Alarm tree display broken as side effect of configurable background color

[kasemir]

#2449 added configurable background colors based on alarm severity to the alarm tree, alarm table, PV tree etc.

Turns out that broke the alarm tree display.

The tree view had a small triangle to the left of intermediate nodes that allow opening/closing the sub tree, and the background was used to indicate the selected cell when clicking on a cell or traversing the three using cursor keys:

Now that the tree cell backgrounds are set based on the alarm colors, clicking on "Demo" in the above example will remove(!) that expand/collapse triangle, and there is no more visual feedback of the selected item:

That was actually a known caveat because I guess using setBackground had been tried before,

phoebus/app/alarm/ui/src/main/java/org/phoebus/applications/alarm/ui/tree/AlarmTreeViewCell.java

Line 33 in cc28ab9

// Note: Cannot use background because that's used by style sheet and selection/cursor

        // Note: Cannot use background because that's used by style sheet and selection/cursor

[shroffk]

Sorry,
I should have paid more attention to the comments.

The initial attempt to implement the background was to set the sytle sheet ( I have added a TODO about this ) however this did not work. Once I am back in a few weeks I will try to redo this feature using the style sheet... hopefully the move to the latest javafx might have addresses the issues I was facing in the past.

[georgweiss]

Speaking of latest JavaFX... If you mean v 20 then we need to bring up Java version.

[kasemir]

I tried this with JFX 20 and there was no difference in the alarm tree.
The modena.css for the tree simply includes changes to the background for the selection/cursor, and it also uses the background for the 'arrow', so setting the cell background clashes with that.
The fix on the branch is to have our own Label or HBox(Icon, Label) and then you can update the background of that Label while the tree can continue to do what it wants with the overall background.

[shroffk]

Thank you for fixing this @kasemir

When I suggested the redoing this I was planning of replacing the programmatic background sets with calls to set the css -fx-control-inner-background, which should hopefully work more consistently with the rest of the widgets behaviours.

Anyway, your solution might be simpler and cleaner so we should keep that

[kasemir]

The missing expand/collapse triangle was minor, what really caused trouble is the missing cell updates, #2611
I was looking at that when I noticed this issue.

I think it's quite common that you have some section of the alarm tree open with many PVs, only partially visible because the list exceeds the window height, and then those that are not shown end up with the wrong value once scrolled into the viewport. I can reproduce that with a simple demo that suggests TreeItem.setValue() simply doesn't always work, you need to replace the TreeItem. Fixed that in #2615, but now overall disenchanted with the TreeView.