KMPCharts/chart-realtime

chart-realtime

KMP real-time line chart for Android. Renders multiple sensor signals at 200Hz+ without frame drops.

Features

• Multiple signals on one chart, added/removed dynamically
• FIFO circular buffer — lock-free writes at 200Hz+, safe render reads at 60fps
• Level-of-Detail decimation — renders O(pixels) regardless of buffer size (1h+ of data)
• Dirty-flag render: skips GPU draw when no new data since last frame
• Configurable render rate: default 30 fps, override via targetFps (pass null for max display Hz)
• X axis: scrolling window, seconds from configurable t0
• Y axis: auto-fit or fixed range
• Material3 default theme, fully customizable via ChartTheme

Installation

// settings.gradle.kts
include(":chart-realtime")

Or Maven local:

./gradlew :chart-realtime:publishToMavenLocal

// build.gradle.kts
implementation("dev.dtrentin:chart-realtime:0.5.0-SNAPSHOT")

Quick start (3 lines)

val state = remember { RealtimeChartState(ChartConfig()) }
LaunchedEffect(state) {
    state.addSignal("ecg", SignalConfig(color = Color.Green))
    sensorFlow.collect { v -> state.push("ecg", System.currentTimeMillis(), v) }
}
RealtimeChart(state = state, modifier = Modifier.fillMaxSize())

Configuration

ChartConfig(
    xWindowSeconds   = 10f,                    // visible window width
    yRange           = YRange.Auto(),           // or YRange.Fixed(-1f, 1f)
    t0               = T0.FirstSample,          // or T0.Fixed(epochMs)
    targetFps        = 30,                      // default 30 fps; null = max display refresh rate
    theme            = ChartTheme(              // optional visual override
        backgroundColor = Color(0xFF1A1A2E),
        gridColor       = Color(0x22FFFFFF),
        axisColor       = Color(0xFFBBBBBB),
    ),
)

Level of Detail

ChartConfig(lodMode = LodMode.MIN_MAX)  // default — zero-alloc, preserves peaks
ChartConfig(lodMode = LodMode.LTTB)     // visually smooth, slight alloc per frame

Axis Labels

ChartConfig(
    xLabelMode = AxisLabelMode.INSIDE,   // default — labels over chart area
    yLabelMode = AxisLabelMode.BESIDE,   // reserved margin for Y labels
)
// AxisLabelMode.HIDDEN — hides labels on that axis

Material3 Theme

val theme = rememberMaterialChartTheme()
RealtimeChart(state = state, theme = theme)

Flow API

// From Flow<Float> (auto-timestamp)
state.collectFrom("accel_x", accelerometerFlow, viewModelScope)

// From Flow<Pair<Long, Float>> (explicit timestamp)
state.collectFrom("ecg", ecgFlow, viewModelScope)  // ecgFlow emits (timestampMs, value)

Performance notes

• Data thread pushes at any rate; render thread reads at targetFps (default 30) or display refresh if null
• TieredBuffer keeps ~1h history per signal (3-tier ring, no caller config)
• LoD decimation reduces >pixel-count data to min/max per pixel column
• Pre-allocated arrays — zero GC on hot render path (except LoD scratch, see TODO in LodDecimator.kt)
• Dirty-flag skips canvas draw when buffer unchanged since last frame

Requirements

• Android minSdk 26
• Jetpack Compose / Compose Multiplatform 1.8+
• Kotlin 2.1+

License

MIT License — see LICENSE.