# Introduction to gridmicrotex

## What is gridmicrotex?

gridmicrotex renders LaTeX math equations as native R `grid` graphics objects (grobs). It uses the MicroTeX C++ library as its layout engine — MicroTeX parses LaTeX, builds the TeX box model, and computes exact glyph coordinates. The package intercepts this layout data and maps it to native grid primitives (`pathGrob`, `segmentsGrob`, `rectGrob`, `textGrob`), producing a `gTree` that works on any R graphics device at any resolution.

Key features:

- No external LaTeX installation required — MicroTeX is fully embedded
- Resolution-independent vector output on all R devices (PNG, PDF, SVG, …)
- Full math support: fractions, roots, integrals, matrices, Greek letters, accents, delimiters, and more
- Two bundled math fonts: Lete Sans Math (sans-serif, default) and STIX Two Math (serif); additional fonts via `load_font()`
- Color support via `\textcolor{}`
- ggplot2 integration with `geom_latex()` and `element_latex()`
- CJK and multilingual text in `\text{}` blocks

## Basic usage

The core function is `latex_grob()`, which returns a grid grob:

    library(gridmicrotex)
    library(grid)

    g <- latex_grob("\\frac{-b \\pm \\sqrt{b^2 - 4ac}}{2a}", gp = grid::gpar(fontsize = 24))
    grid::grid.newpage()
    grid::grid.draw(g)

For quick rendering, use `grid.latex()`:

    grid::grid.newpage()
    grid.latex("$\\sum_{i=1}^{n} x_i^2$", gp = grid::gpar(fontsize = 28))

## Positioning and justification

Control placement with `x`, `y`, `hjust`, and `vjust`:

    grid::grid.newpage()
    grid.latex("Famous $E = mc^2$", x = 0.1, y = 0.7, hjust = 0, gp = grid::gpar(fontsize = 24))
    grid.latex("F = ma", x = 0.1, y = 0.3, hjust = 0, gp = grid::gpar(fontsize = 24), input_mode = "math")

By default, the input is treated as LaTeX math mode, which treats string as text by default and use `$...$` or `\\(...\\)` delimiters to render math. The `"Famous"` in the first equation above treated as text. The `mixed` mode converts the input to math mode to reduce the user burden for typing `\\text{}` and the conversion might not be perfect, but it should handle most common cases without user intervention. Use `input_mode = "math"` to treat the whole string as math mode (the second example) or if you find a problem with the conversion and render text with `\\text{}`. You can change this with global `latex_options(input_mode = "math")` for heavy math or users who wants to the advantages LaTex macros, etc. The vignette from next example will set the input mode to `math` globally and render the whole string as math mode.

### Aligning to the math baseline

In addition to numeric justifications in `[0, 1]`, `hjust` and `vjust` also accept named values. The most useful one is `vjust = "baseline"`, which places the formula’s math baseline (not the bbox centre) on the anchor point — so a formula sits next to surrounding text the way it would in a typeset document.

    grid::grid.newpage()
    y <- 0.5
    grid::grid.segments(unit(0, "npc"), unit(y, "npc"),
                        unit(1, "npc"), unit(y, "npc"),
                        gp = grid::gpar(col = "grey80"))
    grid::grid.text("if ", x = 0.10, y = y, just = c(0, 0.5),
                    gp = grid::gpar(fontsize = 16))
    grid.latex("$x \\geq \\sqrt{2\\pi}$",
               x = 0.22, y = y,
               hjust = "left", vjust = "baseline",
               gp = grid::gpar(fontsize = 16))
    grid::grid.text(", then proceed.", x = 0.62, y = y, just = c(0, 0.5),
                    gp = grid::gpar(fontsize = 16))

`hjust` accepts `"left"`/`"bbleft"`, `"center"`/`"centre"`/`"middle"`/ `"bbcentre"`, and `"right"`/`"bbright"`. `vjust` accepts `"bottom"`, `"center"`/`"centre"`/`"middle"`, `"top"`, and `"baseline"`.

### Named anchors with `\mark{}`

The `\mark{name}` macro records a named anchor at its position inside the formula. `grobMark()` then resolves the anchor to a pair of grid units, ready to drive an arrow, callout, or any other grob.

A mark works at any nesting level — between top-level tokens, on a compound sub-expression like `b^2`, even inside a superscript or fraction. The position inherits the surrounding transform (font shrink for scripts, scaling, rotation), so the anchor lands on the rendered glyph rather than a pre-layout offset.

    g <- latex_grob(
      r"($a^2 + b\mark{term}^2 \mark{equals}= c^2$)",
      x = 0.5, y = 0.4,
      gp = grid::gpar(fontsize = 28)
    )
    grid::grid.newpage()
    grid::grid.draw(g)

    # Callout 1: the "=" sign, pointed at from above.
    mk_eq <- grobMark(g, "equals")
    grid::grid.segments(mk_eq$x, mk_eq$y + unit(15, "mm"),
                        mk_eq$x, mk_eq$y + unit(3, "mm"),
                        arrow = grid::arrow(length = unit(2, "mm"), type = "closed"),
                        gp = grid::gpar(col = "red"))
    grid::grid.text("equals", x = mk_eq$x, y = mk_eq$y + unit(18, "mm"),
                    gp = grid::gpar(col = "red", fontsize = 11))

    # Callout 2: the b^2 term, pointed at from below — the mark sits at the
    # end of the term, including the superscript's smaller scale.
    mk_bsq <- grobMark(g, "term")
    grid::grid.segments(mk_bsq$x - unit(6, "mm"), mk_bsq$y - unit(15, "mm"),
                        mk_bsq$x - unit(2, "mm"), mk_bsq$y - unit(3, "mm"),
                        arrow = grid::arrow(length = unit(2, "mm"), type = "closed"),
                        gp = grid::gpar(col = "blue"))
    grid::grid.text("b² term",
                    x = mk_bsq$x - unit(7, "mm"),
                    y = mk_bsq$y - unit(18, "mm"),
                    just = "right",
                    gp = grid::gpar(col = "blue", fontsize = 11))

Because the returned units carry the grob’s viewport position and `hjust`/`vjust`, you can pass them straight to `grid.points`, `grid.segments`, or any other grid drawing function — no manual offset arithmetic.

`\mark` records a single point, not a span. To centre a callout over a multi-glyph term, place the mark at the term’s end and shift in your drawing code, or place a pair of marks (`\mark{l}…\mark{r}`) and use their midpoint.

## Colors

You can use `r"()"` raw strings to write LaTeX with regular newlines and quotes without escaping. Set the formula color via `gp`, or use `\textcolor{}` within the LaTeX:

    latex_options(input_mode = "math") # Set math mode globally
    grid::grid.newpage()
    grid.latex(
      r"(\textcolor{red}{\alpha} + \textcolor{blue}{\beta} = \gamma)",
      gp = grid::gpar(fontsize = 28)
    )

## Math fonts

The package ships with two math fonts, both loaded automatically:

Alias | Font | License
--- | --- | ---
`"lete"` (default) | Lete Sans Math | SIL Open Font License
`"stix"` | STIX Two Math | SIL Open Font License

    available_math_fonts()
    #> [1] "Lete Sans Math" "STIX Two Math"

    latex_options(math_font = "stix")
    grid::grid.newpage()
    grid.latex(r"(\int_0^1 f(x)\,dx)", gp = grid::gpar(fontsize = 24))

    # Switch back to the default (Lete Sans Math)
    latex_options(math_font = "lete")

You can also override the font per call via `math_font`:

    grid::grid.newpage()
    grid::pushViewport(grid::viewport(layout = grid::grid.layout(2, 1)))
    grid::pushViewport(grid::viewport(layout.pos.row = 1))
    grid.latex(r"(\int_0^1 f(x)\,dx)", gp = grid::gpar(fontsize = 24))
    grid::upViewport()
    grid::pushViewport(grid::viewport(layout.pos.row = 2))
    grid.latex(r"(\int_0^1 f(x)\,dx)", gp = grid::gpar(fontsize = 24), math_font = "stix")
    grid::upViewport(2)

Use `available_math_fonts()` to list loaded fonts and `check_fonts()` for a diagnostic report.

### Advanced: loading custom fonts

Use `load_font()` to add any additional OpenType math font. The OpenType MATH table is parsed directly in C++ — no companion metrics file or external toolchain is required:

    load_font("path/to/MyFont.otf")

### Render modes

gridmicrotex supports two rendering modes for math glyphs:

- `"typeface"` (default): Renders glyphs as native text using the math font’s typeface. This produces selectable, searchable, and accessible text in PDF and SVG output. Bundled math fonts (Lete Sans Math, STIX Two Math) and any registered via `load_font()` are read directly from their OTF files — no system-wide font install is required. Requires a device that supports the R 4.3 glyph engine (e.g., `ragg::agg_png()`, `svglite::svglite()`, `grDevices::cairo_pdf()`). On devices that do not (e.g., the base `pdf()` device), the package automatically falls back to path mode with a warning.

- `"path"`: Renders each glyph as a filled vector path. This works on all R graphics devices and produces pixel-perfect output. However, text in PDF/SVG output is not selectable or searchable.

    # Default typeface mode (selectable text in PDF/SVG)
    grid.latex("E = mc^2", gp = grid::gpar(fontsize = 24))

    # Explicit path mode (works everywhere, but text is not selectable)
    grid.latex("E = mc^2", gp = grid::gpar(fontsize = 24), render_mode = "path")

> Important: Do not use `showtext::showtext_auto()` with typeface mode. The showtext package globally intercepts all text rendering and converts it to vector paths. This silently defeats typeface mode, causing all math glyphs to appear as paths instead of native text — even on devices like `svglite` and `ragg` that fully support font embedding. If you need showtext for other parts of your plot, disable it before drawing LaTeX formulas:

>     showtext::showtext_auto(FALSE)
>     grid.latex("E = mc^2", gp = grid::gpar(fontsize = 24))  # typeface mode works correctly

## Querying dimensions

`latex_dims()` returns the bounding box of an expression:

    dims <- latex_dims("\\frac{a}{b}", gp = grid::gpar(fontsize = 20))
    dims
    #> $width
    #> [1] 7bigpts
    #>
    #> $height
    #> [1] 25bigpts
    #>
    #> $depth
    #> [1] 9bigpts
    #>
    #> $baseline
    #> [1] 9.36317294836044bigpts
    #>
    #> $is_split
    #> [1] FALSE

This is useful for layout calculations and ensuring labels fit.

## Text rendering and CJK support

Text inside `\text{}` and `\mbox{}` is rendered using R’s standard text-rendering system. This means `gp$fontfamily` controls the font for all text content — Latin letters, CJK characters, Cyrillic, and any other script your R graphics device supports:

    grid::grid.newpage()
    grid.latex("x^2 + \\text{你好}", gp = grid::gpar(fontsize = 24, fontfamily = "sans"))

Any font available to R works: base families like `"sans"`, `"serif"`, `"mono"`, or fonts registered via showtext / systemfonts.

### Font pairing

The bundled math fonts have different styles. For a consistent look, pair them with a matching `fontfamily`:

Math font | Style | Suggested `fontfamily`
--- | --- | ---
Lete Sans Math (`"lete"`, default) | Sans-serif | `"sans"`
STIX Two Math (`"stix"`) | Serif | `"serif"`

    grid::grid.newpage()
    grid.latex(
      "\\text{Theorem: } \\forall x \\in \\mathbb{R},\\; x^2 \\geq 0",
      math_font = "stix",
      gp = grid::gpar(fontfamily = "serif", fontsize = 12)
    )

## Supported LaTeX

gridmicrotex uses the MicroTeX engine, which is a math formula renderer, not a full document typesetter. It covers the vast majority of math notation you would use in plots and figures, but does not attempt to replace a full LaTeX installation.

### Complicated examples

    grid::grid.newpage()
    grid.latex(paste0(
          "\\begin{array}{l}",
          "  \\forall\\varepsilon\\in\\mathbb{R}_+^*\\ \\exists\\eta>0",
          "\\ |x-x_0|\\leq\\eta\\Longrightarrow|f(x)-f(x_0)|\\leq\\varepsilon\\\\",
          "  \\det",
          "  \\begin{bmatrix}",
          "      a_{11}&a_{12}&\\cdots&a_{1n}\\\\",
          "      a_{21}&\\ddots&&\\vdots\\\\",
          "      \\vdots&&\\ddots&\\vdots\\\\",
          "      a_{n1}&\\cdots&\\cdots&a_{nn}",
          "  \\end{bmatrix}",
          "  \\overset{\\mathrm{def}}{=}\\sum_{\\sigma\\in\\mathfrak{S}_n}",
          "\\varepsilon(\\sigma)\\prod_{k=1}^n a_{k\\sigma(k)}\\\\",
          "  \\int_0^\\infty{x^{2n} e^{-a x^2}\\,dx} = \\frac{2n-1}{2a}",
          " \\int_0^\\infty{x^{2(n-1)} e^{-a x^2}\\,dx}",
          " = \\frac{(2n-1)!!}{2^{n+1}} \\sqrt{\\frac{\\pi}{a^{2n+1}}}\\\\",
          "\\end{array}"
    ), gp = grid::gpar(fontsize = 16))

    grid::grid.newpage()

    grid.latex(
      "
      \\newcolumntype{s}{>{\\color{#1234B6}}c}
    \\begin{array}{|c|c|c|s|}
      \\hline
      \\rowcolor{Tan}\\multicolumn{4}{|c|}{\\textcolor{white}{\\bold{\\text{Table Head}}}}\\\\
      \\hline
      \\text{Matrix}&\\multicolumn{2}{|c|}{\\text{Multicolumns}}&\\text{Font size commands}\\\\
      \\hline
      \\begin{pmatrix}
          \\alpha_{11}&\\cdots&\\alpha_{1n}\\\\
          \\hdotsfor{3}\\\\
          \\alpha_{n1}&\\cdots&\\alpha_{nn}
      \\end{pmatrix}
      &\\large \\text{Left}&\\cellcolor{#00bde5}\\small \\textcolor{white}{\\text{\\bold{Right}}}
      &\\small \\text{small Small}\\\\
      \\hline
      \\multicolumn{4}{|c|}{\\text{Table Foot}}\\\\
      \\hline
    \\end{array}
      ",
      gp = grid::gpar(fontsize = 22)
    )

    grid::grid.newpage()
    grid.latex(
      "\\definecolor{gris}{gray}{0.9}
    \\definecolor{noir}{rgb}{0,0,0}
    \\definecolor{bleu}{rgb}{0,0,1}
    \\fatalIfCmdConflict{false}
    \\newcommand{\\pa}{\\left|}
    \\begin{array}{c}
      \\LaTeX\\\\
      \\begin{split}
          |I_2| &= \\pa\\int_0^T\\psi(t)\\left\\{ u(a,t)-\\int_{\\gamma(t)}^a \\frac{d\\theta}{k} (\\theta,t) \\int_a^\\theta c(\\xi)
              u_t (\\xi,t)\\,d\\xi\\right\\}dt\\right|\\\\
          &\\le C_6 \\Bigg|\\pa f \\int_\\Omega \\pa\\widetilde{S}^{-1,0}_{a,-}
              W_2(\\Omega, \\Gamma_1)\\right|\\ \\right|\\left| |u|\\overset{\\circ}{\\to} W_2^{\\widetilde{A}}(\\Omega\\Gamma_r,T)\\right|\\Bigg|\\\\
          &\\\\
          &\\begin{pmatrix}
              \\alpha&\\beta&\\gamma&\\delta\\\\
              \\aleph&\\beth&\\gimel&\\daleth\\\\
              \\mathfrak{A}&\\mathfrak{B}&\\mathfrak{C}&\\mathfrak{D}\\\\
              \\boldsymbol{\\mathfrak{a}}&\\boldsymbol{\\mathfrak{b}}&\\boldsymbol{\\mathfrak{c}}&\\boldsymbol{\\mathfrak{d}}
          \\end{pmatrix}
          \\quad{(a+b)}^{\\frac{n}{2}}=\\sqrt{\\sum_{k=0}^n\\tbinom{n}{k}a^kb^{n-k}}\\quad
              \\Biggl(\\biggl(\\Bigl(\\bigl(()\\bigr)\\Bigr)\\biggr)\\Biggr)\\\\
          &\\forall\\varepsilon\\in\\mathbb{R}_+^*\\ \\exists\\eta>0\\ |x-x_0|\\leq\\eta\\Longrightarrow|f(x)-f(x_0)|\\leq\\varepsilon\\\\
          &\\det
          \\begin{bmatrix}
              a_{11}&a_{12}&\\cdots&a_{1n}\\\\
              a_{21}&\\ddots&&\\vdots\\\\
              \\vdots&&\\ddots&\\vdots\\\\
              a_{n1}&\\cdots&\\cdots&a_{nn}
          \\end{bmatrix}
          \\overset{\\mathrm{def}}{=}\\sum_{\\sigma\\in\\mathfrak{S}_n}\\varepsilon(\\sigma)\\prod_{k=1}^n a_{k\\sigma(k)}\\\\
          &\\Delta f(x,y)=\\frac{\\partial^2f}{\\partial x^2}+\\frac{\\partial^2f}{\\partial y^2}\\qquad\\qquad \\fcolorbox{noir}{gris}
              {n!\\underset{n\\rightarrow+\\infty}{\\sim} {\\left(\\frac{n}{e}\\right)}^n\\sqrt{2\\pi n}}\\\\
          &\\sideset{_\\alpha^\\beta}{_\\gamma^\\delta}{
          \\begin{pmatrix}
              a&b\\\\
              c&d
          \\end{pmatrix}}
          \\xrightarrow[T]{n\\pm i-j}\\sideset{^t}{}A\\xleftarrow{\\overrightarrow{u}\\wedge\\overrightarrow{v}}
              \\underleftrightarrow{\\iint_{\\mathds{R}^2}e^{-\\left(x^2+y^2\\right)}\\,\\mathrm{d}x\\mathrm{d}y}
      \\end{split}\\\\
      \\rotatebox{30}{\\sum_{n=1}^{+\\infty}}\\quad\\mbox{Mirror rorriM}\\reflectbox{\\mbox{Mirror rorriM}}
    \\end{array}",
      gp = grid::gpar(fontsize = 22),
      render_mode = "path"
    )

### What is not supported

MicroTeX is a math formula renderer, not a full LaTeX engine. The following are outside its scope:

- Document structure: `\section`, `\begin{document}`, page layout, headers/footers, `\tableofcontents`
- Package loading: `\usepackage{}` — all supported commands are built in
- Paragraph text: line breaking, hyphenation, justified paragraphs
- TikZ / PGF drawing commands
- Images: `\includegraphics`
- Cross-references: `\label`, `\ref`, `\cite`, bibliographies
- Theorem environments: `\begin{theorem}`, `\begin{proof}`
- Lists: `itemize`, `enumerate`, `description`
- Some amsmath commands: `\substack`, `\tag`, equation numbering

For most statistical graphics use cases — axis labels, annotations, legends, and in-plot formulas — the supported feature set is more than sufficient.

## Project-wide defaults

`latex_options()` sets defaults for `math_font` and `render_mode`, used by `latex_grob()`, `grid.latex()`, `latex_dims()`, and `latex_tree()` whenever the corresponding argument is not supplied at the call site. Size is controlled at the grob level via `gp$fontsize` / `gp$lineheight` (see Basic usage).

    latex_options(math_font = "stix", render_mode = "typeface")

    # Later calls pick these up automatically
    grid.latex("\\sum_{i=1}^{n} i^{2}", gp = grid::gpar(fontsize = 14))

    # Query current settings
    latex_options()

    # Reset to built-in defaults
    reset_latex_options()

Explicit arguments always win. Setting `math_font` via `latex_options()` also updates the MicroTeX engine default, so you don’t also need a separate font-setup call.

## User-defined macros

`define_macro()` registers zero-argument shorthands that are expanded by text substitution before the expression reaches MicroTeX. Handy for recurring notation:

    define_macro("RR", "\\mathbb{R}")
    define_macro("eps", "\\varepsilon")

    grid::grid.newpage()
    grid.latex("\\forall \\eps > 0, \\eps \\in \\RR", gp = grid::gpar(fontsize = 24))

    clear_macros()

Macro names must be ASCII letters. Expansion iterates to a fixed point, so macros can reference other macros. Use `list_macros()` to see currently registered ones, and `clear_macros()` (with no arguments) to drop them all.

For parameterised macros (0–9 arguments) scoped to a single expression, MicroTeX also accepts plain-TeX `\def`:

    grid::grid.newpage()
    grid.latex(
      r"(\def\norm#1{\left\lVert #1 \right\rVert}
          \def\inner#1#2{\langle #1, #2 \rangle}
          \norm{\vec{v}} = \sqrt{\inner{\vec{v}}{\vec{v}}})",
      gp = grid::gpar(fontsize = 24)
    )

`\def` definitions live only for the duration of the expression they appear in, so they are the right tool for a parameterised abbreviation local to one label. Reach for `define_macro()` instead when you want a shorthand to persist across many plots in the same R session.

## Layout caching

Parsed layouts are memoised by `(tex, fontsize, math_font, render_mode, ...)`. Re-drawing the same formula — for example, the same axis label across many plots — reuses the cached layout:

    latex_cache_info()       # size / max_size / hits / misses
    latex_cache_limit(1024)  # raise or lower the LRU capacity
    latex_cache_clear()      # wipe the cache (e.g. after re-loading fonts)

Set the limit to `0` to disable caching entirely.

## Introspecting a formula

`latex_tree()` returns the raw draw-record table plus bbox metadata, useful for debugging alignment, counting glyphs, or building custom grobs on top of the layout:

    tr <- latex_tree("\\frac{a}{b}")
    tr
    #> <latex_tree>
    #>   tex:         \frac{a}{b}
    #>   render_mode: typeface
    #>   bbox:        width=7.00  height=25.00  depth=9.00  baseline=0.63 (bigpts)
    #>   records:     3
    #>     glyph      2
    #>     line       1
    head(tr$records, 3)
    #>    type         x      y glyph font_size   color    x2     y2 width height rx
    #> 1 glyph 0.1890002  7.196  3628        14 #000000    NA     NA    NA     NA NA
    #> 2  line 0.0000000 10.596    NA        NA #000000 7.392 10.596    NA     NA NA
    #> 3 glyph 0.0000000 25.796  3629        14 #000000    NA     NA    NA     NA NA
    #>   ry  lwd text font_style rotation path codepoint
    #> 1 NA   NA <NA>         NA        0 NULL        NA
    #> 2 NA 1.32 <NA>         NA        0 NULL        NA
    #> 3 NA   NA <NA>         NA        0 NULL        NA
    #>                                                                                           font_file
    #> 1 C:/Users/alim/AppData/Local/Temp/RtmpwxPy6k/Rinst53ac7f1d7fb6/gridmicrotex/fonts/LeteSansMath.otf
    #> 2                                                                                              <NA>
    #> 3 C:/Users/alim/AppData/Local/Temp/RtmpwxPy6k/Rinst53ac7f1d7fb6/gridmicrotex/fonts/LeteSansMath.otf

## Debug overlay

Pass `debug = TRUE` to `latex_grob()` / `grid.latex()` to overlay diagnostics on the rendered formula — the full bounding box (dashed gray), the baseline (solid red), and a dot at each draw record’s origin. Useful for checking vertical alignment between a formula and surrounding grobs:

    grid::grid.newpage()
    grid.latex("x^{2} + y_{i}", gp = grid::gpar(fontsize = 30), debug = TRUE)

## Comparison with alternatives

Approach | LaTeX required? | Device independent? | Vector? | Math coverage
--- | --- | --- | --- | ---
`tikzDevice` | Yes | No | Yes | Full
`xdvir` | Yes | No | Yes | Full
`latexpdf` | Yes | No | Yes | Full (tables)
`latex2exp` | No | Yes | Yes | Limited
`plotmath` | No | Yes | Yes | Limited
gridmicrotex | No | Yes | Yes | Broad

## Graphics backend

The default graphics device on Windows (`windows()`) and macOS (`quartz()`) may not find the bundled math fonts, producing warnings like:

    font family not found in Windows font database

To avoid this, switch to a modern graphics backend that uses systemfonts for font resolution:

    # For knitr / R Markdown --- add to your setup chunk:
    knitr::opts_chunk$set(dev = "ragg_png")

    # For interactive use:
    options(device = function(...) ragg::agg_png(tempfile(fileext = ".png"), ...))

Recommended backends:

Backend | Format | Package
--- | --- | ---
`ragg::agg_png()` | PNG | ragg
`svglite::svglite()` | SVG | svglite
`grDevices::cairo_pdf()` | PDF | Base R (Cairo build)

Alternatively, use `render_mode = "path"` to bypass font lookup entirely — glyphs are drawn as vector paths, which works on all devices but produces non-selectable text in PDF/SVG.