, b) {
return (a.x * b.x) + (a.y * b.y) + (a.z * b.z);
};
Vector.crossProduct = function(a, b) {
return {
x: (a.y * b.z) - (a.z * b.y),
y: (a.z * b.x) - (a.x * b.z),
z: (a.x * b.y) - (a.y * b.x)
};
};
Enlongate or shrink a vector by a factor of t
Vector.scale = function(a, t) {
return {
x: a.x * t,
y: a.y * t,
z: a.z * t
};
};
Turn any vector into a vector that has a magnitude of 1.
If you consider that a unit sphere is a sphere with a radius of 1, a unit vector is like a vector from the center point (0, 0, 0) to any point on its surface.
Vector.unitVector = function(a) {
return Vector.scale(a, 1 / Vector.length(a));
};
Add two vectors to each other, by simply combining each of their components
Vector.add = function(a, b) {
return {
x: a.x + b.x,
y: a.y + b.y,
z: a.z + b.z
};
};
A version of add
that adds three vectors at the same time. While
it's possible to write a clever version of Vector.add
that takes
any number of arguments, it's not fast, so we're keeping it simple and
just making two versions.
Vector.add3 = function(a, b, c) {
return {
x: a.x + b.x + c.x,
y: a.y + b.y + c.y,
z: a.z + b.z + c.z
};
};
Subtract one vector from another, by subtracting each component
Vector.subtract = function(a, b) {
return {
x: a.x - b.x,
y: a.y - b.y,
z: a.z - b.z
};
};
Length, or magnitude, measured by Euclidean norm
Vector.length = function(a) {
return Math.sqrt(Vector.dotProduct(a, a));
};
Given a vector a
, which is a point in space, and a normal
, which is
the angle the point hits a surface, returna new vector that is reflect
off of that surface
Vector.reflectThrough = function(a, normal) {
var d = Vector.scale(normal, Vector.dotProduct(a, normal));
return Vector.subtract(Vector.scale(d, 2), a);
};