Hi Alicia,
I'll try to answer each question of yours in turn:
On Wed, Dec 27, 2017 at 1:20 PM, Alicia Boya <ntr...@gmail.com> wrote:
> Hi.
>
> I'm a bit sad that my Wacom tablet (CTH-670) is so poorly supported in
> gnome. The Wacom control panel does not recognize the stylus ("No stylus
> found", even when holding it on top of the tablet), two out of four express
> keys are incorrectly mapped as each other in the GUI and one is not even
> detected there.
>
> I can get everything working using xsetwacom in the terminal though. Is
> there any way I can improve this? I looked at /usr/share/libwacom but there
> are many things that I don't understand:
>
The Wacom panel within the GNOME Control Center has a few known issues
with Bamboo/Intuos devices. Most of these issues stem from differences
in how those devices appear to the system, compared to their
higher-end Cintiq/Intuos Pro cousins. Since most issues are with the
control panel rather than the drivers, you'll probably want to check
out https://bugzilla.gnome.org/
> For instance, where do the hexadecimal codes for the styli come from? How do
> I get one for my stylus? Are they arbitrary and I can't choose whatever
> integer or do they need to match a code coming from the hardware? How would
> I retrieve that code for my stylus?
>
Those particular hex codes are transmitted by some styli to the tablet
so that drivers and software can differentiate different types of
pens. Most tablets that only support a single kind of stylus (like the
CTH-670) don't report a hex code.
If a hex code is reported, the value for a particular type of pen can
be discovered either by examining the kernel event stream or the X11
device properties:
Kernel:
Run `sudo evemu-record | awk '/ABS_MISC/'` and select the pen device.
Bring the pen in and out of prox to see if any ABS_MISC events are
sent. The [decimal] number at the end of each line is this code.
X11:
Bring the pen in and out of prox, and then run `xinput list-props <id>
| grep "Wacom Serial IDs"` for the pen device. The third list item is
a [decimal] number corresponding to the code. Very small values (15 or
less) are "fake" IDs that the X driver creates for devices which don't
actually report a value. The value "2" in particular is used to mean
an unknown generic pen.
> Unlike some other .tablet files, bamboo-16fg-m-pt.tablet (the one for
> CTH-670) does not have a Styli property. May this be the cause the stylus is
> not recognized in gnome wacom settings?
>
The CTH-670 shouldn't report any stylus IDs (the "kernel" test above
shouldn't produce any output, and the "X11" test above should have "2"
for the third list item) so there shouldn't be a "Styli" line within
the tablet file. Its possible that the GNOME expects a styli line to
exist, but that would be a bug. Its also possible that some other bug
in GNOME is preventing the control panel from detecting the pen.
> Also the express keys: what is the relation between the button letters used
> in the `.tablet` files (A, B, C, etc.) and the numeric button numbers used
> in xsetwacom?
>
> I have noticed that in the case of my tablet buttons don't use sequential
> codes:
>
> (extract from my set-up-wacom.sh script)
> # pad buttons from top to bottom, with the hardware button number they emit
> PAD_1=1
> PAD_2=9
> PAD_3=8
> PAD_4=3
>
This is kinda difficult to explain, but I'll do my best:
libwacom uses letters (e.g. "A", "B", "C", "D", "E", etc.) to
represent physical buttons. A "layout" SVG defines where each of those
physical buttons exists on the tablet.
When a particular button is pressed, the kernel can send either
semantic button events (BTN_LEFT, BTN_RIGHT, BTN_FORWARD, BTN_BACK) or
generic button events (BTN_0, BTN_1, BTN_2, BTN_3, BTN_4, etc.)
depending on the tablet. Generally speaking, consumer tablets like the
CTH-670 send semantic events, while professional tablets send generic
events.
In response to a button event from the kernel, the X driver has to
translate it into a corresponding X button. X11 uses numbered button
events that have taken on semantic meaning over the years: 1 (left
click), 2 (middle click), 3 (right click), 4 (scroll up), 5 (scroll
down), 6 (scroll left), 7 (scroll right), 8 (navigate back), 9
(navigate forward), 10 (undefined), 11 (undefined), etc. For historic
reasons, our driver does not translate any button to buttons 4-7.
For your particular device, the libwacom layout file says that the
buttons A-D are arranged vertically from top to bottom. These buttons
send (BTN_LEFT, BTN_FORWARD, BTN_BACK, BTN_LEFT) from the kernel. The
X11 driver translates these to buttons 1, 9, 8, 3.
The GNOME Control Center doesn't (yet) properly support devices which
use semantic events, however. It assumes that tablets always send
generic buttons. Since your tablet has four buttons, this means that
it expects our driver to send X11 buttons 1, 2, 3, and 8. This is the
reason that buttons seem to be in the wrong location and why one of
the buttons isn't recognized by the control panel at all.
Press top button ("A") -> X11 button 1 sent -> GNOME thinks button "A"
Press next button ("B") -> X11 button 9 sent -> GNOME thinks no button
Press next button ("C") -> X11 button 8 sent -> GNOME thinks button "D"
Press bottom button ("D") -> X11 button 3 sent -> GNOME thinks button "C"
The very latest release of libwacom added an "EvdevCodes" setting to
the tablet files which explicitly states what kernel event each button
letter will send. GNOME doesn't use this information yet, but it
*could* use it to determine exactly which X11 button event to expect.
Once GNOME starts using this information, it should result in the
control panel recognizing all of the buttons in the right place.
BTW: I have a script at [1] which you can use to change the button
mappings of your tablet (either temporarily through xsetwacom, or
semi-permanently through xorg.conf.d) so that GNOME sees the buttons
it expects. Its helpful to work around this issue if you prefer to use
the GUI instead of xsetwacom all the time :)
[1]: https://gist.github.com/jigpu/fde784840ba5731726e7382952b0d5ed
Jason
---
Now instead of four in the eights place /
you’ve got three, ‘Cause you added one /
(That is to say, eight) to the two, /
But you can’t take seven from three, /
So you look at the sixty-fours....
> Regards.
> --
> Alicia.
>
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