Bug 64336 – RenderListBox scroller doesn't scroll

• Component: WebCore Misc.
• Status: NEW

[Joseph Pecoraro]

Existing test:
LayoutTests/platform/mac/fast/forms/listbox-scrollbar-hit-test.html

The test seems to succeed in DRT but the scrollbars don't work properly in Safari.
Scrollwheel events seem to work, but clicking on the scrollbar, using up/down etc
all don't work.

[Joseph Pecoraro]

Hmm, I see the "native animator" getting called, but ends up doing nothing:

    ScrollAnimatorMac::scroll...
    [m_scrollAnimationHelper.get() scrollToPoint:newPoint];

    gdb> po m_scrollAnimationHelper.get()
    <NSScrollAnimationHelper: 0x118616b50>

Because ScrollAnimatorMac::adjustScrollPositionIfNecessary resets the y scroll to 0:

    float newY = max<float>(min<float>(position.y(), m_scrollableArea->contentsSize().height() - m_scrollableArea->visibleHeight()), 0);
    => max(min(1, 125-129), 0)
    => max(min(1, -4), 0)
    => max(-1, 0)
    => 0

Is the "- m_scrollableArea->visibleHeight()" part of the equation necessary? It sounds like
we just want to clamp in the content size, in this case from 0 to 125 and the visible height
is not needed?

However, I think custom scrollers work. So I'll compare this to custom scrollers.

[Joseph Pecoraro]

This breaks whenever the visibleHeight is greater than the contentHeight.
So this is broken for custom scrollbars as well.

[Joseph Pecoraro]

Created attachment 100430 [details]
[PATCH] Proposed Fix

[Joseph Pecoraro]

Created attachment 100431 [details]
[PATCH] Proposed Fix

Now with git add ChangeLog!

[Sam Weinig]

Joe, do you know why this seems to work in DRT?

[Joseph Pecoraro]

Nope, I didn't look into that =/.

[Eric Seidel (no email)]

The difference between content and visible should be padding/margin, no?  We need some way to test this...

[Adele Peterson]

Would a test that used up/down work?

[Eric Seidel (no email)]

Comment on attachment 100431 [details]
[PATCH] Proposed Fix

r- for lack of test or lack of why testing is impossible/impratical.