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Comment by bgrins | Hacker News Reader

For an introduction, read the section on limiting DOM manipulation here: http://www.artzstudio.com/2009/04/jquery-performance-rules/#...

Here is the Gecko DOM reference: https://developer.mozilla.org/en/DOM/element (listing common manipulation methods) https://developer.mozilla.org/en/Gecko_DOM_Reference

Basically, if you catch yourself calling DOM functions in a loop (or in a function that gets called in a loop, like the grid_canvas example here), it should be done in memory and then manipulate the DOM outside of the loop.

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Do you know if there's a way to do something similar when displaying images? for a game I need to display a tiled background, and at this time I do it by looping on the x and y axis. That's slow.

Of course I then translate the resulting canvas instead of redrawing everything when I want to scroll but there's still a lot of invalidations involved.

For a tiled repeating background, I would recommend looking into createPattern function https://developer.mozilla.org/en/Canvas_tutorial/Applying_st....

You can use code like this:

    context.fillStyle = context.createPattern(img, 'repeat');
    context.fillRect(0, 0, 100, 100);

Where 'img' is an Image object you loaded from an src, or even a canvas object that you may have used to build a composite background.

If this doesn't work in your situation, I would at least build this image once in a canvas in memory (using document.createElement), and reference it in the 'drawImage' function instead of building it from scratch each time. Though it sounds like you might already be doing this. Do you have a link to your game?

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