Re: eqn formatting issues with grops and gropdf

[G. Branden Robinson]

[replying to groff@ from bug-groff@ so more people see this discussion]

I wanted to make sure more people saw this because Deri's explanation is
gold.  I don't think there's any existing documentation that covers this
anywhere nearly as lucidly.

Regards,
Branden

At 2022-07-26T17:19:04+0100, Deri wrote:
> On Tuesday, 26 July 2022 09:00:25 BST joerg van den hoff wrote:
> > me again with an update/correction to the previous description of
> > the issue (the described problem remains, though):
> > 
> > 1.
> > regarding the symobl fonts used by grops and gropdf I previously
> > stated the former were using SS (symbols slanted) and the latter S
> > (symbols) which I presumed according to the looks of the greek
> > letters in the ps output (upright) and pdf output (slanted to the
> > right like italics). this was *wrong*. looking into the font
> > information in the formatted files it was the other way around
> > (grops was using SS and gropdf using S).
> > 
> > looking into the DESC files, I do find indeed entries
> > 
> > grops:  fonts 9 0 0 0 0 0 SS S ZD ZDR
> > gropdf: fonts 9 0 0 0 0 0 0 S ZD ZDR
> > 
> > which explains the font selection that occurred. I do not
> > understand, however, while this ultimately lead to _slanted_ glyphs
> > with gropdf and _upright_ glyphs with grops (exactly the other way
> > around as I would have expected for S vs SS).
> > 
> > 2.
> > forcing grops to also use S (by editing the DESC file and removing
> > SS from the entry) leads to sane ps and pdf output with both devices
> > (no misalignment and strange irregular widths of the greek letters).
> > so this would be the quick patch to "repair" grops: change the DESC
> > file.
> > 
> > 3.
> > using now the same font S, the glyphs produced by grops are upright
> > (expected) and those produced by gropdf are slanted (unexpected).
> > why is that??
> > 
> > the main observation remains unaltered: in standard setup grops uses
> > SS for typesetting greek letters since SS is found before S
> > according to DESC and this leads to rather massive typesetting
> > errors in equations using possibly many greek letters: cumulative
> > mispositioning of stuff later on the same line.
> > 
> > what do to about this?
> > 
> > thank you
> > joerg
> > 
> 
> Hi Joerg,
> 
> You are correct that gropdf does not include the SS font. The reason
> is because it is not a proper font, it is instead a postscript
> program, which, when run by a postscript interpreter such as
> ghostscript or a postscript printer, generates a slanted version of
> the symbol font. This is not valid as a pdf font.
> 
> The SS font and the S font both define *a but only S defines *A so
> when they are both loaded with .special SS S the lower case is found
> in SS but uppercase in S. Since gropdf does not have SS *a is found in
> S and a special command is sent to gropdf "x Slant 16" which tells it
> to slant the glyph by 16 degrees.
> 
> If you type:-
> 
> echo "\[*a]" | groff -Z
> 
> You will see:-
> 
> x T ps
> x res 72000 1 1
> x init
> p1
> x font 11 S
> f11
> s10000
> V12000
> H72000
> md
> DFd
> C*a
> h6310
> n12000 0
> x trailer
> V792000
> x stop
> 
> But if you type:-
> 
> echo "\[*a]" | groff -Tpdf -Z
> 
> It changes to:-
> 
> x T pdf
> x res 72000 1 1
> x init
> p1
> x font 11 S
> f11
> s10000
> x Slant 16
> V12000
> H72000
> md
> DFd
> C*a
> h6310

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