Fall back to linear initial velocity if there's not enough samples for inertia #14961
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What does the pull request do?
Fallbacks to linear scroll velocity if not enough touchpoints have been registered in a swipe for polynomial computation of inertia.
This also adds a touch point at pointer press to the velocity tracker to ensure start and end points of the swipe are accounted for in the tracker.
What is the current behavior?
Some mobile os and devices have reduced touch polling rate when no activity is detected on screen, or as a power saving measure. Because of this, a flick on the screen could be faster than the os can send event that, our tracker would only register 1 or 2 pointer move events. With so few points being register in that gesture, the tracker returns 0 for inertia, even though the user has completed a swipe.
What is the updated/expected behavior with this PR?
A quick flick on a touch screen will be detected as a scroll swipe.
How was the solution implemented (if it's not obvious)?
Since we are guaranteed a PointerPressed if a user touches the screen, we register that point as the first point(0,0) in the tracker. If a swipe is done, this will add another point to the tracker on PointerMoved. If no more pointer move event are sent, we have at least 2 points to calculate the velocity of the fling when the pointer is released.
Checklist
Breaking changes
Obsoletions / Deprecations
Fixed issues
Fixes #14919