Follow-up Comment #5, bug #67544 (group groff): Using the program diffpdf I have created two pdfs using the same troff input but one using font TR and the second U-TR. The first image shows differences in the output, particularly the second half of the first paragraph, where U-TR manages to keep the word "Quisque" at the end of the line.
I then did the same runs again but added .kern 0 at the top of the file. Now
the files are visually identical since neither fonts are using their kerning
data.
I think this means that the meta-data in both fonts (at least the glyph widths
(the text example did not exercise the italic correction)) is sufficiently
close to not be visibly detectable.
Of course the actual glyph shapes are identical because the glyphs for both TR
and U-TR come from the same URW font. So, I did a third run, again no
kerning, but ne-TR.pdf produced via grops->ghostscript. This time there is a
visible difference - but not to the glyph shapes, just a very slight vertical
shift. This is likely to be a rounding issue, grops uses 2 decimals gropdf 3
decimals rounded, don't know what ghostscript uses. The fact it repeats every
4 lines points towards rounded calculation landing on pixel boundaries when
the glyphs are filled.
(file #58168, file #58169, file #58170)
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Additional Item Attachment:
Name: WithKern.png Size: 443KiB
<https://file.savannah.gnu.org/file/WithKern.png?file_id=58168>
Name: WithoutKern-grops.png Size: 323KiB
<https://file.savannah.gnu.org/file/WithoutKern-grops.png?file_id=58169>
Name: WithoutKern.png Size: 92KiB
<https://file.savannah.gnu.org/file/WithoutKern.png?file_id=58170>
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