Bug 19033 – Scrolling does not work when the mouse down is handled by a node

• Status: RESOLVED
• Resolution: FIXED
• Component: UI Events

[Ananta]

Launch Safari 3.1 and navigate to http://cn.msn.com
Wait for the page to load fully.
Now click on the vertical/horizontal scrollbars. 
Observe that the page does not scroll. It does scroll
with the mousewheel.

Debugged this and found that the mouse down event is handled by the 
node returned as a result of the hit test. The hit test does not have
a scrollbar associated with it. This causes the page to not scroll. 
The code should also check if there is a scrollbar under the mouse and
pass it off if yes. The webkit code already does this in the case when
the mouse down event is not handled.

Will submit a patch for this.

[Ananta]

Created attachment 21112 [details]
The patch containing the proposed fix for this issue.

[Ananta]

Comment on attachment 21112 [details]
The patch containing the proposed fix for this issue.

The patch has tabs in it. Will submit a new patch for review.

[Ananta]

Created attachment 21113 [details]
The patch containing the proposed fix for this issue.

[Darin Adler]

Comment on attachment 21113 [details]
The patch containing the proposed fix for this issue.

For this to get checked in, we'll need a test case demonstrating the problem, in the form of a regression test.

I can't tell from reading the patch alone if this is correct. The test case will both help me understand that there truly is a bug here, and also is required as part of our "all bug fixes must have a regression test" policy.

To simulate a mouse click, you can use the eventSender feature of the regression test engine. The test in fast/events/mousedown_in_scrollbar.html is an example of one that tests a mouse event in a scrollbar, and could be used as a starting point in making a test.

[Eric Seidel (no email)]

We still have this diff in our tree, and I'm not sure why.
http://www.corp.google.com/~dglazkov/merge/WebCore-page-EventHandler.cpp-before.html#difflib_chg_to58__1

[Eric Seidel (no email)]

My apologies.  This is the external URL:
http://build.chromium.org/merge/WebCore-page-EventHandler.cpp-before.html#difflib_chg_to106__2

[casey]

jQuery UI Dialog is affected by this issue: http://dev.jqueryui.com/ticket/4671

[Antonio Gomes]

I think the change looks ok (I am not a reviewer) since MouseEventWithHitTestResults does not set "scrollbar" when hit-testing a frame scrollbar, but only in-frame scrollbars (like scrollable <div>, <textarea>, etc).

(In reply to comment #3)
> Created an attachment (id=21113) [details]
> The patch containing the proposed fix for this issue.

However I could not reproduce the problem on Safari (webkit - trunk) on Snow Leonard. Given PLATFORM "WIN XP", I think it is Windows specific. Could you confirm?

[Antonio Gomes]

(In reply to comment #0)
> Launch Safari 3.1 and navigate to http://cn.msn.com
> Wait for the page to load fully.
> Now click on the vertical/horizontal scrollbars. 
> Observe that the page does not scroll. It does scroll
> with the mousewheel.

Safari seems to scroll the page ok now.

Please provide a (reduced) test case or a new URL that shows the bug  or it is not actionable.

> Debugged this and found that the mouse down event is handled by the 
> node returned as a result of the hit test. The hit test does not have
> a scrollbar associated with it. This causes the page to not scroll. 
> The code should also check if there is a scrollbar under the mouse and
> pass it off if yes. The webkit code already does this in the case when
> the mouse down event is not handled.
>

[Steven Wittens]

Created attachment 209805 [details]
Reduced test case

This bug is occurring on http://acko.net/ anywhere at the top. Debugging confirms a document mousedown handler fires when clicking the scrollbar. Emptying out the entire DOM does not fix this.

This is on Mac OS X, both with and without permanent scrollbars enabled. When using temporary scrollbars, you can also click the Gear button in the top right through the scrollbar.

I've attached a reduced test case. Note:

1) The scrollbar is unusable with the mouse
2) The grey div punches through the scrollbar for hit testing

Bug appears on Safari 6.0.5, Chrome 29, Chrome 31.

[Antonio Gomes]

Reproduced on Linux (webkit-gtk) and Mac/Safari. Taking..

[Antonio Gomes]

Created attachment 273008 [details]
Patch, no tests yet. For EWK

[Chris Dumez]

Comment on attachment 273008 [details]
Patch, no tests yet. For EWK

View in context: https://bugs.webkit.org/attachment.cgi?id=273008&action=review

I am not familiar with this code but have a couple of minor comments.

> Source/WebCore/page/EventHandler.cpp:1580
> +Scrollbar* scrollbarForMouseEvent(const MouseEventWithHitTestResults mouseEvent, FrameView* view)

const MouseEventWithHitTestResults&

> Source/WebCore/page/EventHandler.cpp:1582
> +    Scrollbar* scrollbar = nullptr;

Scrollbar* scrollbar = view ? view->scrollbarAtPoint(mouseEvent.event().position()) : nullptr;

[Chris Dumez]

Comment on attachment 273008 [details]
Patch, no tests yet. For EWK

View in context: https://bugs.webkit.org/attachment.cgi?id=273008&action=review

>> Source/WebCore/page/EventHandler.cpp:1580
>> +Scrollbar* scrollbarForMouseEvent(const MouseEventWithHitTestResults mouseEvent, FrameView* view)
> 
> const MouseEventWithHitTestResults&

also should be static.

[Antonio Gomes]

Created attachment 273012 [details]
Patch, no tests yet. For EWK (v2)

[WebKit Commit Bot]

Attachment 273012 [details] did not pass style-queue:


ERROR: Source/WebCore/ChangeLog:8:  You should remove the 'No new tests' and either add and list tests, or explain why no new tests were possible.  [changelog/nonewtests] [5]
Total errors found: 1 in 2 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[Antonio Gomes]

Created attachment 273032 [details]
Patch with tests (v1)

[Build Bot]

Comment on attachment 273032 [details]
Patch with tests (v1)

Attachment 273032 [details] did not pass mac-wk2-ews (mac-wk2):
Output: http://webkit-queues.webkit.org/results/923600

New failing tests:
fast/events/prevent-default-prevents-interaction-with-scrollbars.html

[Build Bot]

Created attachment 273040 [details]
Archive of layout-test-results from ews106 for mac-yosemite-wk2

The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews.
Bot: ews106  Port: mac-yosemite-wk2  Platform: Mac OS X 10.10.5

[Antonio Gomes]

Created attachment 273084 [details]
Patch with tests (v2)

Attempt to make the test run on EWK-Mac2.

[Build Bot]

Comment on attachment 273084 [details]
Patch with tests (v2)

Attachment 273084 [details] did not pass mac-wk2-ews (mac-wk2):
Output: http://webkit-queues.webkit.org/results/927157

New failing tests:
fast/events/prevent-default-prevents-interaction-with-scrollbars.html

[Build Bot]

Created attachment 273085 [details]
Archive of layout-test-results from ews105 for mac-yosemite-wk2

The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews.
Bot: ews105  Port: mac-yosemite-wk2  Platform: Mac OS X 10.10.5

[Antonio Gomes]

Created attachment 273196 [details]
Patch with tests (v3)

[Antonio Gomes]

Adding Simon/Beth/Darin, which I believe are familiar with this code.

This is a simple fix, that affect real world websites, and differ WebKit from Gecko/Blink these days.

[Antonio Gomes]

Created attachment 273295 [details]
Patch with tests (v3.1)

Rebased against ToT, fixed typos on WebCore/ChangeLog.

[Darin Adler]

Comment on attachment 273295 [details]
Patch with tests (v3.1)

View in context: https://bugs.webkit.org/attachment.cgi?id=273295&action=review

> Source/WebCore/page/EventHandler.cpp:1585
> +    Scrollbar* scrollbar = view ? view->scrollbarAtPoint(mouseEvent.event().position()) : nullptr;
> +    if (!scrollbar)
> +        scrollbar = mouseEvent.scrollbar();
> +    return scrollbar;

Now that this is factored out into a function, it can be refactored to make the logic slightly clearer. Like this, perhaps.

    if (view) {
        if (auto* scrollbar = view->scrollbarAtPoint(mouseEvent.event().position()))
            return scrollbar;
    }
    return mouseEvent.scrollbar();

[Antonio Gomes]

Created attachment 273303 [details]
Patch for landing.

[Antonio Gomes]

(In reply to comment #26)
> Comment on attachment 273295 [details]
> Patch with tests (v3.1)
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=273295&action=review
> 
> > Source/WebCore/page/EventHandler.cpp:1585
> > +    Scrollbar* scrollbar = view ? view->scrollbarAtPoint(mouseEvent.event().position()) : nullptr;
> > +    if (!scrollbar)
> > +        scrollbar = mouseEvent.scrollbar();
> > +    return scrollbar;
> 
> Now that this is factored out into a function, it can be refactored to make
> the logic slightly clearer. Like this, perhaps.
> 
>     if (view) {
>         if (auto* scrollbar =
> view->scrollbarAtPoint(mouseEvent.event().position()))
>             return scrollbar;
>     }
>     return mouseEvent.scrollbar();

Sounds good, done.

[WebKit Commit Bot]

The commit-queue encountered the following flaky tests while processing attachment 273303 [details]:

http/tests/xmlhttprequest/workers/xmlhttprequest-file-not-found.html bug 155176 (authors: [e-mail] and [e-mail])
The commit-queue is continuing to process your patch.

[WebKit Commit Bot]

Comment on attachment 273303 [details]
Patch for landing.

Clearing flags on attachment: 273303

Committed r197784: <http://trac.webkit.org/changeset/197784>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.