configurable manual zoom speed (#3657)

docs/network/interaction.html

@@ -70,7 +70,8 @@ var options = {
     selectable: true,
     selectConnectedEdges: true,
     tooltipDelay: 300,
-    zoomView: true
+    zoomView: true,
+    zoomSpeed: 1
   }
 }
 
@@ -109,6 +110,7 @@ network.setOptions(options);
         <tr><td>selectConnectedEdges</td>   <td>Boolean</td><td><code>true</code></td><td>When true, on selecting a node, its connecting edges are highlighted.</td></tr>
         <tr><td>tooltipDelay</td>           <td>Number</td>             <td><code>300</code></td>        <td>When nodes or edges have a defined <code>'title'</code> field, this can be shown as a pop-up tooltip. The tooltip itself is an HTML element that can be fully styled using CSS. The delay is the amount of time in milliseconds it takes before the tooltip is shown.</td></tr>
         <tr><td>zoomView</td>               <td>Boolean</td>            <td><code>true</code></td>      <td>When true, the user can zoom in.</td></tr>
+        <tr><td>zoomSpeed</td>              <td>Number</td>             <td><code>1</code></td>         <td>The default speed of "1" (arbitrary unit) is moderately fast. Speed changes apply only to manual zooming (e.g. with mouse scroll wheel).</td></tr>
     </table>
 
 </div>

lib/network/modules/InteractionHandler.js

@@ -53,7 +53,8 @@ class InteractionHandler {
       },
       navigationButtons: false,
       tooltipDelay: 300,
-      zoomView: true
+      zoomView: true,
+      zoomSpeed: 1
     };
     util.extend(this.options,this.defaultOptions);
 
@@ -520,7 +521,7 @@ class InteractionHandler {
 
         // calculate the new scale
         let scale = this.body.view.scale;
-        let zoom = delta / 10;
+        let zoom = delta * (this.options.zoomSpeed / 10);
         if (delta < 0) {
           zoom = zoom / (1 - zoom);
         }

lib/network/options.js

@@ -167,6 +167,7 @@ let allOptions = {
     hoverConnectedEdges: { boolean: bool },
     tooltipDelay: { number },
     zoomView: { boolean: bool },
+    zoomSpeed: { number },
     __type__: { object }
   },
   layout: {
@@ -572,7 +573,8 @@ let configureOptions = {
     selectConnectedEdges: true,
     hoverConnectedEdges: true,
     tooltipDelay: [300, 0, 1000, 25],
-    zoomView: true
+    zoomView: true,
+    zoomSpeed: 1
   },
   manipulation: {
     enabled: false,