Tapping on a circle in the center of the screen sometimes generates mouse click events outside the circle with x coordinates set to zero.
To reproduce the issue run the [JFXCircle](https://bugs.openjdk.java.net/secure/attachment/98241/JFXCircle.java) sample. It has a circle in the center of the screen and a large rectangle under the circle which covers the whole screen. Tap quickly 10 times on the circle. The output is: circle mouse pressed [416.000000, 199.000000]: 1 circle mouse pressed [416.000000, 199.000000]: 2 circle mouse pressed [419.000000, 196.000000]: 3 circle mouse pressed [416.000000, 188.000000]: 4 circle mouse pressed [419.000000, 190.000000]: 5 rectangle mouse pressed [0.000000, 188.000000] circle mouse pressed [422.000000, 185.000000]: 6 circle mouse pressed [418.000000, 191.000000]: 7 circle mouse pressed [417.000000, 187.000000]: 8 circle mouse pressed [420.000000, 185.000000]: 9 circle mouse pressed [416.000000, 187.000000]: 10 circle mouse pressed [417.000000, 192.000000]: 11 circle mouse pressed [420.000000, 188.000000]: 12 One mouse event is reported by the rectangle with zero x coordinate. The issue occurs when one of ABS_MT_POSITION_X or Y position is not reported. For example, the output from `evtest /dev/input/event2` Event: time 1646845728.905383, -------------- SYN_REPORT ------------ Event: time 1646845728.935382, type 3 (EV_ABS), code 57 (ABS_MT_TRACKING_ID), value 1308 Event: time 1646845728.935382, type 3 (EV_ABS), code 53 (ABS_MT_POSITION_X), value 449 Event: time 1646845728.935382, type 3 (EV_ABS), code 54 (ABS_MT_POSITION_Y), value 240 Event: time 1646845728.935382, type 1 (EV_KEY), code 330 (BTN_TOUCH), value 1 Event: time 1646845728.935382, type 3 (EV_ABS), code 0 (ABS_X), value 449 Event: time 1646845728.935382, type 3 (EV_ABS), code 1 (ABS_Y), value 240 Event: time 1646845728.935382, -------------- SYN_REPORT ------------ Event: time 1646845729.025363, type 3 (EV_ABS), code 54 (ABS_MT_POSITION_Y), value 242 Event: time 1646845729.025363, type 3 (EV_ABS), code 1 (ABS_Y), value 242 Event: time 1646845729.025363, -------------- SYN_REPORT ------------ Event: time 1646845729.055379, type 3 (EV_ABS), code 57 (ABS_MT_TRACKING_ID), value -1 Event: time 1646845729.055379, type 1 (EV_KEY), code 330 (BTN_TOUCH), value 0 Event: time 1646845729.055379, -------------- SYN_REPORT ------------ The first SYN_REPORT reports ABS_MT_POSITION_X/Y [449, 240] coordinates. The second SYN_REPORT reports only ABS_MT_POSITION_Y value 242 and the ABS_MT_POSITION_X becomes undefined. As a result, the LinuxStatefulMultiTouchProcessor.updatePoint(x, y) method does not set the p.x value and it is left as zero. https://github.com/openjdk/jfx/blob/c6069d6845df4b90cca226e2b3dff49e3b48d8ac/modules/javafx.graphics/src/main/java/com/sun/glass/ui/monocle/LinuxStatefulMultiTouchProcessor.java#L161 The fix checks if ABS_MT_POSITION_X/Y value is undefined to use the previous ABS_MT_POSITION_X/Y value for the current slot. The first commit queries ABS_MT_SLOT maximum value to store slot IDs in an array. The second commit stores ABS_MT_POSITION_X/Y values in slotToX/Y values and uses them for current undefined values. ------------- Commit messages: - Use previous x/y values in case the current x/y values are undefined - Use ABS_MT_SLOT maximum value to store slots ids in array Changes: https://git.openjdk.java.net/jfx/pull/749/files Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=749&range=00 Issue: https://bugs.openjdk.java.net/browse/JDK-8282886 Stats: 26 lines in 1 file changed: 10 ins; 5 del; 11 mod Patch: https://git.openjdk.java.net/jfx/pull/749.diff Fetch: git fetch https://git.openjdk.java.net/jfx pull/749/head:pull/749 PR: https://git.openjdk.java.net/jfx/pull/749
