As we discussed, this means we only send the "button press" event, and never the "button release" event. So this should cause issues such as the text selection in micro to be triggered a lot more, right?

For me it fixes behaviour described in #1262 completely I do not experience selection triggering a lot more.

We discussed about sending "press" event in onDown() and "release" event in onUp(). However the function onDown() has a different signature and doesn't receive MotionEvent argument like onUp().

In the onUp() method we send two mouse events directly - mouse pressed and mouse released.

The byte sequence sent to the terminal from Termux, in the SGR scheme mostly used by programs now, should look like this:

0033  27 0x1B Escape '^[' or '\e'
0133  91 0x5B ASCII '['
0074  60 0x3C ASCII '<'
0060  48 0x30 ASCII '0'
0073  59 0x3B ASCII ';'
0065  53 0x35 ASCII '5'
0063  51 0x33 ASCII '3'
0073  59 0x3B ASCII ';'
0062  50 0x32 ASCII '2'
0061  49 0x31 ASCII '1'
0115  77 0x4D ASCII 'M'

0033  27 0x1B Escape '^[' or '\e'
0133  91 0x5B ASCII '['
0074  60 0x3C ASCII '<'
0060  48 0x30 ASCII '0'
0073  59 0x3B ASCII ';'
0065  53 0x35 ASCII '5'
0063  51 0x33 ASCII '3'
0073  59 0x3B ASCII ';'
0062  50 0x32 ASCII '2'
0061  49 0x31 ASCII '1'
0155 109 0x6D ASCII 'm'

where the format is (https://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h2-Mouse-Tracking):

SGR (1006)
          The normal mouse response is altered to use
          -   CSI < followed by semicolon-separated
          -   encoded button value,
          -   Px and Py ordinates and
          -   a final character which is M  for button press and m for button release.

This can be seen by executing vtshowkeys -m and touching the terminal.

Under tmux however, what the program (vtshowkeys) sees is often m (button release) coming before M (button press) - it seems that tmux (sometimes/quite often) reverses the order of these events. I don't know why that is.

An asciinema recording showing the issue:
https://asciinema.org/a/9RECJwPr2eVUN4NfwVun8nUUQ

I've created a tmux issue for it:
tmux/tmux#1931

UPDATE: Seems to be fixed in tmux master, to be included in the next tmux release (3.0). Backported to the Termux tmux package, at version 2.9a-5.

@xeffyr At least the text selection issue of micro under tmux is fixed after updating to version 2.9a-5 of tmux, right?

Well, that explains why issue was reproducible only under tmux. I'm closing pull request as latest update fixed it.