[webkit-dev] Using RenderLayer for transforms

Maciej Stachowiak mjs at apple.com
Mon Apr 6 12:02:25 PDT 2009

On Apr 6, 2009, at 3:04 AM, Eric Seidel wrote:

> Dave, Simon (and the larger community):
> I've been looking at fixing:
> https://bugs.webkit.org/show_bug.cgi?id=20769
> https://bugs.webkit.org/show_bug.cgi?id=14015
> in SVG.  A large part of the mis-match between SVG renderers and the
> HTML/CSS rendering tree is the use of transforms.
> In SVG, transforms (and clipping) are handled by the renderers
> themselves.  the HTML/CSS rendering tree does not handle transforms,
> and instead only rectilinear layout using parent-offsets.  Things
> which require transforms get a RenderLayer and all the RenderObject
> methods remain transform-ignorant.
> Is this currently the long-term plan for transforms?  Or will HTML
> also be moving to a transform aware rendering tree?

I don't think anyone has immediate plans to make every renderer handle  
arbitrary transforms. What you describe doesn't sound obviously wrong  
to me; transforms on CSS-rendered elements are rare and likely to be  
on only a few elements when used, whereas they are quite common for  
SVG renderers.

> To fix these bugs I will need to sorta "hack" how things like outline
> drawing are done, focus ring invalidation, and repaint rect
> calculation to take transforms into account inside the renderers.

It might be easier to give useful feedback if you give examples of  
alternate ways to fix particular bugs.


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