Avoid transitioning from pinch until all fingers have been released.

[puckey]

This fixes issue #6478:

• pinch end is triggered only when both fingers are released
• down trigger only happens if we aren't pinching

[cesium-concierge]

@puckey, thanks for the pull request! Maintainers, we have a signed CLA from @puckey, so you can review this at any time.

⚠️ I noticed that CHANGES.md has not been updated. If this change updates the public API in any way, fixes a bug, or makes any non-trivial update, please add a bullet point to CHANGES.md and comment on this pull request so we know it was updated. For more info, see the Pull Request Guidelines.

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[hpinkos]

Thanks @puckey! @emackey can you review?

[pjcozzi]

@puckey thanks again for the pull request!

@emackey is this something you can look at? It is only a few lines of code.

[emackey]

I do, sorry for the delay. I need to carve out a bit of time to try this on a touchscreen.

[emackey]

Thanks @puckey, this is certainly better behavior for the user. You've got one failing unit test, and I'm curious which strategy you'll take in fixing it. Also can you merge master into here when you get a chance? Thanks!

[emackey]

This test fails, and indeed PINCH_START is re-called when the user's touch count deviates from 2 (while remaining non-zero) and returns to 2, bringing pinch out of suspension. I'm not sure this is a bad thing, as the pinch is re-starting even though it never fully stopped.

Anyway the test should be fixed, not sure if by changing the test's expectation or by suppressing the pinch re-start event.

[puckey]

Thanks – I will look into this next week!

[puckey]

Since we aren't firing PINCH_END with a single touch up, it indeed doesn't make sense to fire PINCH_START when moving back to 2 fingers down.

I added a check to see if we are already pinching when touch count returns to 0.. All tests should be green and I merged in master.

[emackey]

Thanks @puckey. I will test on a touchscreen soon. With the latest changes I'd like to make sure that if I have two fingers down, and I lift one finger and place it down somewhere new, I don't get a sudden jump as if I had moved the finger from one place to the other. That my concern with skipping the intermediate PINCH_START event, but I'm not sure if it will happen.

[puckey]

Yes, I had the same concern.. I built the demo to check this on my iPhone and it seemed fine – but another check is always a good idea!

[emackey]

Code looks good, tests pass, behavior seems nice on a touchscreen. Great work @puckey.

[emackey]

Updated CHANGES.md in a32d774.