[webkit-dev] Avoid extra page layout on resize

[Artem Ananiev]

Hi,

I have a question about the way webkit layouts page contents, and what 
is the right way to implement ScrollView class. In my current 
implementation (Java platform) I see the following:

1. Suppose user resizes the window, so the top-most frame/scroll view 
has the size 800x600.

2. Scroll view updates its values (frame geometry, visible rect, etc.) 
and calls layout() to relayout the page.

3. If the page doesn't fit into 800x600, say, it is 1200 in height, then 
WebKit calls scroll view's resizeContents() method with 800x1200.

4. As the requested contents height is greater than scroll view height, 
vertical scrollbar appears, and the page needs relayout again.

5. In the second layout, WebKit calls resizeContens() with the smaller 
width (say, 780, if scrollbar is 20 pixels wide) and some height (say, 
1230).

This two-steps layout process looks strange to me. It also leads to 
extra repaints, and the performance is not as good as desired. The 
question is: (at the step 3) why resizeContents() is called with 800 as 
a value of width, while it is clear that contents doesn't fit to the 
page and vertical scrollbar is required? What methods must be 
implemented by platform, so WebKit may take vertical scrollbar into 
consideration before it actually appear?

Thanks,

Artem