vec2-gap

gl-matrix compatible vec2 functions that haven't been accepted yet

gl-matrix is a fantastic library for vector and matrix operations, but there are some modules I use regularly that may never be accepted into the library:

• midpoint get the point between 2 point
• perpendicular-component get the component of vector perpendicular to a unit basis vector
• set-length set an arbitrary length of a 2d vector
• truncate ensure that a 2d vector is not longer than a given length

midpoint

get the mid point between 2 points

const center = vec2.create()
midpoint(center, p0, p1) // center === midpoint between p0 and p1

perpendicular-component

determine the component of a source vector that is perpendicular to another vector (basis)

TODO: a digram here would really help clarify what this function does

// basis must be a unit vector
const basis = vec2.create(1, 0)

const source = vec2.create(50, 32)

const perp = vec2.create()

// find the portion of "source" that is perpendicular to "basis"
perpendicularComponent(perp, basis, source)

set-length

Set the exact length of a vector:

const v = vec2.create(2, 0)

const elongated = vec2.create()
setLength(elongated, v, 5) // elongated === [ 5, 0 ]

truncate

Limit the length of a vector when it exceeds a specific value

const v = vec2.create(2, 0)

const truncated = vec2.create()
truncate(truncated, v, 1.5) // vec2.length(truncated) === 1.5

// has no effect, because  vec2.length(truncated) is 1.5, which is less than 2.0
trucate(truncated, truncate, 2.0)

get-cardinal-direction

determine what cardinal direction the target is in relative to a source position. (north of, west of, northeast of, etc.)

const source = [ 0, 0]
const resolution = 4

// prints "north" because [0, -100] is north of the source
console.log(getCardinalDirection([ 0, -100 ], source, resolution)

console.log(getCardinalDirection([ 0, 100 ], source, resolution)  // prints "south"
console.log(getCardinalDirection([ 100, 0 ], source, resolution)  // prints "east"
console.log(getCardinalDirection([ -100, 0 ], source, resolution)  // prints "west"

resolution should be 4 or 8, which corresponds to [ 'north', 'east', 'south', 'west' ] and [ southeast', south', 'southwest', 'west', 'northwest', 'north', 'northeast', 'northeast' ] depending on how fine-grained of a result you want.