AS3 Flash Efficient Code Techniques, Vectors in Flash 10, Faster JPEG Encoding, Other Optimization Notes
Flash 10 will be ready for mainstream hopefully by the end of this year, or early ’10 when the penetration numbers will be up in or around the 90% range via zeh fernando based on previous trajectories.
With that, Flash 10 has many great new things such as the Vector structure that allows a collection of a certain type, which results in a faster collection because of the known type. So anywhere where Arrays are used, that is a possible candidate for a performance increase within some code because you are asking the virtual machine to do less work on each loop (not having to dynamically find out the type).
ByteArray (Thibault Imbert) has demonstrated that for the JPEG encoding in corelib it is up to 2.5 times faster using Vectors than Arrays. Your mileage may vary heavily but it is almost a guaranteed speed boost due to less work. This obviously has great possibilities for speeding up code that uses lots of arrays.
Due to the performance boost the Vector does have some constraints in the typical give and take of coder flexibility with compiler and virtual machine overhead. Vectors are more explicit and strongly typed which is why they are fast, but this is also limiting.
In addition to the data type restriction, the Vector class has other restrictions that distinguish it from the Array class:
- A Vector is a dense array. Unlike an Array, which may have values in indices 0 and 7 even if there are no values in positions 1 through 6, a Vector must have a value (or
null) in each index.
- A Vector can optionally be fixed-length, meaning the number of elements it contains can’t change.
- Access to a Vector’s elements is bounds-checked. You can never read a value from an index greater than the final element (
length - 1). You can never set a value with an index more than one beyond the current final index (in other words, you can only set a value at an existing index or at index
[ Vector docs ]
ByteArray not only used Vectors heavily but did other optimizations that are always good to do, even though optimization is evil when you are working with precious client side resources ensuring an optimized base starting point can be a good thing.
So what did I do ?
- I used bitwise operators as much as possible.
- I replaced all Arrays with fixed length Vectors.
- I used pre-incrementation rather than post-incrementation (thanks Joa for this one ;)).
- I casted to int all my Vector indices access.
- Other minor stuff you always do to optimize your code
Other sources as well for even more optimization or shall I say efficient AS3:
- Polygonal Labs Using Object Pools
- Joa Ebert Tweening and Object Pools
- Joa Ebert Optmization Wiki
- Sean Moore Efficient AS3 roundup (great list of resources for more at the bottom)
- Lost in Actionscript Efficient AS3 Tips
- Big SpaceShip Mouse Leave Tip (flash can hog resources so when it isn’t in focus then let is stop tasking the processor)
- Grant Skinner Idle CPU in AIR FPS Tip (set fps to a lower amount when it is out of focus)