176800 - Avoid sending coords for mouse wheel events when no move occurs

Status: NEW

(Core :: XUL, defect)

Description

[David Hyatt]

An optimization.  The point on a mouse scroll event becomes irrelevant if you're
in the middle of wheeling (it's only relevant for the first of several wheels).

Speeds up mouse wheeling pretty substantially for me on some pages.

Comment 1

[David Hyatt]

Attachment: Patch.

Comment 2

[Boris Zbarsky [:bzbarsky]]

Does this change the way these events are viewed in the DOM too?  Or do we not
usefully expose them in the DOM yet?

Comment 3

[David Hyatt]

Attachment: Better patch. Make it a global var.

Comment 4

[Brian Ryner (not reading)]

Comment on attachment 104204 [details] [diff] [review]
Better patch. Make it a global var.

Lose the unneeded whitespace changes and r=bryner.

Comment 5

[Boris Zbarsky [:bzbarsky]]

Comment on attachment 104204 [details] [diff] [review]
Better patch. Make it a global var.

sr=bzbarsky if bryner's happy.

Comment 6

[Stephen Walker]

hyatt, can you check this patch in?

Comment 7

[Brian Ryner (not reading)]

taking.

Comment 8

[Brian Ryner (not reading)]

Bringing jkeiser in since he's been doing heavy lifting with mouse events
lately.  The basic idea is that the only reason an event coordinate would be
important for a mousewheel event is to clear the hover state on the content that
the mouse pointer was previously over.  Since we don't set :hover on any new
content until the mouse is moved, there's no benefit to setting an event
coordinate for subsequent scroll events without a move event, and it lets us
avoid a potentially expensive GetFrameForPoint lookup.  This works because
scrolling views have widgets, so event coordinates anywhere within that widget
will give you the same scrolling view.

One thing I don't think we took into account is that we dispatch a
DOMMouseScroll event (in nsEventStateManager::DoWheelScroll).  This patch may
cause the target of that event to be incorrect; we should check whether that
breaks anything.  It looks like XUL trees, listboxes, and tooltips make use of
this event.  No DOM event spec mentions this event, however, IE does fire a
mousewheel event (see
http://msdn.microsoft.com/workshop/author/dhtml/reference/events/onmousewheel.asp )

I'd like to either get this in or decide that it's not a valid optimization and
wontfix it.