[webkit-help] Slow to render images?

Simon Fraser simon.fraser at apple.com
Fri Dec 16 10:43:26 PST 2011

On Dec 15, 2011, at 7:13 PM, Tim Visher wrote:

> Hi Everyone,
> I'm trying to figure out if I'm doing something wrong or if WebKit is
> just inherently slow to render images. I have a javascript slide show
> where I would like to display a serious of fixed position images in
> quick succession. Firefox works very well and uses little to no CPU to
> do this.

Sampling shows that WebKit is spending a lot of time downsampling the images (since you
are shrinking them down), and doing color correction. Does Firefox do color correction on the images?


> WebKit, however, chews up an entire core and displays the images at a
> significantly slower rate than desired.
> It does this in WebKit nightly, Safari, and Chrome.
> I've published a [test page][1]. If I try [significantly simpler][2]
> or [compressed to oblivion][3] images, WebKit seems to perform
> alright.
> [1]: http://random.twonegatives.com.s3-website-us-east-1.amazonaws.com/id-cycle-rendering-demo/
> [2]: http://random.twonegatives.com.s3-website-us-east-1.amazonaws.com/id-cycle-rendering-demo/performant.html
> [3]: http://random.twonegatives.com.s3-website-us-east-1.amazonaws.com/id-cycle-rendering-demo/low-res.html
> I'd like it to perform well so I don't know if someone can suggest
> something I could do to get good performance.
> If anyone reading this is on Stack Overflow, I've also published a
> [question][4] there that hasn't gotten much traction yet, hence this
> post.
> [4]: http://stackoverflow.com/questions/8524241/how-can-i-optimize-images-to-render-efficiently-in-webkit
> Thanks in advance!

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