1192633 - Overlay scrollbars on OS X no longer fade out with an animation, they just disappear

Status: RESOLVED DUPLICATE of bug 1192192

(Core :: CSS Parsing and Computation, defect)

Description

[Markus Stange [:mstange]]

STR:
 1. Be on Mac OS 10.7+ and set your system scrollbars pref to "show when scrolling".
 2. On a scrollable page in Firefox, scroll slightly and then stop.

Expected results:
The scrollbars should fade out smoothly.

Actual results:
They just disappear after a short delay without any animation.


The fade-out animation is implemented in ScrollbarActivity.cpp with a refresh driver observer that animates the opacity property by setting inline styles on the respective <scrollbar> element (which is native anonymous content of the scroll frame), like this:

static void
SetOpacityOnElement(nsIContent* aContent, double aOpacity)
{
  nsCOMPtr<nsIDOMElementCSSInlineStyle> inlineStyleContent =
    do_QueryInterface(aContent);
  if (inlineStyleContent) {
    nsCOMPtr<nsIDOMCSSStyleDeclaration> decl;
    inlineStyleContent->GetStyle(getter_AddRefs(decl));
    if (decl) {
      nsAutoString str;
      str.AppendFloat(aOpacity);
      decl->SetProperty(NS_LITERAL_STRING("opacity"), str, EmptyString());
    }
  }
}

mozregression gave me this range and unfortunately couldn't find any inbound builds for it:
https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=f3b757156f69&tochange=2fad09a0540d

Bug 1180118 is in this range, so I'm assuming it is to blame. I haven't confirmed this.

Comment 1

[Markus Stange [:mstange]]

[Tracking Requested - why for this release]: very visible regression

Comment 2

[Cameron McCormack (:heycam)]

Pretty plausible bug 1180118 is responsible.  It's probably the same as bug 1192302, not traversing into anonymous content (I think?) properly.

Comment 3

[Cameron McCormack (:heycam)]

We probably need to traverse the frame tree to find the elements that we convert eRestyle_SomeDescendants into eRestyle_Self for, rather than traversing the DOM itself.  This would need to look at the undisplayed content, like ElementRestyler::RestyleChildren does, but would also need to do a DOM traversal to the descendants of the display:none child.

Comment 4

[Cameron McCormack (:heycam)]

I bisected further and found that it's actually bug 1186236.

Jerry, can you look into this?

Comment 5

[Jerry Shih[:jerry] (UTC+8) (inactive)]

I think bug 1192192 could fix the problem.

Hey Cameron,
Does bug 1192192 fix this?

Comment 6

[Cameron McCormack (:heycam)]

That does fix it, thanks!

Comment 7

[jen strickland :jenstrickland]

Since this is a duplicate of bug 1192192, and that bug fixes the issue, I'll clear the tracking requested flag.