Re: Jittery text in successive PostScript sequences

Paul Wessel <[email protected]> wrote:
> GMT (gmt.soest.hawaii.edu)uses PostScript to make maps and one
> application builds an animation from sequences of PostScript plots
> converted to PNG with ghostscript (9.22) and then to MP4 with
> ffmpeg.  We have found a problem that may be a ghostscript bug, or
> alternatively we are doing something wrong.  When using a rotating
> view (i.e., via a matrix concatenation to simulate different
> view azimuth (shown in TL corner) [here elevation is fixed at 90
> degrees], the resulting text strings "jitter" when viewed as a
> movie, i.e., the individual letters "dance".  For an example, see
> www.soest.hawaii.edu/pwessel/jittery.mp4.  As the movie plays,
> you will see the INDIVIDUAL letters in the word HELL jitter
> relative to each other, despite being set via a single show
> command ...

I am not 100% certain, but I _suspect_ that this is a consequence of
the individual character widths -- e.g. the result of

    (H) stringwidth pop

-- not coming out to an integral number of pixels in device space.
If so, one way to fix it might be to select the font and size so
as to achieve that property; clearly this would be easiest with a
monospaced font.  Granted that approach may be too limiting for the
effect you're trying to achieve.