498257 - video element below bottom of viewport causes overlong scrollbar

Status: RESOLVED DUPLICATE of bug 498593

(Core :: Layout, defect)

Description

[Matthew Gregan [:kinetik]]

Attachment: testcase

I noticed this in a wild at the above URL.  A simple testcase is attached, you may need to add more <br>s to cause the <video> element to end below the viewport.  As written, it works for me with a 900 pixel tall viewport.  Note that the width/height and background colour aren't necessary to reproduce, but make it easy to swap out for an <img> (where the problem doesn't occur).

Comment 1

[Matthew Gregan [:kinetik]]

Note that with my testcase, the scrollbar only moves as far as the visible document.  With the original bug URL, it moves beyond the end of the scrollbar trough.  And on one reload of the original URL, the scrollbar was fine, maybe affected by incremental layout?

Comment 2

[Matthew Gregan [:kinetik]]

I saw this happen at a page that doesn't contain a video element: http://community.livejournal.com/evan_tech/263952.html (the bug doesn't seem to happen very often on that page, so it's not a very good testcase).

I also tested the attached testcase on Windows 7 with a nightly build and saw similar behaviour, so it's not a Mac-only problem.

Debugging it on my Mac a little, it turns out that when the scrollbar is rendered incorrectly with the attached testcase, nsNativeThemeCocoa::GetScrollbarDrawInfo is using the default value for maxpos because the attribute isn't been set on the element.