8282702: Button is pressed one more time on Raspberry Pi with Touchscreen

[AlexanderScherbatiy]

Tapping on a button and next tapping on another place on the screen leads that the button is pressed twice on a Raspberry Pi with Touchscreen.

For example, run the JFXButtonExample app and first tap on the button in the left bottom side of the screen and second tap on the center of the screen.

This is a log of the state from LinuxStatefulMultiTouchProcessor.processEvents() method when System.out.printf("state: %s%n", state); code is added before the line: https://github.com/openjdk/jfx/blob/2e8a4a5e97bb88a5807ae5fe075b98e1d54a4ca0/modules/javafx.graphics/src/main/java/com/sun/glass/ui/monocle/LinuxStatefulMultiTouchProcessor.java#L140

state: TouchState[1,TouchState.Point[id=91,x=257,y=419]]
state: TouchState[1,TouchState.Point[id=91,x=257,y=420]]
state: TouchState[0]
Hello World!
state: TouchState[2,TouchState.Point[id=91,x=257,y=419],TouchState.Point[id=92,x=410,y=265]]
state: TouchState[2,TouchState.Point[id=91,x=257,y=419],TouchState.Point[id=92,x=409,y=267]]
state: TouchState[2,TouchState.Point[id=91,x=257,y=419],TouchState.Point[id=92,x=408,y=286]]
state: TouchState[0]
Hello World!

The TouchState contains only button coordinates (x=257,y=419) for the first tap on the button. The TouchState contains both the button coordinates (x=257,y=419) and coordinates of the center of screen (x=408,y=286) for the second tap on the center of the screen.

This happens because when LinuxStatefulMultiTouchProcessor.processEvents() pushes the state with current touches to the pipeline the LookaheadTouchFilter saves the current state and copies the previous saved state to the current state. https://github.com/openjdk/jfx/blob/2e8a4a5e97bb88a5807ae5fe075b98e1d54a4ca0/modules/javafx.graphics/src/main/java/com/sun/glass/ui/monocle/LookaheadTouchFilter.java#L74

That leads that the already deleted touch state (which contains the button coordinate) is restored.

The proposed solution is to put the copy of the touch state to the pipeline .

Printing the touch state after the fix shows the log:

state: TouchState[1,TouchState.Point[id=65,x=267,y=423]]
state: TouchState[1,TouchState.Point[id=65,x=269,y=425]]
state: TouchState[0]
Hello World!
state: TouchState[1,TouchState.Point[id=66,x=414,y=243]]
state: TouchState[1,TouchState.Point[id=66,x=414,y=238]]
state: TouchState[0]

The TouchState does not contains the button coordinates for the second tap.

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Issue

• JDK-8282702: Button is pressed one more time on Raspberry Pi with Touchscreen

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[kevinrushforth]

The fix looks OK to me. Since it is in Monocle, maybe @johanvos can review it?

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[AlexanderScherbatiy]

#641 proposes to fix the issue in general way in TouchPipeline, not only for LinuxStatefulMultiTouchProcessor.