Difficult to see some objects while dragging on iPhone

[samreid]

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Test device
iPhone 12

Operating System
iOS 16.1.2

Browser
Safari

Problem description
For phetsims/qa#870, while dragging the probe node in the 2nd screen, it is fully obscured by the finger and hence cannot be seen. Often for dragging things via touch, we will add a vertical offset so the item can be seen while dragging on a touch device. I saw a similar problem with dragging the track control points.

Steps to reproduce
See above.

Visuals

Troubleshooting information:
!!!!! DO NOT EDIT !!!!!
Name: ‪Energy Skate Park‬
URL: https://phet-dev.colorado.edu/html/energy-skate-park/1.2.0-rc.1/phet/energy-skate-park_all_phet.html
Version: 1.2.0-rc.1 2022-12-22 16:17:42 UTC
Features missing: applicationcache, applicationcache, touch
Flags: pixelRatioScaling
User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/108.0.0.0 Safari/537.36
Language: en-US
Window: 1440x704
Pixel Ratio: 2/1
WebGL: WebGL 1.0 (OpenGL ES 2.0 Chromium)
GLSL: WebGL GLSL ES 1.0 (OpenGL ES GLSL ES 1.0 Chromium)
Vendor: WebKit (WebKit WebGL)
Vertex: attribs: 16 varying: 31 uniform: 1024
Texture: size: 16384 imageUnits: 16 (vertex: 16, combined: 32)
Max viewport: 16384x16384
OES_texture_float: true
Dependencies JSON: {}

[arouinfar]

Thanks @samreid. Occlusion definitely looks like an issue in the image you shared. Luckily this sim supports pan and zoom, so that should do quite a bit to alleviate things. I compared ESP to a few other sims with a similar probe node (CCK, pH Scale, Waves Intro) and we aren't using the vertical offset in any of them.

@AgustinVallejo @samreid we can consider adding a vertical offset for touch, but I think we'll want to thoroughly test to make sure there aren't unintended bugs, especially since this doesn't seem like a common strategy for probes. I think the idea is worth exploring (if you'd like to), but I wouldn't consider it a necessary feature for this release.

[arouinfar]

I've given this more thought, and since the probe and control point behavior are no different from the published version (and other published sims) and pan/zoom mitigates the occlusion, I think we should skip this for the current release. I still think it's worth considering in the future, so I'll defer rather than close.