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Tuesday, September 21, 2010

CSS3 Star Wars Tweet Scroller

I've been playing around with some new CSS3 3-D transforms and whipped up this Star Wars scroller for Tweets:


Caveat: This currently only works on Safari.  It may work on a bleeding edge Chrome dev build but I haven't tried that.

There are some other examples of this type of scrolling effect out there but I wanted to make one for tweets.  I also noticed that there are some odd effects if you naively keep appending content to a div that's been rotated in 3-D.  As it reaches a certain height, webkit apparently starts downsampling (I guess to save memory in the rendering pipeline?  A limitation of hardware?  Who knows) and you get this pixelated effect:

This isn't a downsampled down screen shot.  It actually looks like this if you let the rotated div get too large.
As you can see, it becomes unreadable after a while.  It also starts eating up an increasing amount of CPU: it got to 100% (out of 400%) on my quad core iMac after a few minutes.  Not good.

So instead of putting all of the tweets into the same rotated div, I rotate each tweet element individually and that seems to fix the problem.  Also, I start deleting tweets at the top (where you can no longer see them anyways) after a while, just to keep the dom size down.  They are now readable and the CPU is happy.

Other stuff:

Instead of using CSS3 animations, I opted for javascript because I was loading the tweets with JS already and I'd have to manipulate the animations with JS anyways.

Also, the background is generated dynamically using the Canvas element.  I wanted a more realistic looking star field so I did some research on the distribution of star sizes and colors to see if I could perhaps simulate it with a Pareto distribution.  Turns out the distribution of star colors and brightness is some other weird distribution so I just made it more or less random, with smaller stars slightly more frequent than larger stars.

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