Tag Archives: AS3

ActionScript 3.0

AIR, AS3, Flash

ActionScript performance tips

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Here are a few simple tricks that may help the performance of your code/graphics intensive Flash movies. This is not an exhaustive list, by any means, rather some of the more effective performance tweaks to try out on your projects. There are the usual sensible coding tricks, like using local variables for oft-used references within functions, or planning your code loops carefully and breaking out of loops whenever feasible – but you should be doing these already. I’ll be adding to this post as and when I feel necessary, but will generally avoid the more granular tricks, such as bytecode optimisation. Some of those methods are too complex to explain in simple terms here and generally have a low effort-to-benefit ratio anyway:

Use scrollRect in conjunction with cacheAsBitmap. The cacheAsBitmap parameter of a movieclip can improve performance dramatically, but will cause problems if the render area of the movieclip gets too large (e.g. larger than 2880 in width or height), regardless of whether it is cropped by the viewable area of the Flash Player. The solution is to use scrollRect to constrain the rendering area to desired limits, in this example, the stage width/height:

import flash.geom.Rectangle;
scrollRect = new Rectangle(0, 0, Stage.width, Stage.height);
cacheAsBitmap = true;

Create bitmap snapshots of complex movieclips. Where you may have a movieclip full of layered graphical effects that isn’t animated, you can save a lot of rendering time by creating a snapshot of the movie. Similar to the cacheAsBitmap parameter, but will improve performance further if your movieclip comprises many lines or alphas. The following function shows a quick and dirty way of duplicating a movieclip as a snapshot of the original:

import flash.geom.*;
function createSnapshot (base:MovieClip, mc:MovieClip):MovieClip {
var bounds = mc.getBounds(base);
var bmpWidth = bounds.xMax-bounds.xMin;
var bmpHeight = bounds.yMax-bounds.yMin;
var bmp1 = new BitmapData(bmpWidth, bmpHeight, true, 0x00000000);
var snapshot = base.createEmptyMovieClip("snapshot"+base.getNextHighestDepth(), base.getNextHighestDepth());
snapshot._x = mc._x;
snapshot._y = mc._y;
var rect = new Rectangle(0, 0, bmpWidth, bmpHeight);
var pos = new Point(0, 0);
bmp1.draw(mc, new Matrix(mc._xscale/100, 0, 0, mc._yscale/100, mc._x-bounds.xMin, mc._y-bounds.yMin));
snapshot.attachBitmap(bmp1, 1, "auto", true);
snapshot._x = bounds.xMin;
snapshot._y = bounds.yMin;
mc.unloadMovie();
return snapshot;
}

Use the opaque window mode trick – sparingly! Setting the wmode=opaque HTML parameter of your Flash object can improve rendering performance, but at a potential cost. Not only does it make the rendering order of movieclips and frames more ‘lazy’, but will effect keyboard interaction adversely in some browsers (especially FireFox). Use with caution.

I’ll be updating and tracking back to this post occasionally, so stay tuned…

AS3

Attaching a Bitmap – AS2 vs AS3

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A common task that has changed drastically in ActionScript 3.0 is loading a library image via its linkageID into a BitmapData object and attaching it to a movieclip. In ActionScript 2.0, this can be done like so:

import flash.display.BitmapData
var bmp:BitmapData = BitmapData.loadBitmap("linkageID");
var img = createEmptyMovieClip("img",0);
img.attachBitmap(bmp,0);

In ActionScript 3.0 movieclips and bitmaps are not attached or created like this – everything is created with the new keyword. Also, a BitmapData object should be dropped into a new Bitmap, which can be added to the stage with the all-important addChild() method.

Since a library bitmap inherits from BitmapData, you now set the class of the bitmap its Linkage Properties in Flash CS3, instantiate it and wrap it in a Bitmap object that you add to the stage:

Attaching a bitmap in AS3

Where ‘Butterfly’ refers to the bitmap library item you’ve given the class definition ‘Butterfly’. The Base class is generated automatically. These five lines of code can be shortened to one, but is less readable:

var img = addChild(new Bitmap(new Butterfly(0,0)));

Note that in Flex Builder, unlike Flash CS3, you would embed an image using the embed meta tag, associating it with a variable, instead of its Linkage Properties dialog:

[Embed(source='image.jpg')] public var Butterfly:Class;

Building SWFs in Flex Builder is a whole different topic – so stay tuned!