add camera as a utility file

src/util/camera.js

@@ -0,0 +1,70 @@
+var createCamera = require('orbit-camera')
+var createScroll = require('scroll-speed')
+var mp = require('mouse-position')
+var mb = require('mouse-pressed')
+var key = require('key-pressed')
+
+const panSpeed = 0.4
+const scaleSpeed = 0.5
+const scaleMax = 3
+const scaleMin = 1.15
+
+function attachCamera(canvas, opts) {
+  opts = opts || {}
+  opts.pan = opts.pan !== false
+  opts.scale = opts.scale !== false
+  opts.rotate = opts.rotate !== false
+
+  var scroll = createScroll(canvas, opts.scale)
+  var mbut = mb(canvas, opts.rotate)
+  var mpos = mp(canvas)
+  var camera = createCamera(
+      [0, 0, 1]
+    , [0, 0, -1]
+    , [0, 1, 0]
+  )
+
+  camera.tick = tick
+
+  return camera
+
+  function tick() {
+    var ctrl = key('<control>') || key('<alt>')
+    var alt = key('<shift>')
+    var height = canvas.height
+    var width = canvas.width
+
+    if (opts.rotate && mbut.left && ctrl && !alt) {
+      camera.rotate(
+          [ mpos.x / width - 0.5, mpos.y / height - 0.5 ]
+        , [ mpos.prevX / width - 0.5, mpos.prevY / height - 0.5 ]
+      )
+    }
+
+    if (opts.pan && mbut.right || (mbut.left && !ctrl && !alt)) {
+      camera.pan([
+          (panSpeed * (mpos[0] - mpos.prev[0]) / width) * Math.pow(camera.distance, 1)
+        , (panSpeed * (mpos[1] - mpos.prev[1]) / height) * Math.pow(camera.distance, 1)
+      ])
+    }
+
+    if (opts.scale && scroll[1]) {
+      camera.distance *= Math.exp(scroll[1] * scaleSpeed / height)
+    }
+
+    if (opts.scale && (mbut.middle || (mbut.left && !ctrl && alt))) {
+      var d = (mpos.y - mpos.prevY)
+      if (!d) return;
+
+      camera.distance *= Math.exp(d / height)
+    }
+
+    if (camera.distance > scaleMax) camera.distance = scaleMax
+    if (camera.distance < scaleMin) camera.distance = scaleMin
+
+    scroll.flush()
+    mpos.flush()
+  }
+}
+
+export default attachCamera;