Merge pull request #754 from fs-webdev/master

Added a patch to help slow down the scroll devices that fire too fast…

src/openseadragon.js

@@ -255,6 +255,11 @@
   * @property {Boolean} [preserveImageSizeOnResize=false]
   *     Set to true to have the image size preserved when the viewer is resized. This requires autoResize=true (default).
   *
+  * @property {Number} [minScrollDeltaTime=50]
+  *     Number of milliseconds between canvas-scroll events. This value helps normalize the rate of canvas-scroll
+  *     events between different devices, causing the faster devices to slow down enough to make the zoom control
+  *     more manageable.
+  *
   * @property {Number} [pixelsPerWheelLine=40]
   *     For pixel-resolution scrolling devices, the number of pixels equal to one scroll line.
   *
@@ -1003,6 +1008,7 @@ if (typeof define === 'function' && define.amd) {
             pixelsPerWheelLine:     40,
             autoResize:             true,
             preserveImageSizeOnResize: false, // requires autoResize=true
+            minScrollDeltaTime:     50,
 
             //DEFAULT CONTROL SETTINGS
             showSequenceControl:     true,  //SEQUENCE

src/viewer.js

@@ -203,6 +203,8 @@ $.Viewer = function( options ) {
     this._loadQueue = [];
     this.currentOverlays = [];
 
+    this._lastScrollTime = $.now(); // variable used to help normalize the scroll event speed of different devices
+
     //Inherit some behaviors and properties
     $.EventSource.call( this );
 
@@ -2738,7 +2740,17 @@ function onCanvasPinch( event ) {
 
 function onCanvasScroll( event ) {
     var gestureSettings,
-        factor;
+        factor,
+        thisScrollTime,
+        deltaScrollTime;
+
+    /* Certain scroll devices fire the scroll event way too fast so we are injecting a simple adjustment to keep things
+     * partially normalized. If we have already fired an event within the last 'minScrollDelta' milliseconds we skip
+     * this one and wait for the next event. */
+    thisScrollTime = $.now();
+    deltaScrollTime = thisScrollTime - this._lastScrollTime;
+    if (deltaScrollTime > this.minScrollDeltaTime) {
+        this._lastScrollTime = thisScrollTime;
 
         if ( !event.preventDefaultAction && this.viewport ) {
             gestureSettings = this.gestureSettingsByDeviceType( event.pointerType );
@@ -2772,12 +2784,15 @@ function onCanvasScroll( event ) {
             shift: event.shift,
             originalEvent: event.originalEvent
         });
-
         if (gestureSettings && gestureSettings.scrollToZoom) {
             //cancels event
             return false;
         }
     }
+    else {
+        return false;   // We are swallowing this event
+    }
+}
 
 function onContainerEnter( event ) {
     THIS[ this.hash ].mouseInside = true;