src/com.mocharealm.accompanist.lyrics.text/NativeTextEngine

NativeTextEngine

actual class NativeTextEngine

expect class NativeTextEngine

Native text engine for SDF glyph generation and text layout.

This engine uses Rust for high-performance text shaping (via rustybuzz) and SDF generation. It maintains a glyph atlas with LRU cache eviction.

Usage

val engine = NativeTextEngine()
engine.init(2048, 2048)  // Initialize with atlas size
engine.loadFont(fontBytes)  // Load primary font

// Process text and get layout
val layoutJson = engine.processText("Hello", 48f, 400f)

// Upload pending glyphs to atlas
if (engine.hasPendingUploads()) {
    val uploads = parsePendingUploads(engine.getPendingUploads())
    atlasManager.updateAtlas(uploads)
}

SDF Processing

Glyph data is pre-processed in Rust with alpha values:

A channel: normal text alpha (smoothstep at threshold 0.7)
G channel: shadow alpha (smoothstep falloff for glow effect)

actual class NativeTextEngine

Constructors

NativeTextEngine

constructor()

expect constructor()

constructor()

Types

Companion

object Companion

object Companion

Functions

clearFallbackFonts

actual external fun clearFallbackFonts()

expect fun clearFallbackFonts()

Clears all loaded fallback fonts.

actual external fun clearFallbackFonts()

actual external fun destroy()

expect fun destroy()

Releases all resources and clears the glyph cache.

actual external fun destroy()

actual external fun getAtlasSize(): String

expect fun getAtlasSize(): String

Gets the current atlas size.

actual external fun getAtlasSize(): String

getPendingUploads

actual external fun getPendingUploads(): String

expect fun getPendingUploads(): String

Gets pending glyph uploads as JSON. Each upload contains position, size, and RGBA pixel data (pre-processed SDF).

actual external fun getPendingUploads(): String

getPendingUploadsDirect

external fun getPendingUploadsDirect(buffer: ByteBuffer): Int

external fun getPendingUploadsDirect(buffer: ByteBuffer): Int

hasPendingUploads

actual external fun hasPendingUploads(): Boolean

expect fun hasPendingUploads(): Boolean

Checks if there are pending glyph uploads.

actual external fun hasPendingUploads(): Boolean

actual external fun init(atlasWidth: Int, atlasHeight: Int)

expect fun init(atlasWidth: Int, atlasHeight: Int)

Initializes the text engine with the given atlas dimensions. Must be called before any other operations.

actual external fun init(atlasWidth: Int, atlasHeight: Int)

loadFallbackFont

actual external fun loadFallbackFont(bytes: ByteArray)

expect fun loadFallbackFont(bytes: ByteArray)

Loads a fallback font for missing glyphs. Fallback fonts are tried in order when the primary font doesn't contain a glyph.

actual external fun loadFallbackFont(bytes: ByteArray)

loadFallbackFontFd

external fun loadFallbackFontFd(fd: Int): Boolean

loadFallbackFontFromAsset

fun NativeTextEngine.loadFallbackFontFromAsset(context: Context, assetPath: String): Boolean

Loads a fallback font from Android assets using zero-copy file descriptor. More memory efficient than loading entire font into ByteArray.

loadFallbackFontFromFile

fun NativeTextEngine.loadFallbackFontFromFile(filePath: String): Boolean

Loads a fallback font from a file path using zero-copy file descriptor.

actual external fun loadFont(bytes: ByteArray)

expect fun loadFont(bytes: ByteArray)

Loads the primary font for text rendering.

actual external fun loadFont(bytes: ByteArray)

actual external fun processText(text: String, sizeFn: Float, weight: Float): String

expect fun processText(text: String, sizeFn: Float, weight: Float = 400.0f): String

Processes text and returns layout information as JSON. This also generates SDF glyphs for any new characters.

actual external fun processText(text: String, sizeFn: Float, weight: Float): String

processTextDirect

external fun processTextDirect(text: String, sizePx: Float, weight: Float, buffer: ByteBuffer): Int

external fun processTextDirect(text: String, sizePx: Float, weight: Float, buffer: ByteBuffer): Int