[NTG-pdftex] vf font expansion bug

Hello Thanh (please ack :), and everyone else - Robert (cc'd) recently reported an "interesting" pdftex bug related to font expansion of vf files on the tex-live list. For the record, his original report is here: https://tug.org/pipermail/tex-live/2020-March/045099.html but I'll quote as needed to make this email self-contained. Sorry, it's unavoidably long. I have a proposed fix (at the end) and am hoping for some kind of confirmation that it makes sense. (I am definitely not planning to make any change here for TL20. It's not that urgent, and testing is needed.) So, Robert found a case where pdftex mixes up two expanded fonts, when virtual fonts are involved. Here is a test file vfexp.tex, slightly modified from his original so it will run with -ini: ----------------------------------------------------------------------------- \catcode`\{=1 \catcode`\}=2 \pdfoutput=1 \nonstopmode \hbadness=10000 \vsize=20pc \hsize=30pt \parfillskip=0pt plus1fil \font\1=cmr10 \font\2=bchr8t %\font\2=bchr8r \pdfmapfile{} \pdfmapline{+cmr10 CMR10 0) then + {Find stretch and shrink values, if any.} + if pdf_font_stretch[f] = null_font then stretch_limit := 0 + else stretch_limit := pdf_font_expand_ratio[pdf_font_stretch[f]]; + {Ditto for shrink.} + if pdf_font_shrink[f] = null_font then shrink_limit := 0 + else shrink_limit := pdf_font_expand_ratio[pdf_font_stretch[f]]; + {Now make the font(s) for |k|.} set_expand_params(k, pdf_font_auto_expand[f], - pdf_font_expand_ratio[pdf_font_stretch[f]], - -pdf_font_expand_ratio[pdf_font_shrink[f]], + stretch_limit, + -shrink_limit, pdf_font_step[f], pdf_font_expand_ratio[f]); vf_def_font := k; end;