properly handle SVGs generated by SVGMath

[akavel]

For #220, it would be nice if SVGs generated by SVGMath rendered correctly in SILE.

Sample such SVG, which didn't work for me: https://github.com/akavel/svgmath/blob/master/testdata/test13.out.svg

I tried a doc like below, with current codebase (7f677a1):

\begin{document}
\script[src=packages/svg]

\begin{script}
  local svg = require 'svg'

  local inp = assert(io.open('test13.svg'))
  local data = inp:read '*all'
  inp:close()

  local f = assert(io.opend('foo.tmp', 'w'))
  local fig, w, h = svg.svg_to_ps(data, 72)
  f:write(w, ' ', h, ' ', fig, ' ', data)   -- why doesn't '\n' work here?
  f:close()
\end{script}

Hello SILE! \include-svg-file[src=test13.svg] Included.

\end{document}

Initially, foo.tmp contained 0 0 [...], but after looking into nanosvg.h I noticed it doesn't accept XML namespaces. After sed -i 's/svg://g' test13.svg there was some more interesting stuff in foo.tmp, but still no image in the generated PDF.

Is it because the SVG seems to use mostly <svg:text> elements? Maybe nanosvg ignores them?

[akavel]

(continuing discussion from #220)

Looking at a list of elements described in SVG 1.1 spec vs. what nanosvg supports, there seem indeed to be some seemingly non-stupid missing entries (apart from numerous text-related ones), e.g.: clipPath, marker, mask, symbol & use, ...

[alerque]

I don't think nanosvg is going to serve SILE very well. As mentioned in #446 the support is just too rudimentary for even fairly basic use cases importing a figure.

[akavel]

Ok, got some code which does the parsing of svgmath-generated SVGs in pure Lua, and managed to get prototype rendering done in ZeroBrane Studio with love2d:

(compare with third-party rendering of the SVG at: https://github.com/akavel/svgmath/blob/master/testdata/test13.out.svg)

Not all elements supported yet, but matrices, glyphs and simple lines seem to work ok now.

So, now mostly waiting till someone provides me with a Windows binary of SILE so that I can try:

1. moving/implementing the svg rendering (just enough for svgmath) there,
2. integrating the whole pipeline in SILE.

Though I may have somewhat less time for that over the next 2 weeks.

[simoncozens]

Very interesting! I think long term we are going to want to render SVG to PDF drawing operators ourselves, or use a better library which does that, to keep things in vector format. Doing it ourselves means we can keep the text pipeline going through SILE and leverage the existing fonts/rendering support.

[akavel]

When rendering an equation, how can I output some unicode glyph g at some position dx, dy relative to "current cursor" in the PDF from Lua? I understand that

pdf.add_content('q')

etc. is expected to let me draw curves, but I also need to render some glyphs. I tried using pdf.setstring() but I'm confused as to what can I put in the font argument? I tried some random hacks hoping to make it work:

\begin{document}
Sample inital text

\begin{script}

local pdf = require 'justenoughlibtexpdf'

local buf = 'A'
local font = SILE.font.cache(SILE.font.loadDefaults{}, SILE.shaper.getFace)
local f = pdf.loadfont(font)
if f< 0 then SU.error("Font loading error for "..options) end
font = f
pdf.setstring(100, 100, buf, string.len(buf), font, 0)

\end{script}

Sample final text

\end{document}

but got some assertion fail in dpxutil.c:

This is SILE 0.9.5-unreleased
<../silemath/sample.sil>
[fonts] Looking for Gentium Plus;10;400;;normal;;LTR
[fonts] Resolved font family Gentium Plus -> C:/Windows/Fonts/GentiumPlus-R.ttf
Assertion failed!

Program: C:\dnload\lua-etc\ZeroBraneStudio\bin\lua.exe
File: dpxutil.c, Line 299

Expression: ht && key

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.

Not sure what else I can try...

[akavel]

Ok, got some kind of even more slightly misaligned result by virtue of some unholy abomination of code - but hey, it worked! :D 😄 😂 will need a hell of a cleanup :) and integration work, obviously, for now it's just a one-off prototype of the final element of the pipeline. I cannot upload the code yet as I'm in travel, but here's a teaser screenshot:

[akavel]

Ok, to reduce the bus factor a bit, the code of the prototype is now at: https://github.com/akavel/silemath/blob/master/sample.sil.

• I'd be especially interested to learn if the renderGlyph function can be simplified in some way.
• Also, the <text> nodes in SVGs generated by svgmath have text-anchor="middle", so their horizontal position should be tweaked, but I couldn't yet find out how to do that properly (moving them by -shape[1].width/2 didn't work for me for now, it broke things more than fixed).

[akavel]

Ok, given that I have this sub-problem resolved in principle now, I'm closing this sub-issue and will get back to reporting/discussing in the main #220 issue.