I've done a bit of job to get this done. Right now readback is still used, but we have a `LayerId` -> `CanvasRenderer` map on the paint task, that we can use to get rid of that.
I'd want review, to see if this is a good approach (I know it's not the initial `CanvasId` -> renderer approach, but it's pretty similar, since a canvas involves a `PaintLayer`).
I had to do a bit of refactoring to avoid cyclic dependencies between canvas and gfx. I'd want you to review them too.
It's mergeable and doesn't break any tests :P
Some of my main concerns:
* Does the canvas render really need to be behind an `Arc<Mutex<T>>`?
* I can't clone a `NativeSurface` right now (that's why the `SendNativeSurface()` msg is unimplemented in the WebGL task). It should be easy to add that to rust-layers, supposing the caller is responsible to mark it as non-leaking, any reason to not do it?
cc @jdm @pcwalton
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Added support for the tabindex field, also added its correct defaults (-2 TODOs for things not supported in Servo yet). Also added tabindex logic into Element::is_focusable_area.
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image fragments.
This also changes the way the placeholder is handled in the image cache
task to decode it up front instead of each time an image fails to load,
both because it was more convenient to implement that way and because
it saves CPU cycles to do so.
This matches the behavior of Gecko and WebKit. It improves the look of
our cached copy of Wikipedia.
This improves Servo's performance on large pages.
Please double-check the logic when it comes to nested layers—I'm sure I've messed up some of the geometry calculations :)
r? @glennw
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The [current implementation](http://mxr.mozilla.org/servo/source/components/script/dom/element.rs#666) is wrong as it always tries to cast the furthest ancestor into an element.
When the method is invoked on an element that is in the document tree, this will be the `Document` node, which is not an element. The ```last().map(ElementCast::to_temporary)``` returns Some(None) hence the method will return ```None```, while the correct behaviour is to return the ```html``` node.
This PR interprets the line ```"furthest ancestor element node of whatever node is being discussed"``` in the spec to mean ```"find the furthest ancestor that is an element node"```.
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This property determines the background positioning area, that is the position of
the origin of an image specified using the 'background-image' CSS property.
'background-origin' is ignored when background-attachment is fixed.
Spec: http://dev.w3.org/csswg/css-backgrounds-3/#background-originFixes#6045.
