initial attempt at cleaning up events in terms of where they are raised, how they affect default behavior, and how the affect other handlers. I need to do another pass because its clear that we want to be able to independently prevent default and stop propagation just like normal javascript events

src/drawer.js

@@ -133,25 +133,31 @@ $.Drawer.prototype = {
      * @param {OpenSeadragon.OverlayPlacement} placement - The position of the 
      *      viewport which the location coordinates will be treated as relative 
      *      to. 
+     * @return {OpenSeadragon.Drawer} Chainable.
      */
     addOverlay: function( element, location, placement ) {
+        var stop;
         element = $.getElement( element );
 
-        if ( getOverlayIndex( this.overlays, element ) >= 0 ) {
-            // they're trying to add a duplicate overlay
-            return;     
-        }
-
-        this.overlays.push( new $.Overlay( element, location, placement ) );
-        this.updateAgain = true;
         if( this.viewer ){
-            this.viewer.raiseEvent( 'add-overlay', { 
+            stop = this.viewer.raiseEvent( 'addoverlay', { 
                 viewer: this.viewer,
                 element: element, 
                 location: location, 
                 placement: placement
             });
+            if( false === stop ){
+                return this;
+            }
         }
+
+        if ( getOverlayIndex( this.overlays, element ) >= 0 ) {
+            // they're trying to add a duplicate overlay
+            return this;     
+        }
+
+        this.overlays.push( new $.Overlay( element, location, placement ) );
+        this.updateAgain = true;
         return this;
     },
 
@@ -167,22 +173,27 @@ $.Drawer.prototype = {
      * @return {OpenSeadragon.Drawer} Chainable.
      */
     updateOverlay: function( element, location, placement ) {
-        var i;
+        var i,
+            stop;
 
         element = $.getElement( element );
         i = getOverlayIndex( this.overlays, element );
 
-        if ( i >= 0 ) {
-            this.overlays[ i ].update( location, placement );
-            this.updateAgain = true;
-        }
         if( this.viewer ){
-            this.viewer.raiseEvent( 'update-overlay', { 
+            stop = this.viewer.raiseEvent( 'updateoverlay', { 
                 viewer: this.viewer,
                 element: element, 
                 location: location, 
                 placement: placement
             });
+            if( false === stop ){
+                return this;
+            }
+        }
+
+        if ( i >= 0 ) {
+            this.overlays[ i ].update( location, placement );
+            this.updateAgain = true;
         }
         return this;
     },
@@ -201,17 +212,21 @@ $.Drawer.prototype = {
         element = $.getElement( element );
         i = getOverlayIndex( this.overlays, element );
 
+        if( this.viewer ){
+            stop = this.viewer.raiseEvent( 'removeoverlay', { 
+                viewer: this.viewer,
+                element: element
+            });
+            if( false === stop ){
+                return this;
+            }
+        }
+
         if ( i >= 0 ) {
             this.overlays[ i ].destroy();
             this.overlays.splice( i, 1 );
             this.updateAgain = true;
         }
-        if( this.viewer ){
-            this.viewer.raiseEvent( 'remove-overlay', { 
-                viewer: this.viewer,
-                element: element
-            });
-        }
         return this;
     },
 
@@ -222,15 +237,19 @@ $.Drawer.prototype = {
      * @return {OpenSeadragon.Drawer} Chainable.
      */
     clearOverlays: function() {
-        while ( this.overlays.length > 0 ) {
+        var stop;
-            this.overlays.pop().destroy();
-            this.updateAgain = true;
-        }
         if( this.viewer ){
-            this.viewer.raiseEvent( 'clear-overlay', { 
+            stop = this.viewer.raiseEvent( 'clearoverlay', { 
                 viewer: this.viewer,
                 element: element
             });
+            if( false === stop ){
+                return this;
+            }
+        }
+        while ( this.overlays.length > 0 ) {
+            this.overlays.pop().destroy();
+            this.updateAgain = true;
         }
         return this;
     },
@@ -412,12 +431,6 @@ function updateViewport( drawer ) {
     
     drawer.updateAgain = false;
 
-    if( drawer.viewer ){
-        drawer.viewer.raiseEvent( 'update-viewport', { 
-            viewer: drawer.viewer
-        });
-    }
-
     var tile,
         level,
         best            = null,
@@ -571,20 +584,6 @@ function updateLevel( drawer, haveDrawn, level, levelOpacity, levelVisibility, v
         viewportCenter  = drawer.viewport.pixelFromPoint( drawer.viewport.getCenter() );
 
 
-    if( drawer.viewer ){
-        drawer.viewer.raiseEvent( 'update-level', { 
-            viewer: drawer.viewer,
-            havedrawn: haveDrawn,
-            level: level, 
-            opacity: levelOpacity,
-            visibility: levelVisibility, 
-            topleft: viewportTopLeft, 
-            bottomright: viewportBottomRight, 
-            currenttime: currentTime, 
-            best: best
-        });
-    }
-
     //OK, a new drawing so do your calculations
     tileTL    = drawer.source.getTileAtPoint( level, viewportTL );
     tileBR    = drawer.source.getTileAtPoint( level, viewportBR );
@@ -636,13 +635,6 @@ function updateTile( drawer, drawLevel, haveDrawn, x, y, level, levelOpacity, le
         drawTile = drawLevel,
         newbest;
 
-    if( drawer.viewer ){
-        drawer.viewer.raiseEvent( 'update-tile', { 
-            viewer: drawer.viewer,
-            tile: tile
-        });
-    }
-
     setCoverage( drawer.coverage, level, x, y, false );
 
     if ( !tile.exists ) {
@@ -1140,12 +1132,6 @@ function drawTiles( drawer, lastDrawn ){
             }
         }
 
-        if( drawer.viewer ){
-            drawer.viewer.raiseEvent( 'tile-drawn', { 
-                viewer: drawer.viewer,
-                tile: tile
-            });
-        }
     }
 }
 

src/eventhandler.js

@@ -81,10 +81,14 @@ $.EventHandler.prototype = {
             Array.apply( null, events );
         return function( source, args ) {
             var i, 
-                length = events.length;
+                length = events.length,
+                stop;
             for ( i = 0; i < length; i++ ) {
-                if( events[ i ] ){
+                if( $.isFunction( events[ i ] ) {
-                    events[ i ]( source, args );
+                    stop = events[ i ].apply( source, args );
+                    if( stop === false ){
+                        return stop;
+                    }
                 }
             }
         };
@@ -106,7 +110,7 @@ $.EventHandler.prototype = {
                 eventArgs = {};
             }
 
-            handler( this, eventArgs );
+            return handler( this, eventArgs );
         }
     }
 };

src/viewer.js

@@ -342,6 +342,11 @@ $.extend( $.Viewer.prototype, $.EventHandler.prototype, $.ControlDock.prototype,
             overlay,
             i;
 
+        if( false === this.raiseEvent( 'open', { source: source } ) ){
+            //cancel open
+            return this;
+        }
+
         if ( this.source ) {
             this.close( );
         }
@@ -506,8 +511,6 @@ $.extend( $.Viewer.prototype, $.EventHandler.prototype, $.ControlDock.prototype,
             this.navigator.open( source );
         }
 
-        this.raiseEvent( 'open', { source: source, viewer: this } );
-
         return this;
     },
 
@@ -517,6 +520,10 @@ $.extend( $.Viewer.prototype, $.EventHandler.prototype, $.ControlDock.prototype,
      * @return {OpenSeadragon.Viewer} Chainable.
      */
     close: function ( ) {
+        if( false === this.raiseEvent( 'close' ) ){
+            //cancel close
+            return this;
+        }
         
         if( this.drawer ){
             this.drawer.clearOverlays();
@@ -532,8 +539,6 @@ $.extend( $.Viewer.prototype, $.EventHandler.prototype, $.ControlDock.prototype,
         VIEWERS[ this.hash ] = null;
         delete VIEWERS[ this.hash ];
         
-        this.raiseEvent( 'close', { viewer: this } );
-        
         return this;
     },
 
@@ -553,8 +558,11 @@ $.extend( $.Viewer.prototype, $.EventHandler.prototype, $.ControlDock.prototype,
      * @return {OpenSeadragon.Viewer} Chainable.
      */
     setMouseNavEnabled: function( enabled ){
+        if( false === this.raiseEvent( enabled ? 'activate' : 'deactivate' ) ){
+            //cancel activation/deactivation of mouse/touch/keyboard interactive
+            return this;
+        }
         this.innerTracker.setTracking( enabled );
-        this.raiseEvent( 'mouse-enabled', { enabled: enabled, viewer: this } );
         return this;
     },
 
@@ -580,12 +588,15 @@ $.extend( $.Viewer.prototype, $.EventHandler.prototype, $.ControlDock.prototype,
      * @return {OpenSeadragon.Viewer} Chainable.
      */
     setControlsEnabled: function( enabled ) {
+        if( false === this.raiseEvent( enabled ? 'showcontrols' : 'hidecontrols' ) ){
+            //cancel show/hide of controls
+            return this;
+        }
         if( enabled ){
             abortControlsAutoHide( this );
         } else {
             beginControlsAutoHide( this );
         }
-        this.raiseEvent( 'controls-enabled', { enabled: enabled, viewer: this } );
         return this;
     },
 
@@ -622,6 +633,11 @@ $.extend( $.Viewer.prototype, $.EventHandler.prototype, $.ControlDock.prototype,
             nodes,
             i;
         
+        if( false === this.raiseEvent( fullPage ? 'maximize' : 'minimize' ) ){
+            //cancel maximize/minimize
+            return this;
+        }
+
         //dont bother modifying the DOM if we are already in full page mode.
         if ( fullPage == this.isFullPage() ) {
             return;
@@ -747,7 +763,6 @@ $.extend( $.Viewer.prototype, $.EventHandler.prototype, $.ControlDock.prototype,
             $.delegate( this, onContainerExit )();      
 
         }
-        this.raiseEvent( 'fullpage', { fullpage: fullPage, viewer: this } );
 
         if ( this.viewport ) {
             oldBounds = this.viewport.getBounds();
@@ -806,8 +821,11 @@ $.extend( $.Viewer.prototype, $.EventHandler.prototype, $.ControlDock.prototype,
      * @return {OpenSeadragon.Viewer} Chainable.
      */
     setVisible: function( visible ){
+        if( false === this.raiseEvent( visible ? 'show' : 'hide' ) ){
+            //cancel show/hide
+            return this;
+        }
         this.container.style.visibility = visible ? "" : "hidden";
-        this.raiseEvent( 'visible', { visible: visible, viewer: this } );
         return this;
     },
 
@@ -1026,9 +1044,11 @@ $.extend( $.Viewer.prototype, $.EventHandler.prototype, $.ControlDock.prototype,
      * @return {OpenSeadragon.Viewer} Chainable.
      */
     goToPage: function( page ){
-        //page is a 1 based index so normalize now
+
-        //page = page;
+        if( false === this.raiseEvent( 'page', { page: page }) ){
-        this.raiseEvent( 'page', { page: page, viewer: this } );
+            //cancel page change
+            return this;
+        }
 
         if( this.tileSources.length > page ){
             
@@ -1171,8 +1191,15 @@ function onBlur(){
 
 function onCanvasClick( tracker, position, quick, shift, event ) {
     var zoomPreClick,
-        factor;
+        factor,
-    if ( this.viewport && quick ) {    // ignore clicks where mouse moved         
+        stop = this.raiseEvent( 'click', { 
+            tracker: tracker,
+            position: position,
+            quick: quick,
+            shift: shift,
+            originalEvent: event 
+        });
+    if ( this.viewport && quick && stop !== false ) {    // ignore clicks where mouse moved         
         zoomPerClick = this.zoomPerClick;
         factor = shift ? 1.0 / zoomPerClick : zoomPerClick;
         this.viewport.zoomBy(
@@ -1181,17 +1208,17 @@ function onCanvasClick( tracker, position, quick, shift, event ) {
         );
         this.viewport.applyConstraints();
     }
-    this.raiseEvent( 'click', { 
-        tracker: tracker,
-        position: position,
-        quick: quick,
-        shift: shift,
-        originalEvent: event 
-    });
 }
 
 function onCanvasDrag( tracker, position, delta, shift, event ) {
-    if ( this.viewport ) {
+    var stop = this.raiseEvent( 'drag', { 
+        tracker: tracker,
+        position: position,
+        delta: delta,
+        shift: shift,
+        originalEvent: event 
+    });
+    if ( this.viewport && stop !== false ) {
         if( !this.panHorizontal ){
             delta.x = 0;
         }
@@ -1207,91 +1234,91 @@ function onCanvasDrag( tracker, position, delta, shift, event ) {
             this.viewport.applyConstraints();
         }
     }
-    this.raiseEvent( 'drag', { 
-        tracker: tracker,
-        position: position,
-        delta: delta,
-        shift: shift,
-        originalEvent: event 
-    });
 }
 
 function onCanvasRelease( tracker, position, insideElementPress, insideElementRelease, event ) {
-    if ( insideElementPress && this.viewport ) {
+    var stop = this.raiseEvent( 'release', { 
-        this.viewport.applyConstraints();
-    }
-    this.raiseEvent( 'release', { 
         tracker: tracker,
         position: position,
         insideElementPress: insideElementPress,
         insideElementRelease: insideElementRelease,
         originalEvent: event 
     });
+    if ( insideElementPress && this.viewport && stop !== false ) {
+        this.viewport.applyConstraints();
+    }
 }
 
 function onCanvasScroll( tracker, position, scroll, shift, event ) {
-    var factor;
+    var factor,
-    if ( this.viewport ) {
+        stop = this.raiseEvent( 'scroll', { 
+            tracker: tracker,
+            position: position,
+            scroll: scroll,
+            shift: shift,
+            originalEvent: event 
+        });
+
+    if ( this.viewport && stop !== false ) {
         factor = Math.pow( this.zoomPerScroll, scroll );
         this.viewport.zoomBy( 
             factor, 
             this.viewport.pointFromPixel( position, true ) 
         );
         this.viewport.applyConstraints();
+        //cancels event
+        event.stopPropagation();
+        event.preventDefault();
+        return false;
     }
-    this.raiseEvent( 'scroll', { 
-        tracker: tracker,
-        position: position,
-        scroll: scroll,
-        shift: shift,
-        originalEvent: event 
-    });
-    //cancels event
-    return false;
 }
 
 function onContainerExit( tracker, position, buttonDownElement, buttonDownAny, event ) {
-    if ( !buttonDownElement ) {
+    var stop = this.raiseEvent( 'exit', { 
-        THIS[ this.hash ].mouseInside = false;
-        if ( !THIS[ this.hash ].animating ) {
-            beginControlsAutoHide( this );
-        }
-    }
-    this.raiseEvent( 'exit', { 
         tracker: tracker,
         position: position,
         buttonDownElement: buttonDownElement,
         buttonDownAny: buttonDownAny,
         originalEvent: event 
     });
-}
+    if ( !buttonDownElement ) {
-
-function onContainerRelease( tracker, position, insideElementPress, insideElementRelease, event ) {
-    if ( !insideElementRelease ) {
         THIS[ this.hash ].mouseInside = false;
-        if ( !THIS[ this.hash ].animating ) {
+        if ( !THIS[ this.hash ].animating && stop !== false ) {
             beginControlsAutoHide( this );
         }
     }
-    this.raiseEvent( 'release', { 
+}
+
+function onContainerRelease( tracker, position, insideElementPress, insideElementRelease, event ) {
+    var stop = this.raiseEvent( 'release', { 
         tracker: tracker,
         position: position,
         insideElementPress: insideElementPress,
         insideElementRelease: insideElementRelease,
         originalEvent: event 
     });
+
+    if ( !insideElementRelease ) {
+        THIS[ this.hash ].mouseInside = false;
+        if ( !THIS[ this.hash ].animating && stop !== false ) {
+            beginControlsAutoHide( this );
+        }
+    }
 }
 
 function onContainerEnter( tracker, position, buttonDownElement, buttonDownAny, event ) {
+    var stop;
     THIS[ this.hash ].mouseInside = true;
-    abortControlsAutoHide( this );
+    stop = this.raiseEvent( 'enter', { 
-    this.raiseEvent( 'enter', { 
         tracker: tracker,
         position: position,
         buttonDownElement: buttonDownElement,
         buttonDownAny: buttonDownAny,
         originalEvent: event 
     });
+    if( stop !== false ){
+        abortControlsAutoHide( this );
+    }
 }
 
 
@@ -1337,16 +1364,20 @@ function updateOnce( viewer ) {
     }
 
     if ( !THIS[ viewer.hash ].animating && animated ) {
-        viewer.raiseEvent( "animationstart" );
+        if( false === viewer.raiseEvent( "animationstart" ) ){
+            return;
+        }
         abortControlsAutoHide( viewer );
     }
 
     if ( animated ) {
+        if( false === viewer.raiseEvent( "animation" ) ){
+            return;
+        }
         viewer.drawer.update();
         if( viewer.navigator ){
             viewer.navigator.update( viewer.viewport );
         }
-        viewer.raiseEvent( "animation" );
     } else if ( THIS[ viewer.hash ].forceRedraw || viewer.drawer.needsUpdate() ) {
         viewer.drawer.update();
         if( viewer.navigator ){
@@ -1356,7 +1387,9 @@ function updateOnce( viewer ) {
     } 
 
     if ( THIS[ viewer.hash ].animating && !animated ) {
-        viewer.raiseEvent( "animationfinish" );
+        if( false === viewer.raiseEvent( "animationfinish" ) ){
+            return;
+        }
 
         if ( !THIS[ viewer.hash ].mouseInside ) {
             beginControlsAutoHide( viewer );

src/viewport.js

@@ -77,6 +77,13 @@ $.Viewport.prototype = {
      * @return {OpenSeadragon.Viewport} Chainable.
      */
     resetContentSize: function( contentSize ){
+        if( this.viewer ){
+            if( false === this.viewer.raiseEvent( 'reset', { contentSize: contentSize } ) ){
+                //cancel event
+                return this;
+            }
+        }
+
         this.contentSize    = contentSize;
         this.contentAspectX = this.contentSize.x / this.contentSize.y;
         this.contentAspectY = this.contentSize.y / this.contentSize.x;
@@ -85,13 +92,6 @@ $.Viewport.prototype = {
 
         this.homeBounds = new $.Rect( 0, 0, 1, this.contentAspectY );
         
-        if( this.viewer ){
-            this.viewer.raiseEvent( 'reset-size', { 
-                contentSize: contentSize,
-                viewer: this.viewer
-            });
-        }
-        
         return this;
     },
 
@@ -133,10 +133,10 @@ $.Viewport.prototype = {
      */
     goHome: function( immediately ) {
         if( this.viewer ){
-            this.viewer.raiseEvent( 'home', { 
+            if( false === this.viewer.raiseEvent( 'home', { immediately: immediately } ) ){
-                immediately: immediately,
+                //cancel event
-                viewer: this.viewer
+                return this;
-            });
+            }
         }
         return this.fitBounds( this.getHomeBounds(), immediately );
     },
@@ -280,6 +280,13 @@ $.Viewport.prototype = {
             dy = 0,
             dx1 = 0, dx2 = 0, dy1 = 0, dy2 = 0;
 
+        if( this.viewer ){
+            if( false === this.viewer.raiseEvent( 'constrain', { immediately: immediately } ) ){
+                //cancel event
+                return this;
+            }
+        }
+
         if ( actualZoom != constrainedZoom ) {
             this.zoomTo( constrainedZoom, this.zoomPoint, immediately );
         }
@@ -332,13 +339,6 @@ $.Viewport.prototype = {
             this.fitBounds( bounds, immediately );
         }
 
-        if( this.viewer ){
-            this.viewer.raiseEvent( 'constrain', { 
-                immediately: immediately,
-                viewer: this.viewer
-            });
-        }
-
         return this;
     },
 
@@ -475,6 +475,18 @@ $.Viewport.prototype = {
      * @return {OpenSeadragon.Viewport} Chainable.
      */
     panTo: function( center, immediately ) {
+        var stop;
+        if( this.viewer ){
+            stop = this.viewer.raiseEvent( 'pan', { 
+                center: center,
+                immediately: immediately
+            });
+            if( stop === false ){
+                //cancel event
+                return this;
+            }
+        }
+
         if ( immediately ) {
             this.centerSpringX.resetTo( center.x );
             this.centerSpringY.resetTo( center.y );
@@ -483,13 +495,6 @@ $.Viewport.prototype = {
             this.centerSpringY.springTo( center.y );
         }
 
-        if( this.viewer ){
-            this.viewer.raiseEvent( 'pan', { 
-                center: center,
-                immediately: immediately,
-                viewer: this.viewer
-            });
-        }
 
         return this;
     },
@@ -507,6 +512,18 @@ $.Viewport.prototype = {
      * @return {OpenSeadragon.Viewport} Chainable.
      */
     zoomTo: function( zoom, refPoint, immediately ) {
+        var stop;
+        if( this.viewer ){
+            stop = this.viewer.raiseEvent( 'zoom', { 
+                zoom: zoom,
+                refPoint: refPoint,
+                immediately: immediately
+            });
+            if( stop === false ){
+                //cancel event;
+                return this;
+            }
+        }
 
         this.zoomPoint = refPoint instanceof $.Point ? 
             refPoint : 
@@ -518,14 +535,6 @@ $.Viewport.prototype = {
             this.zoomSpring.springTo( zoom );
         }
 
-        if( this.viewer ){
-            this.viewer.raiseEvent( 'zoom', { 
-                zoom: zoom,
-                refPoint: refPoint,
-                immediately: immediately,
-                viewer: this.viewer
-            });
-        }
 
         return this;
     },
@@ -537,7 +546,19 @@ $.Viewport.prototype = {
     resize: function( newContainerSize, maintain ) {
         var oldBounds = this.getBounds(),
             newBounds = oldBounds,
-            widthDeltaFactor = newContainerSize.x / this.containerSize.x;
+            widthDeltaFactor = newContainerSize.x / this.containerSize.x,
+            stop;
+
+        if( this.viewer ){
+            stop = this.viewer.raiseEvent( 'resize', { 
+                newContainerSize: newContainerSize,
+                maintain: maintain
+            });
+            if( stop === false ){
+                //cancel event
+                return this;
+            }
+        }
 
         this.containerSize = new $.Point(
             newContainerSize.x, 
@@ -549,14 +570,6 @@ $.Viewport.prototype = {
             newBounds.height = newBounds.width / this.getAspectRatio();
         }
 
-        if( this.viewer ){
-            this.viewer.raiseEvent( 'resize', { 
-                newContainerSize: newContainerSize,
-                maintain: maintain,
-                viewer: this.viewer
-            });
-        }
-
         return this.fitBounds( newBounds, true );
     },