fix(events): use the standard wheel event (#208)

This event is now supported by all the browsers we care about. There's no need anymore to listen to the legacy events.

lib/network/modules/Canvas.js

@@ -249,8 +249,7 @@ class Canvas {
     this.hammer.on('pinch',     (event) => {this.body.eventListeners.onPinch(event)});
 
     // TODO: neatly cleanup these handlers when re-creating the Canvas, IF these are done with hammer, event.stopPropagation will not work?
-    this.frame.canvas.addEventListener('mousewheel',     (event) => {this.body.eventListeners.onMouseWheel(event)});
-    this.frame.canvas.addEventListener('DOMMouseScroll', (event) => {this.body.eventListeners.onMouseWheel(event)});
+    this.frame.canvas.addEventListener('wheel', (event) => {this.body.eventListeners.onMouseWheel(event)});
 
     this.frame.canvas.addEventListener('mousemove', (event) => {this.body.eventListeners.onMouseMove(event)});
     this.frame.canvas.addEventListener('contextmenu', (event) => {this.body.eventListeners.onContext(event)});

lib/network/modules/InteractionHandler.js

@@ -503,29 +503,14 @@ class InteractionHandler {
    */
   onMouseWheel(event) {
     if (this.options.zoomView === true) {
-      // retrieve delta
-      let delta = 0;
-      if (event.wheelDelta) { /* IE/Opera. */
-        delta = event.wheelDelta / 120;
-      }
-      else if (event.detail) { /* Mozilla case. */
-        // In Mozilla, sign of delta is different than in IE.
-        // Also, delta is multiple of 3.
-        delta = -event.detail / 3;
-      }
-
       // If delta is nonzero, handle it.
       // Basically, delta is now positive if wheel was scrolled up,
       // and negative, if wheel was scrolled down.
-      if (delta !== 0) {
+      if (event.deltaY !== 0) {
 
         // calculate the new scale
         let scale = this.body.view.scale;
-        let zoom = delta * (this.options.zoomSpeed / 10);
-        if (delta < 0) {
-          zoom = zoom / (1 - zoom);
-        }
-        scale *= (1 + zoom);
+        scale *= 1 + (event.deltaY < 0 ? 1 : -1) * (this.options.zoomSpeed * 0.1);
 
         // calculate the pointer location
         let pointer = this.getPointer({x: event.clientX, y: event.clientY});