[webkit-dev] Making overflow clipping cheaper

David Hyatt hyatt at apple.com
Wed Jan 4 13:33:52 PST 2012

On Jan 4, 2012, at 2:36 PM, Julien Chaffraix wrote:

>>  namely RenderLayer is too generic for most cases and ends
> up hurting performance.

In what way?

Overflow clips create layers, but they do not paint or hit test at the layer level unless they are self-painting layers. They only become self-painting layers if some other property is present that causes this to happen, e.g., absolute positioning.

Perhaps you could point me to the specific performance problems that you're seeing that are caused by overflow and layers, since we already should be avoiding the self-painting layer code paths for overflow that doesn't need a layer for some other reason.

Note I have no real objection RenderLayers using mix-ins or composition to bring in scrolling functionality. That seems sensible if that's all you're planning. I'd just like to understand the performance concerns more, since it's not clear to me what your specific performance issues are.

(hyatt at apple.com)

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