code simplification and impro^Cments on toggleFlip function

src/navigator.js

@@ -276,8 +276,8 @@ $.extend( $.Navigator.prototype, $.EventSource.prototype, $.Viewer.prototype, /*
     /**
       /* Flip navigator element
       */
-    toggleFlip: function() {
+    setFlip: function() {
-      this.viewport.flipped = !this.viewport.flipped;
+      this.viewport.toggleFlip();
 
       this.setDisplayTransform(this.viewer.viewport.flipped ? "scale(-1,1)" : "scale(1,1)");
       this.viewport.viewer.forceRedraw();

src/openseadragon.js

@@ -206,6 +206,9 @@
   * @property {Number} [degrees=0]
   *     Initial rotation.
   *
+  * @property {Boolean} [flip=false]
+  *     Initial flip state.
+  *
   * @property {Number} [minZoomLevel=null]
   *
   * @property {Number} [maxZoomLevel=null]

src/viewer.js

@@ -367,6 +367,7 @@ $.Viewer = function( options ) {
         maxZoomLevel:       this.maxZoomLevel,
         viewer:             this,
         degrees:            this.degrees,
+        flipped:            this.flipped,
         navigatorRotate:    this.navigatorRotate,
         homeFillsViewer:    this.homeFillsViewer,
         margins:            this.viewportMargins

src/viewport.js

@@ -1525,12 +1525,19 @@ $.Viewport.prototype = {
      * Toggle flip state and demands a new drawing on navigator and viewer objects.
     */
     toggleFlip: function() {
-      this.flipped = !this.flipped;
+      this.setFlip(!this.getFlip());
       if(this.viewer.navigator){
-        this.viewer.navigator.toggleFlip();
+        this.viewer.navigator.setFlip();
       }
-      this.viewer._forceRedraw = !this.viewer._forceRedraw;
       this.viewer.forceRedraw();
+    },
+
+    getFlip: function() {
+      return this.flipped;
+    },
+
+    setFlip: function( state ) {
+      this.flipped = state;
     }
 
 };