Add information to detect Linux tablets/pens/styluses

Author: dacap

tablet.md

@@ -1,7 +1,9 @@
 # Tablet
 
+## Windows
+
 Since Windows 8, Microsoft introduced a new API to use your tablet
-with Windows program: the pointer API. Since Aseprite v1.2.19.1 you
+with Windows programs: the pointer API. Since Aseprite v1.2.19.1 you
 can configure what API do you prefer to use:
 
 ![Tablet section](tablet/tablet.png)
@@ -19,6 +21,36 @@ can configure what API do you prefer to use:
 Pressing the *OK*/*Apply* buttons will change the tablet settings
 immediately, there is no need to restart the program.
 
+## Linux/X11
+
+It looks like tablet/stylus/pen devices are detected by device
+name/brand name on X11, instead by device capabilities.
+
+There are some pre-defined IDs to detect a stylus, but it might not be
+enough (as it's indicated in
+[#3176](https://github.com/aseprite/aseprite/issues/3176))
+
+If Aseprite doesn't detect the pressure of your pen, since **Aseprite
+v1.2.35** you can try to do these steps:
+
+1. Close Aseprite
+2. Run `xinput --list` in a terminal/console
+3. Check the output and see what device could be the one related to
+   your stylus ([output example](https://github.com/aseprite/aseprite/issues/3176#issuecomment-1111799083))
+4. Open `aseprite.ini` file in the [preferences folder](preferences-folder.md)
+5. Search the `[general]` section and add the name of your stylus in a
+   `x11_stylus_id` option (the name must appears just like in the
+   first column of the `xinput --list` output):
+```
+[general]
+x11_stylus_id = Your Stylus Name
+```
+6. Save the file and start Aseprite
+
+Please inform us if this does work for your case adding a new comment
+in [#3176](https://github.com/aseprite/aseprite/issues/3176)
+indicating the name of your device.
+
 ---
 
 **SEE ALSO**

troubleshooting.md

@@ -25,7 +25,8 @@ In case of crash, you might be able to [recover some sprites](data-recovery.md).
 
 ## Tablet Problems
 
-In case your tablet doesn't work, please check the [tablet](tablet.md) page.
+In case your tablet (or the pressure of your tablet) doesn't work,
+please check the [tablet](tablet.md) page.
 
 ## macOS Rendering Problems