1151667 - Scrollable subdocument's area not part of root scrollable layer's dispatch-to-content region on page load

Status: RESOLVED DUPLICATE of bug 1154478

(Core :: Layout, defect)

Description

[Botond Ballo [:botond]]

STR:
  1. Load http://people.mozilla.org/~bballo/iframe.html with APZ enabled
  2. Observe that the iframe is initially not layerized.
     (This may or may not be intentional - see bug 1151663 - but let's
     assume for now it is.)
  3. Position the mouse over the iframe
  4. Scroll down with the mouse wheel

Expected results:
  The iframe scrolls. (The expected mechanism for this is that the
  iframe is contained inside the dispatch-to-content region of the
  root scroll frame, so APZ waits for a set-target-apzc notification
  before scrolling. Content layerizes the iframe, and sets it as
  the target rather than the root scroll frame.)

Actual results:
  The page scrolls initially. (Once the iframe is layerized, it
  then starts scrolling instead.)

(This is also reproducible with a <div> instead of an <iframe> [1]).

[1] http://people.mozilla.org/~bballo/div.html

Comment 1

[Botond Ballo [:botond]]

Still reproductible on a recent nightly. I will investigate.

Comment 2

[Botond Ballo [:botond]]

Looks like initially, the iframe's area is not included in the dispatch-to-content region of the root scrollable layer.

Comment 3

[Botond Ballo [:botond]]

Markus mentioned that the failure of dom/events/test/test_bug574663.html with APZ enabled (which was worked around for the APZ-windows-nightly-enabling) could have the same cause.

Comment 4

[Timothy Nikkel (:tnikkel)]

Are we not hitting this line? http://mxr.mozilla.org/mozilla-central/source/layout/generic/nsGfxScrollFrame.cpp?rev=3c3337ed60a1#3007

Comment 5

[Botond Ballo [:botond]]

The problem is that I was testing with the event-regions pref off.

Bug 1137267 modified nsDisplayListBuilder::IsBuildingLayerEventRegions() to return true if APZ is enabled, even if the event-regions pref is off, but the place in layout code that added inactive scroll frames to the event-regions was checking gfxPrefs::LayoutEventRegionsEnabled() directly rather than checking nsDisplayListBuilder::IsBuildingLayerEventRegions().

Comment 6

[Botond Ballo [:botond]]

Looks like this is fixed by the patch in bug 1154478.