rtcrshr-camera.js

const vec3 = require('gl-vec3')

const camera = require('rtcrshr')({
  vars: {
    eye: [100, 0, 0],
    up: [0, 1, 0],
    right: [0, 0, 1],
    center: [0, 0, 0]
  },

  props: [
    'distance',
    'mouseX',
    'mouseY',
    'stiffness'
  ],

  rules: [
    { // distance constraint
      input: [ 'distance', 'eye', 'center' ],
      output: 'eye',
      rule ([ distance, inEye, inCenter ], [ outEye ]) {
        vec3.sub(outEye, inEye, inCenter)
        const s = distance / vec3.length(outEye)
        vec3.scaleAndAdd(outEye, inCenter, outEye, s)
      }
    },
    { // up/right vector orthogonality constraint
      input: [ 'up', 'eye', 'center' ],
      output: [ 'up', 'right' ],
      rule ([ inUp, inEye, inCenter ], [ outUp, outRight ]) {
        // let ec = normalize(inEye - inCenter)
        // then orthogonalize outUp = inUp - ec * dot(inUp, ec)
        // and set outRight = normalize(outUp x ec)
      }
    },
    { // mouse movement
      input: [ 'mouseX', 'mouseY', 'up', 'right', 'eye' ],
      output: [ 'eye' ],
      rule ([ mouseX, mouseY, inUp, inRight, inEye ], [ outEye ]) {
        for (let i = 0; i < 3; ++i) {
          outEye[i] = inEye[i] + mouseX * inRight[i] + mouseY * inUp[i]
        }
      }
    },
    { // momentum
      input: [ 'stiffness', 'eye', { delay: 1, var: 'eye' } ],
      output: [ 'eye' ],
      rule ([ stiffness, inEye0, inEye1 ], [ outEye ]) {
        for (let i = 0; i < 3; ++i) {
          outEye[i] = (1 - stiffness) * (inEye0[i] - inEye0[i]) + inEye0[i]
        }
      }
    }
  ]
})