16.5 Trace on the pick variables

  Tcl has the ``trace'' command which registers a procedure to be called when a variable is read, changed, or deleted. (Please see one of the various Tcl books for examples on how to use this.)

Since VMD sets the vmd_pick_atom and vmd_pick_mol variables, they can be traced.

 
• 16.5.1 Information about the picked atom
• 16.5.2 Making a sphere appear when an atom is picked
• 16.5.3 Drawing a line from the eye to the picked atom