Developer Journal

written by Tyler Keating

Since there has been so much activity in SproutCore lately in the run up to 1.11.0, I thought it would be best to start a more regular update on the changes occurring in master. While we occasionally highlight a specific new feature in depth through a “Dispatches from the Edge” post, there are actually hundreds of small, yet interesting, changes occurring weekly that aren’t large enough to warrant their own post. It’s my hope to capture these changes in a weekly to bi-weekly developer update. So let’s begin with the last couple of weeks (Note: no changes are final).

Touchy Mice

If you own an Apple Magic Mouse, you may have found some web apps difficult to use. A notable public example of this problem was in the Google Maps app. When you released your finger after dragging the map around, the extra mouse wheel events that were sent as your finger was lifted caused the map to zoom in and out rapidly. Now I believe Google has fixed that problem with their app and we have as well for SproutCore’s SC.SliderView and SC.ScrollView, both of which use mouse wheel events. To prevent the extra mouse wheel events that can occur on click or release from triggering the control, we ignore any mouse wheel events that fire while the mouse is pressed up until 250ms after the mouse up event. Depending on how adept your users are with their mice clicks, the result may be a huge improvement or barely perceptible, but even as small a change as it is to prevent scrolling jiggle on mouse click, it’s just one more brick in the incredible user experience wall that we’re trying to build with SproutCore.


We’ve been working diligently on SC.ScrollView performance (more on that later), but in the process we’ve implemented some other performance improvements.

We fixed a problem with excessive layout updates for certain types of views. If a view used viewDidResize to check for size changes and then make further adjustments to its position, the adjustments to its position would have appeared as further changes to its size. In particular, SC.PickerPane suffered from this, since it re-positions itself whenever its size changes.

Speaking of SC.PickerPane, this one got a performance scrub down. You may not have been aware, but SC.PickerPane now has some special code enabling it to appear within scrollable content and move correctly when the content scrolls. It’s a really nice advanced feature, but there were a couple of issues hampering the performance of it. The first was that the scroll view observers were too greedy observing offsets of the scroll view for changes and repositioning on each change. What this meant was that an SC.PickerPane could reposition itself up to 6 times in a single run loop as the content of the scroll view changed. Instead, the proper pattern for observing multiple properties (or noisy properties) is to filter the input through an invokeX (i.e. so even though 6 calls to the observer function may occur, we only call positionPane once). Additionally, we no longer observe the offsets if the scroll view can’t even scroll and finally, there is a bug fix in there too. When the picker’s anchor gets moved on its own, we ensure that the anchor is in its new position before we re-position.

One of the most important classes within SproutCore has been sped up a bit too. SC.State had two observes helper functions used to be notified when its enteredSubstates and currentSubstates arrays changed. Since these arrays are modified by the owner statechart, the observers needed to be chained enumerable observers. However, this resulted in slower object initialization for each state object and excess observer firing as the entered and current substates change. Instead, we simply notify the target state directly each time that the owning statechart makes a change to its enteredSubstates and currentSubstates. This one has has a couple benchmarks to site:


  • initStatechart in unit tests: ~21ms to ~13ms (~38% faster)
  • initStatechart in large application: ~81ms to ~51ms (~37% faster)

While a reduction of 30ms in a, generally once run, method isn’t much to write home about, we are relentless in shaving every possible millisecond that we can. More notably, we’ve recently made some serious performance improvements to the core SC methods: SC.mixin, SC.supplement as well as to SC.Function.enhance. SC.mixin and SC.supplement iterated the arguments object to insert a boolean flag to pass to a private function that then iterated the arguments again in order to remove the flag argument, which is totally unnecessary. Instead, SC.mixin and SC.supplement iterate the arguments once and pass the new Array to the private function, removing the need for a second iteration.

More importantly though, is that these three areas no longer access the arguments object to copy it, which required the browser to instantiate it and is costly. Instead, we now do a fast copy (similar to this: without instantiating the arguments object. By doing a fast copy of arguments these functions are now optimizable by V8.

Benchmark: SC.mixin & SC.supplement ~ 58% faster

Also,SC.RenderContext‘s setStyle method was updated so that it could be optimized for V8 as well.

SC.ScrollView and SC.MenuScrollView Refactor

This one will actually get its own blog post. For now, I just wanted to mention that these views have seen massive refactoring. The purpose of the changes has been to simplify the logic, which had gotten fairly unruly, but more importantly to grind and grind on the little details so that scrolling and scaling should feel as good and as natural as possible. We’ll post an in-depth on SC.ScrollView in the next couple weeks.

SC.MenuPane Tidy

We fixed SC.MenuPane automatic resizing to fit within the window. The positioning code used in SC.PickerPane failed to apply adjustments to the width or height of the pane, which had been calculated in order to fit long menus within the window. This included improving the menu positioning code to respect the value of windowPadding and fixing a problem where the items array was not observed for content changes if it was set on create.

We removed an unnecessary layout change in createChildViews, which also meant that creating a menu pane as a singleton (i.e. with no run loop) would throw invokeOnce warnings.

WARNING We removed the SC.MenuPane.VERTICAL_OFFSET property. SC.PickerPane already has a provision for offsetting panes from the window’s edges, windowPadding, and that is the property that is being used now.

General fixes and changes

Finally, there are always a large number of little changes. Here are some from the last few weeks.

  • Removed an extra call to SC.RootResponder‘s computeWindowSize each time that a pane is appended. This is unnecessary, since the root responder recomputes its window size property whenever the window actually resizes.
  • Improved the default styling of overlay scroller views. Making them look more like natural overlay scrollers in OS X and making them more visible against dark backgrounds.
  • Improved the view management of SC.ContainerView a bit. If contentView is set as an uninstantiated view class, it will instantiated correctly (you should set nowShowing though normally).
  • Fixed SC.ObserverSet to pass the given context to the observer method. SC.ObserverSet.prototype.add() accepts a third argument, context, but it did not actually pass it along to the observer method.
  • Improved SC.MenuItemView handling of submenus. Previously if the item’s submenu was visible and the mouse exited back onto the menu item view, it tried to re-append the same submenu. Instead, it now checks to see if its submenu is already attached before attempting to enter it again.
  • Fixed a bug in SC.ContainerView‘s override of set so that it may be chainable.
  • Did you know you can cancel animations created with animate in place? This includes transform transitions whose in place value is represented as a 4×4 matrix that must be decomposed to find the current value for translate, scale and rotate in the three planes. We’re still working on rotation around the X and Y axis, but all other transforms can be cancelled. A demo on this will come later.

I apologize that this post is quite long, if it actually included all the work in the scroll and scroller views it would be three times longer, but as you can see, there is a lot going on. I hope to keep these posts much shorter from now on by keeping them more regular.