not very clean, might be reworked at some point
the idea is to compute much less 'log' than what
was done

not very efficient, to be refined

requires those optimizations

is zero in get_dimensions for xy_plot

this calls clock_gettime for each active T macro, hopefully it
does not eat too much CPU

can be deactivated by commenting one line in T_defs.h

not tested

click at x/y refers to the toplevel window and the widget knows
its own x/y position, so let's keep the x/y of the click as is
and let the down widget handle translation by itself

something like that