[webkit-dev] Making overflow clipping cheaper

[Julien Chaffraix]

> Wouldn't it be better to implement better searching and paint-segmentation in
> RenderLayers then? It could also provide the same speed up for many other big
> cases.

That would be worth investigating more for sure (do you mind filing a
bug about it?). The paint search and segmentation algorithm is very
close between RenderLayer and most RenderObjects - tables being an
exception here as their structure enables better searching algorithms
- which means that it would benefit everyone. I haven't spend enough
time looking at generic scalability issues to say if there won't be
others more important bottlenecks.

I still see some upsides in attacking the reduced use case of overflow
clips independently of what you are proposing:
* RenderLayer has become a class handling far too many tasks so moving
some functionality out of it is good by itself.
* RenderObject has a better knowledge of its own structure, something
as generic as RenderLayer would not need to be aware of.

Thanks,
Julien