I’ve had a few people ask for more information on the ActionScript 3 workshop I’m running in Toronto at the end of September, and I thought it would be good to clarify the course goals.

This is not a beginner workshop. It is firmly targeted at developers who have a working knowledge of ActionScript 2, and want a fast way to get running with AS3. As such, I will not be covering any basic programming concepts, but instead will focus on differences between AS2 and AS3, and the new features of the language. It will be filled with tips, tricks, best-practices, and gotchas I’ve picked up while applying AS3 to both experimental and commercial projects.

It is lecture format, but with room for some open discussion and Q&A. Attendees will be given comprehensive course notes, and source code for all in-course examples.

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We recently encountered a problem where bitmap images that we created dynamically were not being properly smoothed when rotated and scaled. We couldn’t see any obvious reason for it – we were setting the container bitmap to smooth, tried every quality setting, but it still looked terrible.

The answer turned out to be super simple, if not immediately obvious. The Bitmap object in ActionScript 3 reverts its .smoothing property to false whenever you change it’s .bitmapData property. Because we were setting up our Bitmap objects in advance, then assigning BitmapData objects to them when they were created, it simply appeared as though smoothing just didn’t work in our project.

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I found a very problematic and reproducible bug with ActionScript 3 and simple display object transformations (width, height, rotation), and thought I should document it to save other developers some debugging time.

Put a 200x200px square clip on stage named foo. Add the following code.

foo.height = 100;
foo.rotation = 90;
trace(foo.height);

As expected, this traces 200. It scales the clip vertically, then rotates it, so that it is now 100px wide and 200px high on stage. Now, change the code, and run it again.

foo.rotation = 90;
foo.height = 100;
trace(foo.height);

Unexpectedly, this also returns 200. It should rotate the clip and then apply the vertical scale resulting in a shape that is 100px high and 200px wide on stage. The visual result is identical to the above, when it shouldn’t be.

foo.rotation = 90;
foo.height = 100;
foo.height = 100;
trace(foo.height);

Even stranger, this does trace 100. Unfortunately, the object has been scaled both vertically and horizontally, and is now 100x100px, when it should be 200px wide and 100px high. Seems like the first height assignment gets applied before the rotation, and the second gets applied after the rotation.

Click here to see a (very) simple demo of this behaviour. The left and right blocks should be the same dimensions.

Freaky. I would hazard a guess that this is related to AS3’s weird hybrid of display object properties and transform matrixes.

One workaround would be to work with scaleX and scaleY instead, which are always applied to the original dimensions, and do not account for rotation.