Merge pull request #1937 from ronnymikalsen/1763-a11y-browser-zoom

fix(a11y): draw the level based on pixel density ratio

src/openseadragon.js

@@ -986,7 +986,7 @@ function OpenSeadragon( options ){
      * @member {Number} pixelDensityRatio
      * @memberof OpenSeadragon
      */
-    $.pixelDensityRatio = (function () {
+    $.getCurrentPixelDensityRatio = function() {
         if ( $.supportsCanvas ) {
             var context = document.createElement('canvas').getContext('2d');
             var devicePixelRatio = window.devicePixelRatio || 1;
@@ -999,7 +999,13 @@ function OpenSeadragon( options ){
         } else {
             return 1;
         }
-    }());
+    };
+
+    /**
+     * @member {Number} pixelDensityRatio
+     * @memberof OpenSeadragon
+     */
+    $.pixelDensityRatio = $.getCurrentPixelDensityRatio();
 
 }( OpenSeadragon ));
 

src/tilesource.js

@@ -313,8 +313,8 @@ $.TileSource.prototype = {
      */
     getPixelRatio: function( level ) {
         var imageSizeScaled = this.dimensions.times( this.getLevelScale( level ) ),
-            rx = 1.0 / imageSizeScaled.x,
+            rx = 1.0 / imageSizeScaled.x * $.pixelDensityRatio,
-            ry = 1.0 / imageSizeScaled.y;
+            ry = 1.0 / imageSizeScaled.y * $.pixelDensityRatio;
 
         return new $.Point(rx, ry);
     },

src/viewer.js

@@ -220,6 +220,7 @@ $.Viewer = function( options ) {
     this._updateRequestId = null;
     this._loadQueue = [];
     this.currentOverlays = [];
+    this._updatePixelDensityRatioBind = null;
 
     this._lastScrollTime = $.now(); // variable used to help normalize the scroll event speed of different devices
 
@@ -426,6 +427,8 @@ $.Viewer = function( options ) {
         }
     }
 
+    this._addUpdatePixelDensityRatioEvent();
+
     //Instantiate a navigator if configured
     if ( this.showNavigator){
         this.navigator = new $.Navigator({
@@ -748,6 +751,8 @@ $.extend( $.Viewer.prototype, $.EventSource.prototype, $.ControlDock.prototype,
             return;
         }
 
+        this._removeUpdatePixelDensityRatioEvent();
+
         this.close();
 
         this.clearOverlays();
@@ -2268,6 +2273,38 @@ $.extend( $.Viewer.prototype, $.EventSource.prototype, $.ControlDock.prototype,
         } else {
             $.console.warn('Attempting to display a reference strip while "sequenceMode" is off.');
         }
+    },
+
+    /**
+     * Adds _updatePixelDensityRatio to the window resize event.
+     * @private
+     */
+    _addUpdatePixelDensityRatioEvent: function() {
+        this._updatePixelDensityRatioBind = this._updatePixelDensityRatio.bind(this);
+        $.addEvent( window, 'resize', this._updatePixelDensityRatioBind );
+    },
+
+    /**
+     * Removes _updatePixelDensityRatio from the window resize event.
+     * @private
+     */
+    _removeUpdatePixelDensityRatioEvent: function() {
+        $.removeEvent( window, 'resize', this._updatePixelDensityRatioBind );
+    },
+
+    /**
+     * Update pixel density ratio, clears all tiles and triggers updates for
+     * all items if the ratio has changed.
+     * @private
+     */
+     _updatePixelDensityRatio: function() {
+        var previusPixelDensityRatio = $.pixelDensityRatio;
+        var currentPixelDensityRatio = $.getCurrentPixelDensityRatio();
+        if (previusPixelDensityRatio !== currentPixelDensityRatio) {
+            $.pixelDensityRatio = currentPixelDensityRatio;
+            this.world.resetItems();
+            this.forceRedraw();
+        }
     }
 });