RaTeX

Native LaTeX math on Android (Kotlin + Canvas). AAR includes KaTeX fonts. minSdk 21, targetSdk 34.

Out of the box

1. Add dependency — In your app's build.gradle:

   implementation("io.github.erweixin:ratex-android:0.1.14")
   

2. Use — Add RaTeXView in your layout and set LaTeX in code; fonts load automatically on first render.

   binding.mathView.latex = """\frac{-b \pm \sqrt{b^2-4ac}}{2a}"""
   binding.mathView.fontSize = 24f   // dp — no manual density conversion needed
   

   Optional: To preload fonts at startup, call RaTeXFontLoader.loadFromAssets(context, "fonts") in your Application or first screen.

Local development (building from source)

Prerequisites: NDK 26+, Rust + cargo install cargo-ndk, and targets:

rustup target add aarch64-linux-android armv7-linux-androideabi x86_64-linux-android

Build from repo root:

bash platforms/android/build-android.sh
# → src/main/jniLibs/{arm64-v8a,armeabi-v7a,x86_64}/libratex_ffi.so

Include as a local module in settings.gradle:

include(":ratex-android")
project(":ratex-android").projectDir = file("path/to/RaTeX/platforms/android")

Then in your app: implementation(project(":ratex-android")).

Usage

Block formula — RaTeXView

<io.ratex.RaTeXView android:id="@+id/mathView"
    android:layout_width="wrap_content" android:layout_height="wrap_content" />

binding.mathView.latex       = """\frac{-b \pm \sqrt{b^2-4ac}}{2a}"""
binding.mathView.fontSize    = 24f     // dp — no manual density conversion needed
binding.mathView.displayMode = true    // true = display/block (default); false = inline/text
binding.mathView.color       = android.graphics.Color.parseColor("#1E88E5")

Inline formula — RaTeXSpan

RaTeXSpan is a ReplacementSpan that renders a LaTeX formula inline with surrounding text, baseline-aligned, with line height expanding automatically.

Rendering is async. Call RaTeXSpan.create from a coroutine:

private val scope = CoroutineScope(Dispatchers.Main + SupervisorJob())

fun showInlineFormula(textView: TextView) {
    scope.launch {
        val span = RaTeXSpan.create(
            context  = this@MainActivity,
            latex    = """\frac{1+\sqrt{5}}{2}""",
            fontSize = 18f   // dp
        )
        val ssb = SpannableStringBuilder("黄金比例 φ = ")
        val start = ssb.length
        ssb.append("\u200B")
        ssb.setSpan(span, start, ssb.length, 0)
        ssb.append(" ≈ 1.618")
        textView.text = ssb
    }
}

Parameter	Type	Description
context	Context	Used for asset access during font loading.
latex	String	LaTeX math-mode string (no surrounding $ or \[…\]).
fontSize	Float	Font size in dp. Converted to px internally.

Throws RaTeXException if the formula cannot be parsed.

Low-level (Compose / custom drawing)

import android.graphics.Color

// display mode (default)
val dl = RaTeXEngine.parse(latex)
// inline mode
val dl = RaTeXEngine.parse(latex, displayMode = false)
// custom default color
val blueDl = RaTeXEngine.parse(latex, color = Color.parseColor("#1E88E5"))

val renderer = RaTeXRenderer(dl, fontSize) { RaTeXFontLoader.getTypeface(it) }
renderer.draw(canvas)

Explicit LaTeX colors such as \color{...} still take precedence over the default color.

Demo

From repo root: bash platforms/android/build-android.sh, then open demo/android in Android Studio and run.

Troubleshooting: UnsatisfiedLinkError → run build-android.sh. NDK not found → install NDK 26+ or set ANDROID_NDK_HOME.

Publishing (maintainers)

• Local: ./gradlew :ratex-android:publishReleasePublicationToMavenLocal
• Maven Central: configure central.sonatype.com + GPG, set SONATYPE_NEXUS_USERNAME / SONATYPE_NEXUS_PASSWORD / GPG_PRIVATE_KEY / GPG_PASSPHRASE in gradle.properties.
• CI: push tag v{VERSION} → .github/workflows/release-android.yml publishes to Central automatically.