create-orbit-camera/src/matrix-math/make-look-at.js

Create a camera that orbits a target

module.exports = MakeLookAt

function MakeLookAt (cameraPosition, target, up) {
  var zAxis = normalize(subtractVectors(cameraPosition, target))
  var xAxis = cross(up, zAxis)
  var yAxis = cross(zAxis, xAxis)

  return [
    xAxis[0], xAxis[1], xAxis[2], 0,
    yAxis[0], yAxis[1], yAxis[2], 0,
    zAxis[0], zAxis[1], zAxis[2], 0,
    cameraPosition[0],
    cameraPosition[1],
    cameraPosition[2],
    1
  ]
}

function normalize (v) {
  var length = Math.sqrt(v[0] * v[0] + v[1] * v[1] + v[2] * v[2])
  // make sure we don't divide by 0.
  if (length > 0.00001) {
    return [v[0] / length, v[1] / length, v[2] / length]
  } else {
    return [0, 0, 0]
  }
}

function subtractVectors (a, b) {
  return [a[0] - b[0], a[1] - b[1], a[2] - b[2]]
}

function cross (a, b) {
  return [a[1] * b[2] - a[2] * b[1],
    a[2] * b[0] - a[0] * b[2],
    a[0] * b[1] - a[1] * b[0]]
}