Archive for the ‘AS3’ Category

Switch-case for object’s class type

Friday, August 31st, 2012

Quick tip; instead of using a bunch of “if (x is y) else if (x is z) else” conditionals, you can simply get the class of any object using the “constructor” property. It’s not exposed trough strict typing though, so you have to typecast your instance to Object to access it.

This allows you to have a switch-case for an object’s class:

function addShape(shape:Shape):void {
	switch (Object(shape).constructor) {
		case Circle:
			trace("It's a circle");
		case Square:
			trace("It's a square");
			trace("Unknown shape");

Mouse scroll wheel in flash not working in Chrome

Tuesday, August 14th, 2012

Chrome’s latest update to version 21 introduced a new type of flash player using the PPAPI (pepper) plugin architecture.
I noticed that this version of flash started breaking mouse scroll wheel support for some flash content.

Which flash files break and which don’t depend on one thing; if you are using JavaScript to prevent the default behavior of the mouse scroll wheel or not.

The reason for preventing default mouse scroll wheel behavior is for when you don’t want the page to scroll when you scroll over the flash content.
To prevent that, developers write JavaScript code (or use libraries like SwfWheel.js) that add an event listener for the “mousewheel” or “DOMMouseScroll” event, and in the handler call “evt.preventDefault()” and/or “evt.returnValue = false” to cancel the scroll.

Therein lies the problem, the old NPAPI Flash Player would receive the mouse scroll event even if we prevented the default behavior. Maybe even incorrectly so, since the event was cancelled.
The new PPAPI Flash Player will not receive the event if the default is prevented.

If one were to remove the preventDefault() function, the Flash file would start working correctly again, but the whole page would again start scrolling, which is out of the question.

You will have to not only prevent the default scroll behavior, but also call an external interface function in your flash file to let it know when the user scrolls the mouse wheel.
In my case I was using SwfWheel and only needed a small modification to the library file: in the SWFWheel.getState() function add this code before the “if (br.mac)” line:

// The new pepper plugin requires chrome to always be hacked.
if (

VerifyError: Error #1024: Stack underflow occurred.

Tuesday, July 31st, 2012

I just completed hunting down a Stack underflow error. It was a little tedious since the error is not thrown when I compiled for debug player, only release.
The source of it? A trace statement in a try block. For some reason the compiler doesn’t like that at all.

The solution seemed to be to remove all traces from try-catch blocks, which worked, but I wasn’t satisfied.

After binary searching trough the svn commits, I found what triggered the above error, an empty for-each loop.
Removing that loop made all traces work again normally inside try-catch blocks, which is what I prefer.

for each (var fruit:String in fruits) {
   // Empty loop, a BIG NO NO!

So to prevent your swf from corrupting, do not have empty for-each loops in your project! Remove them completely or fill them with some code.

Throwing an error in a constructor before the super() statement

Friday, April 13th, 2012

I would have thought you could throw an error whenever you pleased like it, however the Flex compiler has some other ideas.

If you have a throw statement before the super() in the constructor, Flex will complain with the following error code:
1201: A super statement cannot occur after a this, super, return, or throw statement.

There is a workaround though, just wrap the throw statement in an anonymous function:

(function():void {
	throw new Error("Yay for workarounds!");

Error #3692: All buffers need to be cleared every frame before drawing

Friday, November 18th, 2011

So I have this Starling project and wanted to take a screenshot of the Stage3D currently in use.
I was trying to use the Context3D.drawToBitmapData() function and kept getting this error:
“Error #3692: All buffers need to be cleared every frame before drawing.”

Googling around yielded no results, so after figuring out the problem I’m posting the solution here for anyone else having this problem.

The solution is short: you have to call drawToBitmapData() BEFORE the Context3D.present() call.

In my case with Starling I had to add the functionality in the Starling.render() function, between the call to mStage.render() and the call to mContext.present().

Mxmlc ANT compiler error: “Error: Java heap space”

Thursday, September 29th, 2011

A simple error that causes a lot of headache that has a simple solution that is hard to find on the internet.
Don’t you just love these problems?

If you are calling mxmlc via ANT you’ve probably seen this error and had to resort to solutions like setting the ANT_OPTS or Java arguments for the SDK on every single computer that uses that build script.

The solution is actually much simpler than that, mxmlc allows you to set this in the ANT target itself. Just add the parameters fork=”true” to make it run on it’s own Java thread, and then set maxmemory to something like “1024m”.


It would have been nice if adobe had this in the documentation, but no such luck.

AS3 Polygon Clipper

Monday, May 23rd, 2011

I was looking for an open source polygon clipper library for AS3 to use on a commercial project.
I found a few ports of the General Polygon Clipper library (GPC) but it is only free for non-commercial projects.
After more searching around I found this excellent library called Clipper by Angus Johnson. It did not have an AS3 port so I made one using Alchemy to wrap the c++ code.

The SWC and source code can be found on github:

It is completely free and open source for both personal and commercial projects. Clipper uses the Boost Software License.

Supported clipping operations: difference, intersection, union and XOR.

Here’s an example of how to use the AS3 port after importing the Clipper.swc file:

import com.flassari.geom.Clipper;
import com.flassari.geom.ClipType;

var subjectPolygon:Array = [new Point(0, 0), new Point(200, 0), new Point(100, 200)];

var clipPolygon:Array = [new Point(0, 100), new Point(200, 100), new Point(300, 200)];

var resultPolygons:Array = Clipper.clipPolygon(subjectPolygon, clipPolygon, ClipType.DIFFERENCE);

There is now an AS3 port available at

Prefixing private variables with an underscore in AS3

Tuesday, April 26th, 2011

A coworker and I had a discussion about using underscores for private variables in AS3.
I’ve always added an underscore before my private variables, like so:

private var _myVariable:int;

While he wanted to only use underscores for when you have a variable which has a getter/setter:

private var _myGetAndOrSetVariable:int;
private var myPrivateVariable:int;

public function get myGetAndOrSetVariable():int {
	return _myGetAndOrSetVariable;

This was a little alien to me and I didn’t get the point of it. Why should you only sometimes use an underscore? He answered that then you know that private variable has a getter/setter if it has an underscore.

Well, that’s not a bad reason. I googled around and it sounds like Adobe actually enforces this kind of rule in their Coding Conventions document; “Give the storage variable for the getter/setter foo the name _foo.”.
They don’t say anything about if the other variables shouldn’t have underscores though, so I dived into the source code of the Flex SDK to see what they were using.
Turns out, both! In some classes every single private variable had an underscore, and in other ones only variables with a public getter/setter had one.
In this poll, majority of AS3 developers always use underscores.

I thought long and hard, and I came up with these reasons for why one should always use underscores for private variables:

  • It can be confusing “sometimes and sometimes not” putting an underscore.
  • You can see immediately if the variable is accessible to another class when you always prefix private variables with underscores.
  • Most of the in-house code and frameworks always use underscores (consistency).
  • Pressing ctrl+space for IDE code completion shows you all the local private variables if you type an underscore first, if you don’t you get every single variable in the class with every class in the project together in one gigantic list.
  • Most other coders and their frameworks online use it.
  • If you are going to create a getter/setter for the variable, you have to rename it first to include the underscore.
    • Also, if you rename it without refactoring, all references in the class will now pull from the getter (possible calling extra code) when maybe they were only supposed to get the raw data.
  • If the other method is used I will know much less about the variable just from looking at it, possible making debugging harder. It could be a local variable, a class function, a function parameter, a private variable without a getter/setter, a getter/setter function or a public variable.

Personally, I don’t really care when I’m writing code in a class if a variable has a getter/setter. That’s encapsulation, and I think mostly of it when working in/thinking of other classes that interact with the current one. I much more care knowing if I’m working with a variable or calling a getter function (it could be a public variable too, but still less complicated).
I also prefer to write “_id = id” instead of “ = id”.

Also, adding an underscore just to avoid a name conflict doesn’t sound proper to me. It sounds like you had to make a workaround to make the code do what you want (read: a shit mix).

So far these are enough reasons for me to stick with prefixing my private variables with underscores. I have an open mind though, a comment can easily change my mind if it has the right arguments.

What is your method, and why? Please do share =)

Populating a Vector in the constructor

Wednesday, January 19th, 2011

There is a small difference between populating a Vector while instancing it and an Array.
While an Array is instanced this way:

var names:Array = ["Bob", "Larry", "Sarah"];

a Vector can be instanced like this:

// In the constructor
var names:Vector.<String> = new <String>["Bob", "Larry", "Sarah"];
// Converting from a regular Array using the Vector global (about three times slower)
var names:Vector.<String> = Vector.<String>(["Bob", "Larry", "Sarah"]);

Preloader without a loader-swf in AS3

Wednesday, November 17th, 2010

Here’s one method of loading your AS3 movie, using a preloader class that loads before all other classes.

The flex compiler can actually split up the code for you so one class loads before all others. Even though we’re using the flex compiler to do this we do not have to have a Flex project, it can be a Flash project or a pure actionscript project. If we’re using a Flash project we do have to set the flex compiler path though.

Anyways, the way it works is that in your main class you add the Frame metadata, like this:

package com.flassari {
// Preloader meta tag
// Start of our own application code
[SWF(backgroundColor="#FFFFFF", frameRate="24", width="800", height="600", pageTitle="My preloaded project")]
public class Main extends Sprite

The preloader has to extend movieClip, because behind the scenes it is using frames for its magic.
In your preloader class, when it is done loading (by checking if it is at the last frame), your have to instantiate the main class with no strict typing. If you were to use strict typing, the whole application would have to load before the preloader can be shown so that would defeat the purpose of a preloader:

private function onEnterFrame(e:Event):void {
	if (currentFrame == totalFrames) { // If we're at the frame where Main is ready
		// Stop and clean up
		removeEventListener(Event.ENTER_FRAME, onEnterFrame);
		// Create the main application and add it to the display list
		var mainClass:Class = getDefinitionByName("com.flassari.Main") as Class;
		addChild(new mainClass() as DisplayObject);

Just remember, everything that the preloader references will be loaded before the preloader can be shown, so keep it to a minimum.
Also, because the main class is created before it is put on the stage, be sure not to reference the stage in the constructor.