diag_var(STRING* fmt,var);
Writes a variable into the acklog.txt file, controlled by a C-style
format string (see panel.digits). This instruction
can be used for logging fast-changing variables.
Example:
diag_var("\nframe: %6.3f",my.frame); // writes "frame: nnn.nnn" into acklog.txt.
See also:
-diag, diag, diag_frame, panel.digits