Implement new convention when to call event.preventDefault() after mouse-events:

- If any of the handlers were called, except for mousemove events which need to call `event.preventDefault()` explicitly, or `return false;`.
- If this is a mousedown event, and the view or tools respond to mouseup.

src/core/Emitter.js

@@ -85,20 +85,14 @@ var Emitter = {
         // won't throw us off track here:
         handlers = handlers.slice();
         for (var i = 0, l = handlers.length; i < l; i++) {
-            var res = handlers[i].apply(this, args);
+            if (handlers[i].apply(this, args) === false) {
-            // Look at the handler's return value to decide how to propagate:
+                // If the handler returns false, prevent the default behavior
-            if (res === false) {
+                // and stop propagation of the event by calling stop()
-                // If it returns false, prevent the default behavior and stop
-                // propagation of the event by calling stop()
                 if (event && event.stop)
                     event.stop();
                 // Stop propagation right now!
                 break;
-            } else if (res === true) {
+           }
-                // If it return true, remember that one handler wants to enforce
-                // the browser's default behavior. This is handled later.
-                event._enforced = true;
-            }
         }
         return true;
     },

src/event/Event.js

@@ -26,8 +26,6 @@ var Event = Base.extend(/** @lends Event# */{
 
     prevented: false,
     stopped: false,
-    // Internal flag indicating whether the default shall be enforced.
-    _enforced: false,
 
     /**
      * Cancels the event if it is cancelable, without stopping further

src/tool/Tool.js

@@ -282,9 +282,7 @@ var Tool = PaperScopeItem.extend(/** @lends Tool# */{
     /**
      * Private method to handle tool-events.
      *
-     * @return {@true if the default event should be prevented}. This is if at
+     * @return {@true if at least one event handler was called}.
-     *     least one event handler was called and none of the called handlers
-     *     wants to enforce the default.
      */
     _handleEvent: function(type, event, point, mouse) {
         // Update global reference to this scope.
@@ -301,8 +299,7 @@ var Tool = PaperScopeItem.extend(/** @lends Tool# */{
             // case it is shorter than maxDistance, as this would produce weird
             // results. matchMaxDistance controls this.
             matchMaxDistance = false,
-            called = false, // Has at least one handler been called?
+            called = false,
-            enforced = false, // Does a handler want to enforce the default?
             tool = this;
 
         function update(start, minDistance, maxDistance) {
@@ -348,14 +345,9 @@ var Tool = PaperScopeItem.extend(/** @lends Tool# */{
         }
 
         function emit() {
-            if (tool.responds(type)) {
+            called = tool.responds(type)
-                var toolEvent = new ToolEvent(tool, type, event);
+                    && tool.emit(type, new ToolEvent(tool, type, event))
-                if (tool.emit(type, toolEvent)) {
+                    || called;
-                    called = true;
-                    if (toolEvent._enforced)
-                        enforced = true;
-                }
-            }
         }
 
         if (mouse.down) {
@@ -383,7 +375,7 @@ var Tool = PaperScopeItem.extend(/** @lends Tool# */{
                 }
             }
         }
-        return called && !enforced;
+        return called;
     }
     /**
      * {@grouptitle Event Handling}

src/view/View.js

@@ -838,8 +838,7 @@ new function() { // Injection scope for mouse events on the browser
      * with support for bubbling (event-propagation).
      */
 
-    var called = false, // Has at least one handler been called?
+    var called = false,
-        enforced = false, // Does a handler want to enforce the default?
         // Event fallbacks for "virutal" events, e.g. if an item doesn't respond
         // to doubleclick, fall back to click:
         fallbacks = {
@@ -847,8 +846,7 @@ new function() { // Injection scope for mouse events on the browser
             mousedrag: 'mousemove'
         };
 
-    // Returns true if event was stopped, false otherwise, whether handler was
+    // Returns true if event was stopped, false otherwise.
-    // called or not!
     function emitEvent(obj, type, event, point, prevPoint, stopItem) {
         var target = obj,
             mouseEvent;
@@ -865,8 +863,6 @@ new function() { // Injection scope for mouse events on the browser
                 }
                 if (obj.emit(type, mouseEvent)) {
                     called = true;
-                    if (mouseEvent._enforced)
-                        enforced = true;
                     // Bail out if propagation is stopped
                     if (mouseEvent.stopped)
                         return true;
@@ -887,13 +883,11 @@ new function() { // Injection scope for mouse events on the browser
         return false;
     }
 
-    // Returns true if event was stopped, false otherwise, whether handler was
+    // Returns true if event was stopped, false otherwise.
-    // called or not!
     function emitEvents(view, item, type, event, point, prevPoint) {
-        // Set enforced and called to false, so it will reflect if the following
+        // Set called to false, so it will reflect if the following calls to
-        // calls to emitEvent() have called a handler, and if  at least one of
+        // emitEvent() have called a handler.
-        // the handlers wants to enforce default.
+        called = false;
-        called = enforced = false;
         // First handle the drag-item and its parents, through bubbling.
         return (dragItem && emitEvent(dragItem, type, event, point,
                     prevPoint)
@@ -958,7 +952,7 @@ new function() { // Injection scope for mouse events on the browser
             var handleItems = this._itemEvents[type],
                 project = paper.project,
                 tool = this._scope.tool;
-            // If it's a native mousemove event but the mouse is clicke, convert
+            // If it's a native mousemove event but the mouse is down, convert
             // it to a mousedrag.
             // NOTE: emitEvent(), as well as Tool#_handleEvent() fall back to
             // mousemove if the objects don't respond to mousedrag.
@@ -1054,8 +1048,17 @@ new function() { // Injection scope for mouse events on the browser
             // to only be fired if we're inside the view or if we just left it.
             // Prevent default if at least one handler was called, and none of
             // them enforces default, to prevent scrolling on touch devices.
-            if (handle && tool && tool._handleEvent(type, event, point, mouse)
+            if (handle && tool)
-                    || called && !enforced)
+                called = tool._handleEvent(type, event, point, mouse) || called;
+            // Call preventDefault()`, but only according to this convention:
+            // - If any of the handlers were called, except for mousemove events
+            //   which need to call `event.preventDefault()` explicitly, or
+            //   `return false;`.
+            // - If this is a mousedown event, and the view or tools respond to
+            //   mouseup.
+            var up = 'mouseup';
+            if (called && !mouse.move || mouse.down && (this._itemEvents[up]
+                    || this.responds(up) || tool.responds(up)))
                 event.preventDefault();
             // In the end we always call update(), which only updates the view
             // if anything has changed in the above calls.