1e7c0c1e45425108758df616a87d4f975fcd8070 — Sebastien Binet 2 years ago e3c6a19
2021/2021-02-16-gioui-latex: first import
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# 2021-02-16-gioui-latex

`go-present` link: [slides](https://talks.godoc.org/github.com/sbinet/talks/2021/2021-02-16-gioui-latex/talk.slide)

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Drawing LaTeX equations with Gio
Gio February Community Call, 2021-02-16

Sebastien Binet

* Gio and me

It all started with these 2 "simple" use cases:

- Seb, I'd like to be able to render LaTeX equations into my [[https://pkg.go.dev/go-hep.org/x/hep@v0.28.4/hplot?readme=expanded#section-readme][hplot]] plots (_ie:_ `$\frac{\sqrt{1+x}}{2\pi}$`)

- Seb, it would be great to have an interactive playground to show some physics features, such as a solar system simulation that exercises basic Newtonian mechanics



Ok, this just has to do with drawing things in 2-D...
How do you do that?

* How to draw LaTeX equations

* How to draw LaTeX equations

At a low level, this is essentially the same than what we did previously with Gio: drawing an equation with a squared root is just like stroking a path.

.image _figs/sqrt.png 100 _

Symbols, letters, ..., well, glyphs of a font's package are actually described in the TTF/OTF format as segments (lines, Bézier curves, circles, etc...).

So once a LaTeX equation has been properly parsed, displaying it (or any piece of text, really) can be seen as just drawing paths.

* How to display text

.image _figs/glyphterms_2x.png 550 _

* github.com/go-latex/latex

- `mtex`: parse a `LaTeX` equation, produce an AST of `tex.Node`

  package mtex // import "github.com/go-latex/latex/mtex"
  // Parse parses a LaTeX math expression and returns the TeX-like box model and
  // an error if any.
  func Parse(expr string, fontSize, DPI float64, backend font.Backend) (tex.Node, error)

- `tex`: analyze an AST and applies the `TeX` formulae for typesetting (boxes, alignment, etc...)
- `mtex`: render an AST to a `drawtex.Canvas`

  func Render(dst Renderer, expr string, size, dpi float64, fonts *ttf.Fonts) error
- `drawtex/drawimg`: render an AST as an `image.Image`
- `drawtex/drawpdf`: render an AST as a PDF document
- `cmd/mtex-render`: render a LaTeX equation to a `drawtex.Canvas` or to Gio.

* mtex-render + Liberation fonts

.image _figs/go-latex-liberation.png _ 600

* mtex-render + Latin-Modern fonts

.image _figs/go-latex-lm.png _ 600

* mtex-render

As can be seen, it's still a work in progress :)

`go-latex` uses the same algorithm than what is done in [[https://matplotlib.org][matplotlib]], to have the look and feel of LaTeX without having to shell out to `latex` (which can be rather slow, and needs a complete LaTeX environment).

.link https://github.com/go-latex/latex
.link https://matplotlib.org/3.2.1/tutorials/text/mathtext.html

* star-tex

* star-tex: a TeX engine in Go

Implementing the `TeX` parser and its mathematical equation parser was fun but:

- it's not a complete TeX engine
- it has numerous (parsing) bugs
- it implements "by hand" a subset of the "real" LaTeX math equation language

_"Solution":_ implement a real TeX engine in Go.

.link https://sr.ht/~sbinet/star-tex

The aim is to have a complete, pure-Go, `tex-live` compatible TeX engine.


 $> star-tex ./testdata/hello.tex o.dvi
 $> dvipdf o.dvi
 $> pdf o.pdf

.image _figs/star-tex.png