katex-gdef-v8

A Rust library that utilizes KaTeX (v0.16.21) through the V8 engine to render LaTeX math expressions to HTML.

Features

• Fast Processing: Rapid initialization and rendering using V8 snapshots
• Single Instance: Reuse of a single KaTeX instance to minimize loading delays (though not optimized for parallel processing)
• Macro Support: Collect and reuse macros defined with \gdef and similar commands (Note: depends on KaTeX v0.16.21 internal representation)
• Caching Capability: Cache V8 snapshots to the filesystem to reduce startup time
• Font Detection: Analyze rendered HTML to detect which KaTeX fonts are used

Installation

Add this to your Cargo.toml:

[dependencies]
katex-gdef-v8 = "0.1.6"

Usage

Basic Example

use katex_gdef_v8::render;

// KaTeX is initialized automatically on first call
let html = render(r"E = mc^2").unwrap();
println!("{}", html);

Using Options and Macros

use katex_gdef_v8::{render_with_opts, Options, KatexOutput};
use std::collections::BTreeMap;
use std::borrow::Cow;

let mut macros = BTreeMap::new();

// Set custom options
let options = Options {
    display_mode: true,
    output: KatexOutput::HtmlAndMathml,
    error_color: Cow::Borrowed("#ff0000"),
    ..Default::default()
};

// Render first equation (defining macros)
let html1 = render_with_opts(
    r"\gdef\myvar{x} \myvar^2 + \myvar = 0",
    &options,
    &mut macros
).unwrap();
println!("HTML 1: {}", html1);

// Use previously defined macros in second equation
let html2 = render_with_opts(
    r"\myvar^3",
    &options,
    &mut macros
).unwrap();
println!("HTML 2: {}", html2);

Font Detection

The library can analyze rendered KaTeX HTML to determine which fonts are used:

use katex_gdef_v8::{render, font_extract};
use std::collections::HashSet;

// Render a LaTeX expression
let html = render(r"\mathcal{F}(x) = \int_{-\infty}^{\infty} f(x) e^{-2\pi i x \xi} dx").unwrap();

// Extract font information
let used_fonts = font_extract(&html);

// Check if specific fonts are used
println!("Is empty: {}", used_fonts.is_empty());

// Iterate through used fonts
for font_name in used_fonts.clone() {
    // Each font_name is the base name (e.g., "KaTeX_Math-Italic")
    // To get the complete font file name, add file extension:
    println!("Font file: {}.woff2", font_name);
}

// Collect all font names into a HashSet
let font_set: HashSet<&str> = used_fonts.collect();

// Example assertion for testing
assert_eq!(
    font_set,
    HashSet::from([
        "KaTeX_Main-Regular",
        "KaTeX_Math-Italic",
        "KaTeX_Size1-Regular",
        "KaTeX_Caligraphic-Regular"
    ])
);

The FontFlags struct provides detailed information about all KaTeX fonts used in the rendered output, which can be useful for:

• Optimizing font loading by only including required fonts (each font name can be used with extensions like .woff2, .woff, .ttf)
• Selective font preloading in web applications

Setting Up Cache

use katex_gdef_v8::{set_cache, render};
use std::path::Path;

// Set path to cache V8 snapshot
set_cache(Path::new("./katex-cache"));

// Subsequent renderings will be faster
let html = render(r"E = mc^2").unwrap();
println!("{}", html);

Comparison with katex-rs

• Macro collection and reuse: Ability to reuse macros defined in equations in subsequent renderings (main differentiating feature)
• Caching capability: Fast initialization with V8 snapshots
• Single-thread optimization: Shared KaTeX instance in one worker thread (though not suitable for parallel processing)
• Font analysis: Ability to detect which KaTeX fonts are used in the rendered output

Note that katex-rs supports more JavaScript engines (duktape, wasm-js, etc.), making it more versatile in that respect.

License

This project is licensed under the MIT License - see the LICENSE file for details.