On 10/6/14 5:17 PM, Martin Robinson wrote:
There isn't a lot in the way to extend this model to
overflow:scroll. The layout code would simply need to make a layer for
the content inside the scrolling flow and a layer for the scrolling
root. The two main dependencies for this would be:
a. Adding a way for layers to trigger the masks_to_bounds flag.
b. Adding support for building layer trees, since all layers are now
added as direct children of their frame root layer.
1. If the content was larger than the scrolling root, it would not be
able to move around inside the scrolling root. Imagine a browser window
that is larger than the content that it contains.
2. The main frame's scroll root size is defined by the window size.
Yes, this is essentially the design I had in mind to handle
`overflow:scroll`. We should try to unify the `position:fixed` code path
and the `overflow:scroll` code paths as much as possible, since they do
similar things. It would also be good to keep CSS 3D transforms, CSS
animations/transitions, and will-change in mind as well for the future.
(Basically, all this stuff falls under the category of "CSS-influenced
attributes assigned to layers that the compositor treats specially".)
Patrick
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