8282104: Node zoom/rotate flickers on Raspberry Pi with Touchscreen

[AlexanderScherbatiy]

Zoomed/Rotated with two fingers rectangle flickers (unexpectedly becomes pretty small or large and then returns back to previous size several times during zooming/rotating) on a Raspberry Pi with Touchscreen.

The log with traced events shows that it is possible that only one ABS_MT_POSITION_X or ABS_MT_POSITION_Y can be sent for a given slot. In this case the corresponding omitted Y/X value is undefined and is assigned from ABS_Y/X value. This produces incorrect result for slots different from 0.

Example of the trace events log, enabled by -Dmonocle.input.traceEvents.verbose=true -Dmonocle.input.traceEvents=true flags:

traceEvent: Processing EV_ABS ABS_MT_SLOT 1 [index=48]
traceEvent: Processing EV_ABS ABS_MT_TRACKING_ID 302 [index=64]
traceEvent: Processing EV_ABS ABS_MT_POSITION_X 399 [index=80]
traceEvent: Processing EV_ABS ABS_MT_POSITION_Y 272 [index=96]
traceEvent: Processing EV_KEY BTN_TOUCH 1 [index=112]
traceEvent: Read EV_ABS ABS_MT_SLOT 0 [index=176]
traceEvent: Read EV_ABS ABS_MT_POSITION_Y 315 [index=192]
traceEvent: Read EV_ABS ABS_Y 315 [index=208]
traceEvent: Read EV_SYN SYN_REPORT 0 [index=224]

...

traceEvent: Read EV_ABS ABS_MT_SLOT 1 [index=320]
traceEvent: Read EV_ABS ABS_MT_POSITION_Y 271 [index=336]
traceEvent: Read EV_ABS ABS_X 552 [index=352]
traceEvent: Read EV_ABS ABS_Y 322 [index=368]
traceEvent: Read EV_SYN SYN_REPORT 0 [index=384]

First both ABS_MT_POSITION_X/Y events with values x: 399 and y: 272 are received for the slot 1. Next only ABS_MT_POSITION_Y with y: 271 value is received (which implies that the x value has not been changed) for the slot 1. The x value is undefined in the LinuxStatefulMultiTouchProcessor.processEvents() loop and is unexpectedly assigned to the ABS_X 552 value which belongs to the slot 0.

The fix skips setting ABS_X/Y values for slots different from 0.

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Progress

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Issue

• JDK-8282104: Node zoom/rotate flickers on Raspberry Pi with Touchscreen

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Webrevs

• 00: Full (5b6348d8)

[kevinrushforth]

I see that this fix is limited to Monocle. Maybe @johanvos can review.

[AlexanderScherbatiy]

The fix also fixes the first use case described in the JDK-8087370

1. Consider you're touching the screen with two fingers, for example
coordinates of one point is ~100,100 and second point is ~200,200.
While still touching around the same points some events are reported with
one or another point to be either 100,200 or 200,100.

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[AlexanderScherbatiy]

@AlexanderScherbatiy This pull request has been inactive for more than 4 weeks and will be automatically closed if another 4 weeks passes without any activity. To avoid this, simply add a new comment to the pull request. Feel free to ask for assistance if you need help with progressing this pull request towards integration!

Could you review the simple fix?

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