[NTG-context] Re: SPR: was Re: Re: language in tagging and export

16 Jul 2025

      Hi Hans (et al),

On Wed, Jul 16, 2025 at 08:33 (+0200), Hans Hagen via ntg-context wrote:
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On 7/16/2025 1:14 AM, Max Chernoff via ntg-context wrote:
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Hi Jim,
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On Tue, 2025-07-15 at 10:06 -0300, Jim wrote:
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Might I ask you
(a) To confirm that your PDF reader does, indeed, do SPR?
     (I.e., not just everything else on your system.)
and
...
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Ah, good point, I should have checked first. Using the following test
file:
...
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\loadtypescriptfile[plex]
...
...
\setupbodyfont[plex-thin, sans]
     \setupinterlinespace[1sp]
...
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\define[1]\makeline{%
         \setupbodyfont[#1pt]%
         \dorecurse{
             \numexpression(\textwidth / \widthofstring{l}) - 1\relax
         }{l\hfill}%
         \unskip%
         \par%
     }
...
...
\define\makelines{%
         \processcommalist[2, 4, 6, 8, 10, 11, 12, 16, 24, 36, 72]\makeline%
     }
...
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\startTEXpage[width=6in]
         \makelines
...
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\startframedtext[
offset=0pt,
width=broad,
background=color,
backgroundcolor=black,
color=white,
         ]
             \makelines
         \stopframedtext
     \stopTEXpage
...
...
Chromium and Firefox (pdf.js) use subpixel rendering, while Evince,
Okular, MuPDF, and xpdf just use greyscale antialiasing. I usually use
Firefox to view PDFs, and everything else on my system uses subpixel
rendering, so I just assumed that the rest of the PDF viewers did as
well.
...
all side effects of these pattents involved ... pathetic large company
policies ... esp given how trhey benefit from open source (and we're not
even talking stuff that can't be invented multiple times at the same place
independently)
Given "all" (most of) the other programs on my system (and, apparently,
Max's system) cheerfully do SPR, I don't believe that there are (for the
last 5 or 20 years, anyway) any patents encumbering PDF readers.

Rather, what I discovered when this problem first really started to annoy
me, at least according to what I read on the internet (so take what I write
here with a grain of salt!), some libraries used by Linux PDF readers
(reportedly pango, cairo and/or their bastard offspring pangocairo) just
aren't able to do sub-pixel rendering to the canvas upon which the PDF
output is drawn.

Why this restriction was there in the first place (maybe patents in the
last millennium?) I don't know.  Why the restriction has not been removed
is yet another thing I don't know.  Yet another place where my lack of
knowledge is both broad and deep. :-)

                                     Jim