axis3d/camera/look-at.js

'use strict';

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.lookAt = lookAt;

var _glVec = require('gl-vec3');

var _glVec2 = _interopRequireDefault(_glVec);

function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }

var kEpsilon = 0.000000001;

// adapted from:
// https://github.com/Jam3/perspective-camera/blob/master/lib/camera-look-at.js
function lookAt(direction, target, position, up) {
  var tmp = [];
  _glVec2.default.subtract(tmp, target, position);
  _glVec2.default.normalize(tmp, tmp);
  if (tmp.every(Boolean)) {
    // not zero vector
    var d = _glVec2.default.dot(tmp, up);
    if (Math.abs(d - 1) < kEpsilon) {
      // collinear
      _glVec2.default.scale(up, direction, -1);
    } else if (Math.abs(d + 1) < kEpsilon) {
      // collinear opposite
      _glVec2.default.copy(up, direction);
    }
    _glVec2.default.copy(direction, tmp);
    _glVec2.default.cross(tmp, direction, up);
    _glVec2.default.normalize(tmp, tmp);
    _glVec2.default.cross(up, tmp, direction);
    _glVec2.default.normalize(up, up);
  }
}
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