Splotch size can be vastly exaggerated after many balloons hit at once

[phet-steele]

@jonathanolson don't feel like you have to fix this since it is a devious multitouch.

1. Go to the paint on the explore screen.
2. Use finger A to fire and hold increasing a color, then a second later use finger B to fire and hold decreasing the same spinner. This should allow you to achieve endless balloons and paint dripping for that particular spinner. Do not release these fingers ever.
3. Use finger C to switch screens/scenes.
4. Wait as long as desired, maybe like 10 seconds?
5. Use finger C to switch back to the paint on the explore screen. The balloons will have "queued" and all hit at once to make the splotch gigantic.

Usually this is self correcting and a large amount of paint will drip out quickly afterward, but sometimes paint dripped does not equal balloons thrown so you get a large splotch stuck on screen. Decreasing to 0,0 will also not remove the splotch. You must refresh/reset.

Right splotch at 0,0

Seen on iPad Air 2 iOS 10.3.1 Safari. For phetsims/tasks/issues/839.
URL: http://www.colorado.edu/physics/phet/dev/html/proportion-playground/1.0.0-rc.1/proportion-playground_en.html
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[jonathanolson]

Multitouch not technically needed, the spinner just needs to alternate quickly enough.

Caused because when balloons hit, they instantly add splotch area, but drips don't instantly take it away (slowly drains from the splotch). So if you hit 100 balloons at approximately the same time as 100 drips start, the splotch size shoots up for a short period until the drips "drain" the splotch to the correct size.

[jonathanolson]

Pushed a potential fix (for the more permanent bug) and a workaround (for the temporary amount of paint exceeding the normally permitted size).

@amanda-phet, does this workaround seem acceptable?

[jonathanolson]

@phet-steele reported the potential fix didn't work.

I'll need to map out all of the logic and try to prove it's not possible (to see where the buggy code is).

[ariel-phet]

@jonathanolson this multitouch bug is not a concern and does not need to be fixed for publication

[jonathanolson]

But it is not a multi-touch bug as noted above?

[ariel-phet]

@jonathanolson is there any way to cause it without multitouch? If it is straightforward to fix, go ahead, but if it is a tricky fix and a highly unlikely user scenario it can be deferred

[jonathanolson]

Tricky(ish) to identify the fix, probably a very simple fix. Mean time for identifying is probably an hour.

Defer and do another RC?

[ariel-phet]

@jonathanolson yes please, defer and do another RC

[jonathanolson]

Commit above makes this probably harder to occur, as it interrupts input on the non-active scene when switching.