Navigating the slides works perfectly with the Kensington PowerPointer for LibreOffice under Linux, no questions asked. The extra functions (“laserpointing”, drawing, and screen blanking) are not well supported. Here is how to fix them.

One of the supposed advantages of the Kensington PowerPointer over other devices such as the Logitech Presenter: No additional software is required. However, not all functions work out of the box, because they have to run through hoops to provide a zero-config experience for the majority of the users.

I invite you to follow my journey down into the Kensington (and Linux keyboard mapping; and, apparently, PowerPoint control compatibility) abyss.

PowerPoint Functionality

On PowerPoint, obviously everything works as expected. (No wonder, as the device was custom-made for Microsoft Office.)

Mode	Button	Duration	Function
⎚🚩 All	➡️ Forward	Any · —	⏩ Forward (autorepeat)
⎚🚩 All	⬅️ Back	Any · —	⏪ Backward (autorepeat)
⎚🚩 All	🔦 Laser	Long —	🚨 On-screen “laser”
⎚ Blanking	👤 User	Short ·	⬛ Black/contents (alternating)
⎚ Blanking	👤 User	Long —	⬜ White/contents (alternating)
🚩 Marking	👤 User	Short ·	⭕ Draw a circle
🚩 Marking	👤 User	Long —	📏 Draw a horizontal line
⎚🚩 All	🔦 Laser	Short ·	🗑️ Clear all marks

LibreOffice Functionality

As LibreOffice (and Linux) users, we are used that add-ons do not normally provide the full functionality (and sometimes the “full functionality” is beyond what any sane person would ever use…). So, I was pretty happy when Forward/Backward worked as announced; but the other functions didn’t work.

Mode	Button	Duration	Function
⎚🚩 All	➡️ Forward	Any · —	⏩ Forward (autorepeat)
⎚🚩 All	⬅️ Back	Any · —	⏪ Backward (autorepeat)

Of course, LibreOffice as of 7.4.7.2, doesn’t support the “virtual laser mode”. But everything else should be possible…

What happened?

As an investigative mind, I wondered why this could go wrong. With evtest, I was able to learn what sequences of HID events (keystrokes, mouse buttons) the device was sending.

Function	Button Sequence
⏩ Forward	Down
⏪ Backward	Up
🚨 “Fake laser”	Ctrl+LeftButton
⬛ Black/contents	Ctrl-H B and A Ctrl-U (alternating)
⬜ White/contents	Ctrl-H W and A Ctrl-U (alternating)
⭕ Draw circle	Ctrl-H [simulated move from center to top of circle] [simulated circular motion] Ctrl-P LeftClick LeftButtonDown [simulated circular motion] LeftButtonUp Ctrl-U [simulated move from top of circle to center]
📏 Draw horizontal line	Ctrl-P LeftButtonDown [horizontal component of user motion while the user is holding down the 👤 button] LeftButtonUp Ctrl-U
🗑️ Clear all marks	E+L+C (together!)

Some of this strikes me as strange:

Blanking: To blank LibreOffice with black or white, a single B or W keypress is sufficient. Any key (including repeating B or W) will unblank the screen. However, the PowerPointer sends two alternating sequences of two keypresses each; presumably to handle various incompatible pieces of presentation software.

Clear all marks seems to send multiple keystrokes for the same purpose. However, I was astonished to see that the keys are not pressed one after the other, as in the Blanking case above, but as three-key combo! (It seems to work.)

Drawing a circle is the strangest case. The mouse pointer is moved in a circular motion twice, the first time apparently without impact. Before the circle is actually painted (Ctrl-P, MouseDown, moving, MouseUp, Ctrl-U), an additional click of the left button is sent (highlighted in yellow above)! In LibreOffice, this advances to the next slide. As you will see below, this was a tough one to solve.

It looked like an unsolvable case: I would be stuck with just advancing the slides.

LibreOffice controls

What does LibreOffice provide?

Function	Keys and buttons
⏩ Forward	Down
⏪ Backward	Up
🚨 “Fake laser”	Not available
⬛ Black/contents	B (on); anything (off)
⬜ White/contents	W (on); anything (off)
⭕ Draw circle	P (toggle drawing mode); LeftButton (or MiddleButton(!)) to draw; optionally toggling drawing mode again
📏 Draw horizontal line	P (toggle drawing mode); LeftButton (or MiddleButton(!)) to draw; optionally toggling drawing mode again
🗑️ Clear all marks	E

Blanking the screen works kind of out of the box, mostly. Drawing a horizontal line also, kind of.

Note, that in LibreOffice, using the left mouse button for drawing will start drawing a new line. However, using the middle mouse button, it will set a flag that the next line will be a continuation of the current line (this is kind of like preventing the next moveto drawing command, so it will continue with lineto; i.e., everything will be a single line, even if you release the mouse button in between).

Managing expectations

Function	Events sent	Events expected
⏩ Forward	Down	Down
⏪ Backward	Up	Up
🚨 “Fake laser”	Ctrl+LeftButton	—
⬛ Black/contents	Ctrl-H B and A Ctrl-U (alternating)	B; anything
⬜ White/contents	Ctrl-H W and A Ctrl-U (alternating)	W; anything
⭕ Draw circle	Ctrl-H, Ctrl-P, LeftButton, Ctrl-U	P, LeftButton or MiddleButton; no LeftClick!
📏 Draw horizontal line	Ctrl-P, LeftButton, Ctrl-U	P, LeftButton or MiddleButton
🗑️ Clear all marks	E+L+C (together!)	E

Based on the above table, I came up with the following key/button mapping:

Key/button received	Key/button forwarded
Down, Up, A, B, P, W	as is
Ctrl	not needed → ignore
C, L, H	not needed/wanted → ignore
U	P
LeftButton	MiddleButton

Key	Keycode
Ctrl	KEYBOARD_KEY_700e0
A	KEYBOARD_KEY_70004
B	KEYBOARD_KEY_70005
C	KEYBOARD_KEY_70006
E	KEYBOARD_KEY_70008
H	KEYBOARD_KEY_7000b
L	KEYBOARD_KEY_7000f
P	KEYBOARD_KEY_70013
U	KEYBOARD_KEY_70018
Up	KEYBOARD_KEY_70051
Down	KEYBOARD_KEY_70052
LeftMouse	KEYBOARD_KEY_90001 (yes, “keyboard”!)

To activate this, put the following file in /etc/udev/hwdb.d/50-Kensington-PowerPointer.hwdb and then run systemd-hwdb update && udevadm trigger (or udevadm hwdb --update && udevadm trigger for non-systemd setups):

evdev:input:b0003v1EA7p0002*
 KEYBOARD_KEY_700e0=reserved   # Ctrl -> None
 KEYBOARD_KEY_70004=p          # A    -> P
 KEYBOARD_KEY_70006=reserved   # C    -> None
 KEYBOARD_KEY_7000b=reserved   # H    -> None
 KEYBOARD_KEY_7000f=reserved   # L    -> None
 KEYBOARD_KEY_70018=p          # U    -> None
 KEYBOARD_KEY_90001=btn_middle # Left -> Middle

Note:

• Indent the settings with exactly one space.
• Capitalization matters.
• Instead of reserved, unknown would also work (will work differently internally)
• Be aware that reloading the information, if you make changes, will not erase previous configuration information; it will only add to or replace it. To start from scratch, the easiest is to unplug/replug the Kensington USB dongle.

What have I done?

• To get around that ugly LeftClick, I mapped LeftMouse to MiddleMouse.
• To have MiddleMouse work, it needs to be surrounded by P. (Otherwise, all lines would be joined together. Also, we need to activate P (painting) mode anyway somewhere.) So we need to map U to P, so we have the “closing P“.
• But now, unblanking commands issue P as well, which we do not want. So we need to map A to P as well, to cancel the P created from the (original) Ctrl-U in the unblanking sequence.
• We don’t need Ctrl, C, H, and L, so we disable them (to avoid side-effects).

What works?

• Navigation works. I didn’t break it in the process. Whoa! (I would have liked long presses on the navigation keys to issue a different sequence, so I could have mapped it to PgUp/PgDown, to skip animations. Tough luck!)
• Drawing works, including erasing.
• Blanking works, but only every second time. (If you require blanking much more than drawing, remove the two mappings to the P key above (from the original A and U).
• Laser pointing does not work. LibreOffice does not yet provide the functionality. Maybe someone could try adapting Projecteur?

What have I learned?

1. A lot about udev, evtest and the handling of (HID) input events under Linux!
2. What hoops input devices have to go through when there is no driver/application waiting for just one key.
3. Auto-toggling buttons on remote controls are ugly.
4. Maybe everything would have been easier with a stateful approach, such as Interception Tools or a flexibility behemoth like KMonad. (I have tried neither of them.) Apparently, Projecteur also supports some of this. Anyone did this?
5. This ruleset could be extended to disable any other keycode that the device might send. (These cheap wireless channels have been used to inject keystrokes to attack computers; and the attack is not limited to keystrokes the device has keys for…)

Further reading

• Arch Linux Wiki: Keyboard input, accessed 2023-11-11.
  Background; overview over the entire process
• Arch Linux Wiki: Map scancodes to keycodes, accessed 2023-11-11.
  Detailed information about the udev mapping
• Arch Linux Wiki: Interception Tools, accessed 2023-11-11.
  If performing a 1:1 (or 1:0) mapping is not enough: More control over the input stream of a device
• KMonad, accessed 2023-11-11.
  Manage complex manipulations and keyboard layouts (also on Windows and OSX)