Ruler can't be moved with gesture when under another item

[zepumph]

On the surface, this looks like the same sort of bug as with #201 (comment), but I think here we have something else.

First off, @terracoda sorry if there is another issue that embodies this bug. Let me know and we can combine.

The issue here is that the ordering of PDOM transforms isn't matching up in the same way as scene graph zlayer.

Notice how here in the picture the red mass and puller (ISLCObjectNode) has a highlight that extends onto the center of the ruler. To pick up the ruler, the pointer event is sent right to the number "5". The bug here seems to be that it get's intercepted by the ISLCObjectNode which seems to be on top of the ruler in the PDOM transform layer.

@jessegreenberg is there an easy way to confirm that this is the issue? Is there a way to keep the PDOM transform in z-layer in the same order as scene graph children?

[zepumph]

I'll add that when the ruler is in this position. I have not yet found a way to move it out of it at all.

[jessegreenberg]

I will look into further before making a general issue this issue because I don't understand it yet. It seems like this behavior contradicts what we determined in phetsims/scenery#1024. I would have expected that the ruler would always be picked up in this case because it's Node is on top of the sphere/puller in the scenery z-ordering.

[terracoda]

@zepumph and @jessegreenberg, I tested latest dev version 2.2.0-dev.21
and the sim seems to be working rather well with touch gestures and VoiceOver.

Here's my 2 cents in case you want it ;-)
I have some trouble swiping through content with cursor swipes, but I am not having trouble grabbing the ruler.

The case @zepumph points out is true: if the ruler is over the mass spheres, I have to be more careful to actually get my finger on the ruler. That said, I think it is better to have the mass spheres kind of override finding the ruler as the ruler is not so important. If I find and move focus to the ruler with cursor swipes, I can grab it if my double-tap and hold gesture does hit another interactive element. This seems ok to me, though we may need to keep a watch for issues related to layering.

[jessegreenberg]

OK thanks @terracoda!

I played with the sim for a few minutes and I haven't been able to get it to accidentally pick up the puller when the cursor is over the ruler. But that leaves the original issue where you can only select the puller with the virtual cursor if you tap in the area of the puller while the ruler is on top

From @terracoda's comment it sounds like this works out OK in this case but may cause problems in others. I will investigate in phetsims/scenery#1025 since work will happen there.

[jessegreenberg]

OK next steps for this issue were identified in phetsims/scenery#1025. We decided that it isn't necessary to address at this time because the ruler extends outside of the puller bounds and so can still be touched with VoiceOver outside of the puller area.

@zepumph can this issue be closed now?