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tickbox var: $truncphaseflag -- for complex data
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default: 0 (FALSE)

The upper middle "truncph" tickbox (just under
the "MESH" button) toggles truncation of
complex-valued data by phase limits.

When $truncphaseflag is 1 ("truncph" is ticked),
only the phases within the interval specified in
the unlabeled entries on the next line are shown,
while phases outside the limits truncated to
background surface color.

The truncphase limits wrap.  For example:

  trunphasemin=0.3 truncphase=0.9
    => show phases between 0.3 and 0.9

  trunphasemin=0.9 truncphase=0.3
    => show phases between 0.9 and 1.0
    => show phases between 0.0 and 0.3

N.B.: the truncphase limits are applied *after*
the phase has been (optionally) adjusted by "rev"
(reverse time), "invph" (add half a cycle, which
equals multiply by -1), and "angleoffset"
(subtract arbitrary phase).

The tickbox immediately to the left labeled "sft"
controls $softtruncphaseflag, which linearly
ramps the cutoff edges to zero (see its R-click
help for details).
