26 Apr 2012, 11:04am
gwt:

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  • Improving Canvas Performance

    1. Time­out instead of Scheduler

    Sur­pris­ingly, using com.google.gwt.user.client.Timer seems much faster then rely­ing on com.google.gwt.core.client.Scheduler. I did not yet eval­u­ate the dif­fer­ences in detail but the lower CPU work­load speaks for itself.

    2. Ani­ma­tion­Sched­uler

    I am not really sure if this helps a lot, but you will find a lot of online doc­u­men­ta­tion explain­ing that you should use this:
    com.google.gwt.animation.client.AnimationScheduler.get(). requestAnimationFrame(callback, element);. The ele­ment para­me­ter is optional but said to improve per­for­mance as the browser can decide when to ren­der opti­mally.
    So when­ever your timer kicks in, and you are ready to ren­der the results, use the Ani­ma­tion­Sched­uler instead of call­ing your ren­der­ing rou­tines right away. It will only take very few mil­lisec­onds (depend­ing on the users screen frame rate—which is 60 Hz or more usu­ally) for the call­back to return to your code.

    3. Caching

    This parts requires much more effort and depends on your soft­ware archi­tec­ture and require­ments. The basic idea is not to redraw things that did not change. To do so we can draw each item on a hid­den can­vas once and then reuse this ren­der­ing dur­ing every draw­ing cycle.
    As the process is a bit more com­pli­cated, I will ded­i­cate it a sep­a­rate post—comming soon!

    4. Save on effects

    Yes, effects is what the can­vas is all about, but some­thing like a shadow can cost quite some CPU power. So if you run into prob­lems check if some of the effects can be achieved cheaper or even be removed.

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