[Webkit-unassigned] [Bug 93755] ShadowRoot insertion point change aborts css transition

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=93755


Takashi Sakamoto <tasak at google.com> changed:

           What    |Removed                     |Added
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                 CC|                            |tasak at google.com




--- Comment #1 from Takashi Sakamoto <tasak at google.com>  2012-08-13 03:23:42 PST ---
(In reply to comment #0)
> Created an attachment (id=157837)
 --> (https://bugs.webkit.org/attachment.cgi?id=157837&action=review) [details]
> Reduction showing unexpected result and expected result when altering dom not using an insertion point.
> 
> If an insertion point select attribute in a shadowRoot is changed synchronously with a css change that should provoke a transition, the transition does not occur.
> 
> It is possible to address this problem by using webkitRequestAnimationFrame to provoke the transition.
> 
> If this is the intended behavior it should be noted that it is unlike other similar changes to dom (e.g. appending a node to the document and provoking a transition on it can be done synchronously.)

I investigated the bug and I'm now thinking of how to fix this issue. I think, this is caused by reattach in Element::recalcStyle.

(1) Changing insertion point's select causes the shadow host's reattach. (c.f. ElementShadow::invalidateDistribution().  if (needsReattach && host->attached()) { host->detach(); ...)

(2) Element::recalcStyle for the shadow host invokes reattach() because the host was detached.

(3) During the reattach, the shadow host's renderer is re-created, and RenderObject::setAnimatableStyle is invoked. So animation()->updateAnimations() is also invoked. (animation is an instance of class AnimationController).

(4) AnimationController::updateAnimations doesn't create ImplicitAnimation because currentStyle == null. (transitions() requires currentStyle != 0, but as renderer was detached, currentStyle was set to be null. i.e. the condition: (renderer->parent() || newStyle->animations() || (oldStyle && oldStyle->animations())) is false.

(5) All styles are resolved, but no transitions are started.

So, 
   r.querySelector("content").setAttribute("select", "*:last-child");
    // expected to provoke a css transition but does not.
+  document.body.offsetLeft;
    ts.classList.add("fade");

adding "document.body.offsetLeft;" before ts.classList.add("fade"), css transition for distributed nodes will work.

Best regards,
Takashi Sakamoto

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