RFR: 8252236: TabPane - initial select tab not working properly

[Ambarish Rapte]

On Thu, 10 Sep 2020 12:03:34 GMT, Jeanette Winzenburg <fastegal at openjdk.org> wrote:

> the issue is that the header of the selected tab is not always visible (or kept visible, see report for details)
> 
> - initially
> - after changing side
> - after resizing stage/tabPane
> 
> Fixed in TabPaneSkin to notify its TabHeaderArea (== collaborator that is responsible for layout the tabs) whenever its
> scroll might need an update.
> Added tests that fail before and pass after the fix.

In a bid to find more scenarios like you did mention description, I observed two more scenarios when selected tab does
not stay in view. 1. Inserting tabs before or removing tabs after selected tab or moving the selected tab, causes the
selected tab to go out of view. 2. Rotating TabPane can also take the selected tab out of view. I am little doubtful if
it a legitimate issue. The rotations I tried clipped TabPane and TabPane header.  I think rotation issue can be kept
out of scope of this issue, can be filed as a follow on. I leave to it to you to take a call.

About 1, I did quickly verify that it gets fixed by adding `invalidateScrollOffset();` call in
`TabHeaderArea.removeTab()`, `TabHeaderArea.addTab()` and  `TabHeaderArea.moveTab()`. Also If we fix it here, then bug
summary might need a change. It currently reflects only initial tab.

-------------

PR: https://git.openjdk.java.net/jfx/pull/300