Commits on Dec 10, 2019

1. HACK: For speed, write out font styles only once. To elaborate: …

   **Background:** I had a few DVI files what were over 1000 pages long,
   on which dvisvgm would take hours to run.
   (Specifically, these files were the literate-programming listings of
   TeX/eTeX/pdfTeX/XeTeX programs, as typeset by WEAVE, except with each
   section on a separate page... but this situation may also be familiar
   to those trying to run dvisvgm on the TikZ manual, as in #x / #y .)
   
   With this change, the time to run dvisvgm went from hours to seconds.
   
   **What it does:** When invoked with certain options, for every page
   of the DVI file, dvisvgm writes out `@font-face` and text style CSS
   rules, like:
   
       @font-face{font-family:cmr10;src:url(data:application/x-font-ttf;base64,AAEAAAAN...
   
   and
   
       text.f12 {font-family:cmr10;font-size:9.96264px}
   
   All that this change does, in a hacky way, is accumulate these across
   pages, and write each of them only once. Then, the separate SVGs for
   each page can all just use the common style.
   
   **Caveats:**
   This is a giant hack, with MANY caveats:
   
   1. assuming there are enough pages (SVGs) for all this to be worth it,
   
   2. assuming only 7-bit fonts (having glyphs in positions 0 to 127),
   
   3. assuming font has no license problems (so doesn't have to be subset),
   
   4. assuming the user can do some postprocessing, namely generating CSS
      files by wrapping the `font-faces.txt` and `font-styles.txt` files
      within `<style>` tags.
   
   5. assuming SVG files don't have to be self-contained, i.e.
   
      - when used from a HTML page, will be inserted directly into the DOM and
        inherit its styles, rather than being wrapped in `img`/`object` tags
   
      - alternatively, postprocessing can put in the SVG file something like
   
               <style>@import 'common.css';</style>
   
        at the right place, where `common.css` is produced by (4) above.
   
   6. assming dvisvgm is being invoked something like this:
   
           dvisvgm --page=1- --font-format=woff2,autohint
   
   then, it *may* help to just do the expensive font-writing once, as here.

   

   shreevatsa committed Dec 10, 2019
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