Emulating a laser pointer over X windows

Nowadays it also occurs sometimes to make the presentation in a videoconference. In this case one cannot use a laser pointer, so I looked for a way to have something like a bright and large screen cursor which I could move around the screen with my local mouse.

I therefore need a way to

• generate the icons
• start the application iconized (ideally at the current mouse cursor position) (i.e. turning the laser pointer on)
• move the icon around
• stop the application (i.e. turning the laser pointer off)
• eventually change the icon (e.g. from a simple pointer to a circle or ellipse surrounding a word)
• eventually park the icon in some corner of the screen
• the icon shall of course stay on top of all other windows
  and its mouse operation shall not interfere with the normal usage of the mouse or keyboard (e.g. click to advance slides in the presentation, or to follow an URL)

Implementation

• The only items which may possible require downloading are the icons (unless you want to create your own). These are the three sample icons I use in their natural size. Just use your browser to retrieve them.

  100×100 pix circle	200×100 pix ellipse	80×80 pix "laser beam"

  The icon files shall be stored in some directory, like a place where you keep other personal icons, or the directory where the .fvwm2rc configuration file is.

• The remainder of the "installation" just consist in copying lines into the .fvwm2rc configuration file.

• The next step is to make fvwm aware of such directory which is achieved just making sure it is appended to the ImagePath line in the .fvwm2rc configuration file.
  ImagePath .....:/<yourdirectorypath>

• The next step is to choose the application (I use xterm), and to associate one of the icons to it. One has also to define the command used to start the application.
  I start the application iconified, and with a special name resource, which in fvwm can be achieved with a run string like Exec xterm -name Laser -iconic

• In order to make sure the icon stays always on top of all other windows on all desktops, has no associated title but just the icon, is not parked in an eventual icon box but is created at the mouse position in my case I use a particular style LaserBase defined in .fvwm2rc.
  The example works starting from my pre-existing .fvwm2rc. Tuning might be necessary in your case.

  The potential styles LaserA LaserB LaserC are de facto not used but just define the possible association of the three icons. The only usage is in the next line. I give all three styles to allow you to choose a default.

  The style Laser is initialized to one of those and associates the (default) icon to the application exploiting the name resource.

  This is the relevant bit of .fvwm2rc:

  Style LaserBase StickyIcon, StickyAcrossDesks, Layer 9, !IconTitle, IconBox none, PositionPlacement UnderMouse
  Style LaserA Icon beam.png,  UseStyle LaserBase
  Style LaserB Icon circle.png,  UseStyle LaserBase
  Style LaserC Icon ellipse.png, UseStyle LaserBase
  Style Laser UseStyle LaserA

• To start the application from the root menu add this to the definition of it in .fvwm2rc:
  + "LaserPointer " Exec xterm -name Laser -iconic

• The rest of this stuff can all be grouped together at the end of your .fvwm2rc:

• This sequence of lines defines a "laser switch on" function which can, if called with an argument equal to A, B or C, start a pointer with the shape defined by the style LaserA LaserB LaserC or otherwise by the current Laser style.
  DestroyFunc PointLaser
  AddToFunc PointLaser
    + I Exec xterm -name Laser$0 -iconic

• As example, a line like this associates a default startup to shifted mouse button 1
  Mouse 1 A S PointLaser
  while a line like this associates a startup with the laser beam icon to key P when pressed in the root window
  Key P R A PointLaser A
  None of these lines is mandatory.

• Defining a function key for laser switch on at current mouse position is definitely trickier.
  One has first to define an auxiliary function which moves the newly created icon to the current mouse position, offset by half of the icon sizes (so that it is centered), and associates the particular icon. The function requires three pseudo-arguments passed via environment variables.
  DestroyFunc rePointLaser
  AddToFunc rePointLaser
    + I ThisWindow ("Laser*") Move m-$[xof]p m-$[yof]p
    + I ThisWindow ("Laser*") WindowStyle Icon $[ik].png
    + I UnsetEnv xof
    + I UnsetEnv yof
    + I UnsetEnv ik

  One has then to associate an event handler to activate the function when a new icon is created

  DestroyModuleConfig Event-PL: *
  *Event-PL: Cmd Function
  *Event-PL: add_window rePointLaser

  Finally one can bind to a functional key the function with specific arguments. In our case we use shift-F4/5/6 and start all instances with the Laser style.

  PointerKey F4 A S PipeRead 'echo "SetEnv xof 50"   && echo "SetEnv yof 50" && echo "SetEnv ik circle"   && echo "PointLaser "'
  PointerKey F5 A S PipeRead 'echo "SetEnv xof 100" && echo "SetEnv yof 50" && echo "SetEnv ik ellipse" && echo "PointLaser "'
  PointerKey F6 A S PipeRead 'echo "SetEnv xof 40"   && echo "SetEnv yof 40" && echo "SetEnv ik beam"   && echo "PointLaser "'

• The definition of function keys to change icon with unshifted F4/F5/F6 is much simpler and operates on any instance due to the wildchar style
  PointerKey (Laser*) F4 I N WindowStyle Icon circle.png
  PointerKey (Laser*) F5 I N WindowStyle Icon ellipse.png
  PointerKey (Laser*) F6 I N WindowStyle Icon beam.png

• The definition of function keys to move, park and switch off with unshifted F1/2/3 is even simpler
  PointerKey (Laser*) F1 I N Move
  PointerKey (Laser*) F2 I N Move -0 -0
  PointerKey (Laser*) F3 I N Close

Bugs

The way I handle styles is possibly clumsy.

Contacts

Acknowledgment