Problems with .chart-plot-background and event handlers

Question

Hello. I'm trying to add event handlers to my chart so that the user can be allowed click within the chart itself to perform certain actions like dragging, zooming, etc. To avoid having to deal with handling mouse clicks that lie outside the chart itself (for example on the axes), I've found that:
.chart-plot-background
is the Region that gives me the entire chart and nothing else. However, when I attach mouse listeners to this Region, the event is only registered on half of the cells in the chart. If you've seen the default JavaFX Chart background layout, you know that it contains alternating rows of cells with slightly different coloring. I've found that only the rows with the lightest gray coloring actually register a mouse click on them, which makes me believe the dark grey cells are not part of the .chart-plot-background, but something else on top.
To me, this feels like an oversight in how the regions of the chart are defined. Why can I not get a listener to work on the whole chart and nothing else? Currently the only workaround seems to be to take the Region:
.chart-content
instead, and compute the difference between this region and the .chart-plot-background in order to manually suppress mouse clicks that lie outside .chart-plot-background.
Anyone have suggestions? Is this worth issuing on the JavaFX Jira?

Answer 1

Hello,
I'm not an expert on controls, but here is my guess based on your description: when you register an event handler on a "background" node, it is called only when the mouse hovers over the background node - I suppose the light gray is the background with the light gray cells being transparent and dark grey cells being filled. So the behavior seems correct - you can't expect the events to be delivered to background when it is covered by other nodes. I think you really should register the handler on the entire chart and filter out the events you don't want to handle. This however should not require much of computing the difference between the regions, it should be possible to do just something like
if (!background.contains(event.getX(), event.getY())) {
    return;
Provided that the background doesn't reach under the axes as well. Note that if there are any different transforms between the background and the node with the handler registered on it, you may need to recompute the coordinates by
background.sceneToLocal(event.getSceneX(), event.getSceneY());
And use the contains method on that.