xterm and 7-bit control codes
Ryan Johnson
ryanjohn@ece.cmu.edu
Thu Aug 12 14:50:00 GMT 2010
Hi all,
I'm running into a strange one...
At some point in the past (on linux because I didn't know about cygwin
yet), xterm used to send the following control sequence for a mouse
click at row 1, col 250
ESC [ M SPC \303\206 ! ESC [ M # \303\206 !
From what I could piece together, the formula for the x position was:
\40+x (x < 96)
\300+X/64 \200+X%64 (otherwise)
In other words, the first 96 characters were encoded as single octets,
with all later ones encoded as an octet pair.
I recently got back to using a wide monitor for the first time in years,
and discovered that my hacks to emacs' xterm-mouse-mode no longer worked
well because the two-octet code has been replaced by zero:
ESC [ M SPC \000 ! ESC [ M # \000 !
This makes it hard to use the mouse on the right side of a large
terminal window...
I've verified that it's not emacs doing this (nor bash) by running
directly (xterm -e) a small C utility which sends the mouse activation
sequence and then converts stdin to an octet stream. Mouse clicks arrive
just as emacs reported.
Am I smoking something or has something about this control sequence
changed in the last 5-6 years? I wonder if it has something to do with
UTF-8 handling and if X changed somehow...
The xfree86 control sequence documentation is less than helpful here
[1]. For "normal tracking mode" it says:
> On button press or release, xterm sends CSI M C b C x C y . The low
> two bits of C b encode button information: 0=MB1 pressed, 1=MB2
> pressed, 2=MB3 pressed, 3=release. The next three bits encode the
> modifiers which were down when the button was pressed and are added
> together: 4=Shift, 8=Meta, 16=Control. Note however that the shift and
> control bits are normally unavailable because xterm uses the control
> modifier with mouse for popup menus, and the shift modifier is used in
> the default translations for button events. The Meta modifier
> recognized by xterm is the mod1 mask, and is not necessarily the
> "Meta" key (see xmodmap). C x and C y are the x and y coordinates of
> the mouse event, encoded as in X10 mode.
In X10 mode:
> On button press, xterm sends CSI M C b C x C y (6 characters). C b is
> buttonâ1. C x and C y are the x and y coordinates of the mouse when
> the button was pressed.
I remember reading the same thing all those years ago and being annoyed
even then because it was so vague. Clearly the terminal was sending more
than 6 octets (who knows how many "characters" that's supposed to be),
and the spec doesn't mention the fact that all coordinates are offset by
\40. How UTF-8, Unicode, and other encoding complexities fit in I have
no clue...
This may turn out to have nothing to do with cygwin/X; if so I'd
appreciate ideas on where to send it next...
Ideas?
Ryan
[1] http://www.xfree86.org/current/ctlseqs.html#Mouse%20Tracking
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