Possible to get floating soccer balls

[KatieWoe]

Test device
Dell
Operating System
Win 11
Browser
Chrome
Problem description
For phetsims/qa#781. Seen when using ?speed=.1 but it may be possible, if hard, during normal use.
When a soccer ball is about to land in a spot, dragging another on/off that spot as it lands can cause the positions to overlap, making it look like a ball is floating and/or missing. This requires precise timing and luck, even with the sim slowed down, so I'm not sure how likely it is during normal use.
Steps to reproduce

1. Use the query parameter ?speed=.1
2. One the first screen, use the kick 5 button
3. When one ball lands, drag it to where the next ball will land
4. As the second ball lands drop the first
5. It may also happen if you pick up the first ball from the landing spot as the second lands
6. This may take several tries

Visuals

Troubleshooting information:

!!!!! DO NOT EDIT !!!!!
Name: ‪Center and Spread‬
URL: https://phet-dev.colorado.edu/html/center-and-spread/1.0.0-dev.11/phet/center-and-spread_all_phet.html
Version: 1.0.0-dev.11 2022-03-07 01:50:02 UTC
Features missing: applicationcache, applicationcache, touch
Flags: pixelRatioScaling
User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/98.0.4758.102 Safari/537.36
Language: en-US
Window: 1280x649
Pixel Ratio: 1.5/1
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: 30 uniform: 4096
Texture: size: 16384 imageUnits: 16 (vertex: 16, combined: 32)
Max viewport: 32767x32767
OES_texture_float: true
Dependencies JSON: {}

[amanda-phet]

I've wondered if this might happen, but wasn't fast enough to make it happen on my own (and didn't know about the speed qp). I think this is a potentially strange issue if someone is just moving balls around and not trying to make it happen, so it would be helpful to think through a solution sooner rather than later, if possible.

[KatieWoe]

As a data point, I managed to reproduce this in phetsims/qa#795 without the speed parameter.

[samreid]

Good discovery! @amanda-phet would you recommend investigation into this for the current milestone?

[amanda-phet]

I think we can keep this on the 1.1 milestone.

[samreid]

@amanda-phet and @catherinecarter is the right kind of solution to investigate: when a ball is moved, detect if there are any floating soccer balls, and animate them to the ground?

[catherinecarter]

If there's a way to do that, your proposition seems best. We'd need to consider when there is a stack of floating balls like in the 2nd image above (two balls are stacked) and make sure to move the entire stack down.

[samreid]

I have seen this bug more and more after recent refactorings.

[samreid]

Even after other changes, this is still buggy by the instructions above (drag lower ball away while landed ball animating up)

[samreid]

Fixed and ready for review. After reviewing and discussing the commits, let's reassign to @KatieWoe for testing.

[samreid]

I'm still seeing problems on multikicks.

[samreid]

The recent commits seem to help a lot. I also opened a side issue. Probably ready for review again?

[samreid]

Today I got a floating soccer ball by dragging one from a stack while a ball was animating up the stack. Maybe also be tested in #188

[matthew-blackman]

There is some buggy behavior here, but I'm no longer able to get floating soccer balls. Continuing this in #188

[samreid]

@marlitas can this issue be closed?

[marlitas]

Closing as completed.