It is planned to transition fltk to qt. A major problem in doing
this is that, for the same input, the resulting PDF bounding
boxes differ by a large enough amount that their use, for example,
in LaTeX \includegraphics() requires substantial recoding of the
parameters. It would be very useful if both plotting systems
produced the same plot, including Bounding Box values when
processing the same input. Here is an example of the surrent
state with and without -tight:

***********qt vs fltk Bounding Box results w/wo pdfcrop
                          qt                   fltk  
plot_diff.pdf            17 179 595 702     49 198 536 589
plot_diff-crop.pdf       0 0 578 523        0 0 487 391
plot_orig_norm.pdf       17 179 595 702     64 236 551 564
plot_orig_norm-crop.pdf  0 0 578 523        0 0 487 328

With -tight set:
plot_diff.pdf            17 179 595 702     52 200 551 600
plot_diff-crop.pdf       0 0 578 523        0 0 499 400
      

It would also be helpful to implement an option to run
pdfcrop before writing the output. -tight appears not to
do the same as pdfcrop. pdfcrop makes the plots easier to
use.