Ink App Builder

Android (Google)OfficialCreated by Google LLCDistributed by Android (Google)

Skill
Tool integration
Software development
Apache-2.0
No issues found

From the author

Adds inking and freehand drawing capabilities to an Android app using Jetpack Ink (androidx.ink) and Compose. Use this skill when implementing stylus or touch drawing surfaces, rendering wet and dry ink strokes, configuring stock brushes (pressure pen, marker, highlighter), implementing geometry-based erasing, linear undo and redo history, or stroke persistence with Room. Delivers working Compose and ViewModel implementations. Don't use for View-based (XML) inking or programmatic custom BrushFamily creation. For custom BrushFamily creation, custom tip shapes, or behavior node graphs, suggest the ink-custom-brush-builder skill.

— the description by Google LLC

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

The ink-app-builder skill provides a structured approach to implementing freehand drawing in Android applications using the androidx.ink library and Jetpack Compose. It focuses on the two-phase rendering model, utilizing InProgressStrokes for real-time wet ink capture and CanvasStrokeRenderer for displaying finalized dry ink strokes. The skill covers dependency configuration, brush management, geometry-based erasing, and stroke persistence using Room, ensuring a flicker-free drawing experience through synchronous state management.

What it does

Configures Jetpack Ink dependencies and build settings for Android projects.
Implements a dual-layer drawing surface using Compose Canvas and InProgressStrokes.
Provides patterns for managing stock brushes like pressure pens, markers, and highlighters.
Enables geometry-based stroke erasing and linear undo/redo history.
Supports stroke persistence and retrieval using Room and Kotlin serialization.
Delivers ViewModel and Compose implementations for state management.

When to use it

When adding freehand drawing or stylus input to a Jetpack Compose Android app.
When implementing a drawing surface that requires both wet and dry ink rendering.
When managing stroke history, undo/redo functionality, or persistent storage.
When configuring standard brush types and handling stroke geometry.

Advantages

Provides a consistent architecture for handling wet-to-dry ink transitions.
Ensures low-latency input processing through native Jetpack Ink integration.
Includes specific patterns to prevent UI flickering during stroke finalization.
Offers clear guidance on dependency management and build configuration.

Usage examples

“How do I set up the dependencies for Jetpack Ink in my Android project?”: The skill provides the necessary version catalog entries and build.gradle.kts configuration, including mandatory plugins for KSP and serialization.
“How can I implement a drawing surface that supports both wet and dry ink?”: The skill provides a complete DrawingSurface composable that stacks an InProgressStrokes layer over a Canvas, using a pendingStrokes buffer to prevent flickering.

Install

Download the skill as a ZIP:
https://mp-staging.autogineer.com/agent-skills/android/ink-app-builder/download

Unzip it into the cross-client skills folder of your project:

mkdir -p .agents/skills && unzip ink-app-builder.zip -d .agents/skills

Documentation by Google LLC

The Android Ink API (androidx.ink) is a modular Jetpack library for building high-performance, low-latency freehand drawing experiences on Android. It uses a wet ink and dry ink two-phase model:

Wet ink : Real-time, ultra-low-latency rendering while the user is drawing, handled by the InProgressStrokes composable.
Dry ink : Finalized, immutable Stroke objects rendered by the app using CanvasStrokeRenderer.

Setup and dependencies

The Ink API requires minSdk = 26 , which corresponds to Android 8.0 (API level 26) and higher. All androidx.ink modules MUST share an identical version in gradle/libs.versions.toml. Ask user permission before modifying project build files.

Version selection (`1.0.0` stable versus `1.1.0-alpha03` and higher)

Use 1.0.0 (Stable) for production apps that rely on StockBrushes or pre-serialized .brush assets decoded with BrushFamily.decode. In 1.0.0 stable, BrushFamily.encode, BrushFamily.decode, AndroidBrushFamilySerialization, and BrushFamilyDecodeCallback require @OptIn(ExperimentalInkCustomBrushApi::class).
Use 1.1.0-alpha03 and higher when the app constructs programmatic custom brushes (BrushFamily, BrushCoat, BrushTip, BrushPaint, BrushBehavior) in Kotlin code. Starting in 1.1.0-alpha02 and higher, BrushFamily serialization requires no @OptIn (and in 1.1.0-alpha05 and higher, ExperimentalInkCustomBrushApi is @RestrictTo(LIBRARY_GROUP), so NEVER annotate 1.1.0-alpha03 and higher code with it).

Version catalog (`gradle/libs.versions.toml`)

[versions]
ink = "<latest_version>"
inputMotionPrediction = "<latest_version>"

[libraries]
# Core Ink modules
androidx-ink-authoring         = { module = "androidx.ink:ink-authoring",         version.ref = "ink" }
androidx-ink-brush             = { module = "androidx.ink:ink-brush",             version.ref = "ink" }
androidx-ink-geometry          = { module = "androidx.ink:ink-geometry",          version.ref = "ink" }
androidx-ink-nativeloader      = { module = "androidx.ink:ink-nativeloader",      version.ref = "ink" }
androidx-ink-rendering         = { module = "androidx.ink:ink-rendering",         version.ref = "ink" }
androidx-ink-strokes           = { module = "androidx.ink:ink-strokes",           version.ref = "ink" }
androidx-ink-storage           = { module = "androidx.ink:ink-storage",           version.ref = "ink" }

# Compose integration modules
androidx-ink-authoring-android = { module = "androidx.ink:ink-authoring-android", version.ref = "ink" }
androidx-ink-authoring-compose = { module = "androidx.ink:ink-authoring-compose", version.ref = "ink" }
androidx-ink-brush-compose     = { module = "androidx.ink:ink-brush-compose",     version.ref = "ink" }
androidx-ink-geometry-compose  = { module = "androidx.ink:ink-geometry-compose",  version.ref = "ink" }

# Motion prediction (required for low-latency stylus tracking)
androidx-input-motionprediction = { module = "androidx.input:input-motionprediction", version.ref = "inputMotionPrediction" }

# Persistence (kotlinx.serialization + Room with KSP)
kotlinx-serialization-json = { module = "org.jetbrains.kotlinx:kotlinx-serialization-json", version.ref = "kotlinxSerialization" }
androidx-room-runtime      = { module = "androidx.room:room-runtime",  version.ref = "room" }
androidx-room-ktx          = { module = "androidx.room:room-ktx",      version.ref = "room" }
androidx-room-compiler     = { module = "androidx.room:room-compiler", version.ref = "room" }

[plugins]
kotlin-serialization = { id = "org.jetbrains.kotlin.plugin.serialization", version.ref = "kotlin" }
ksp                  = { id = "com.google.devtools.ksp",                   version.ref = "ksp" }

App module configuration (`app/build.gradle.kts`)

plugins {
    alias(libs.plugins.android.application)
    alias(libs.plugins.kotlin.compose)
    alias(libs.plugins.kotlin.serialization)
    alias(libs.plugins.ksp) // Mandatory when using Room in Kotlin
}

android {
    defaultConfig {
        minSdk = 26
    }
    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_17
        targetCompatibility = JavaVersion.VERSION_17
    }
    buildFeatures {
        compose = true
    }
}

dependencies {
    implementation(libs.androidx.ink.authoring)
    implementation(libs.androidx.ink.brush)
    implementation(libs.androidx.ink.geometry)
    implementation(libs.androidx.ink.nativeloader)
    implementation(libs.androidx.ink.rendering)
    implementation(libs.androidx.ink.strokes)
    implementation(libs.androidx.ink.storage)

    implementation(libs.androidx.ink.authoring.android)
    implementation(libs.androidx.ink.authoring.compose)
    implementation(libs.androidx.ink.brush.compose)
    implementation(libs.androidx.ink.geometry.compose)

    implementation(libs.androidx.input.motionprediction)

    implementation(libs.kotlinx.serialization.json)
    implementation(libs.androidx.room.runtime)
    implementation(libs.androidx.room.ktx)
    ksp(libs.androidx.room.compiler) // NEVER use annotationProcessor in Kotlin
}

Core drawing surface and default brush

Create a standard pressure-sensitive pen Brush with Brush.createWithComposeColor (from ink-brush-compose). The epsilon parameter defines the minimum distance between two input points, in stroke-space units, to be considered visually distinct (0.1f for general drawing, 0.01f for fine precision tools; Brush enforces 0f < epsilon <= size):

/**
 * Creates a default pressure-sensitive pen [Brush].
 *
 * The `epsilon` parameter sets the geometric tolerance (minimum point distance
 * in stroke units) controlling how far a stroke can be zoomed before triangle
 * artifacts appear (`0f < epsilon <= size`).
 */
fun createDefaultPenBrush(): Brush {
    return Brush.createWithComposeColor(
        family = StockBrushes.pressurePen(),
        color = Color.Black,
        size = 5f,
        epsilon = 0.1f,
    )
}

<br />

Stack two layers inside a Box for the drawing surface: a Compose Canvas that renders finalized dry Stroke objects inside nativeCanvas.withSave using CanvasStrokeRenderer, and an InProgressStrokes composable on top for low-latency wet ink capture. Encapsulate a synchronous pendingStrokes Compose Snapshot State buffer inside DrawingSurface so the dry Canvas invalidates in the exact same UI thread run loop when onStrokesFinished fires, preventing a 1-frame wet-to-dry flicker:

@Composable
fun DrawingSurface(
    strokes: List<Stroke>,
    canvasStrokeRenderer: CanvasStrokeRenderer,
    currentBrush: Brush,
    onGetNextBrush: () -> Brush,
    onStrokesFinished: (List<Stroke>) -> Unit,
    isEraserMode: Boolean,
    modifier: Modifier = Modifier,
    textureStore: AppTextureBitmapStore = LocalTextureStore.current,
    onErase: (Float, Float) -> Unit = { _, _ -> },
    onEraseStart: () -> Unit = {},
    onEraseEnd: () -> Unit = {},
) {
    val cacheGen by textureStore.generation.collectAsStateWithLifecycle()

    // Holds newly finished strokes synchronously for the single frame before
    // asynchronous StateFlow collection delivers the updated strokes list.
    var pendingStrokes by remember { mutableStateOf<List<Stroke>>(emptyList()) }

    SideEffect {
        if (pendingStrokes.isNotEmpty()) {
            pendingStrokes = if (strokes.isEmpty()) {
                emptyList()
            } else {
                pendingStrokes.filter { pending -> strokes.none { it === pending } }
            }
        }
    }

    val strokesToDraw = remember(strokes, pendingStrokes) {
        if (pendingStrokes.isEmpty()) {
            strokes
        } else {
            strokes + pendingStrokes.filter { pending -> strokes.none { it === pending } }
        }
    }
    val identityMatrix = remember { Matrix() }

    val currentOnErase by rememberUpdatedState(onErase)
    val currentOnEraseStart by rememberUpdatedState(onEraseStart)
    val currentOnEraseEnd by rememberUpdatedState(onEraseEnd)

    Box(modifier = modifier) {
        // Layer 1: Dry ink - completed strokes + same-frame pending handoff strokes
        Canvas(modifier = Modifier.fillMaxSize()) {
            val nativeCanvas = drawContext.canvas.nativeCanvas
            strokesToDraw.fastForEach { stroke ->
                nativeCanvas.withSave {
                    canvasStrokeRenderer.draw(
                        canvas = this,
                        stroke = stroke,
                        strokeToScreenTransform = identityMatrix,
                    )
                }
            }
        }

        // Layer 2: Eraser touch handler OR Wet ink (InProgressStrokes)
        if (isEraserMode) {
            Box(
                modifier = Modifier
                    .fillMaxSize()
                    .pointerInput(Unit) {
                        detectDragGestures(
                            onDragStart = { currentOnEraseStart() },
                            onDragEnd = { currentOnEraseEnd() },
                            onDragCancel = { currentOnEraseEnd() },
                            onDrag = { change, _ ->
                                currentOnErase(change.position.x, change.position.y)
                                change.consume()
                            },
                        )
                    }
            )
        } else {
            key(cacheGen) {
                InProgressStrokes(
                    defaultBrush = currentBrush,
                    nextBrush = onGetNextBrush,
                    onStrokesFinished = { newStrokes ->
                        pendingStrokes = pendingStrokes + newStrokes
                        onStrokesFinished(newStrokes)
                    },
                    textureBitmapStore = textureStore,
                )
            }
        }
    }
}

<br />

Workflow and task routing

Follow these conditional instructions based on the requested task:

Step 1 (Dependencies and SDK setup) : When adding Ink API dependencies or configuring minSdk, follow the setup blocks in this file and the Ink API setup guide. Verify that ink-nativeloader, ink-authoring-android, and androidx.input:input-motionprediction are present.
Step 2 (Drawing surface and stroke rendering) : When creating a Compose drawing screen with wet ink (InProgressStrokes) and dry ink (CanvasStrokeRenderer), implement DrawingSurface from this file and review Draw a stroke. For InProgressStrokes parameter details, BlendMode.Multiply highlighter layer compositing, and TextureBitmapStore generation invalidation, you MUST follow drawing-and-brushes.md.
Step 3 (Stock brushes and brush switching) : When creating, modifying, or switching stock brushes (StockBrushes.pressurePen, marker, highlighter, dashedLine, or emojiHighlighter), review Brush APIs and you MUST follow drawing-and-brushes.md for epsilon geometry constraints, highlighter alpha preservation, and Android 14 (API level 34) emojiHighlighter rules.
Step 4 (Eraser, undo and redo, and MVVM architecture) : When implementing a geometry-based stroke eraser, linear undo and redo history stacks, or MVVM ViewModel and Hilt wiring, review Geometry APIs and you MUST follow editing-and-architecture.md.
Step 5 (Persistence, bitmap export, and gesture coexistence) : When saving and loading strokes with Room (StrokeInputBatch.encode and decode), preserving UI state across configuration changes, exporting drawings to a Bitmap or PNG file, or combining long-press drag gestures with drawing (pointerInputWithSiblingFallthrough), review State preservation and persistent storage and you MUST follow persistence-and-advanced.md.
Programmatic custom brushes : For custom BrushFamily creation, custom tip shapes, or behavior node graphs, suggest the ink-custom-brush-builder skill.

Antipatterns

NEVER use InProgressStrokesView in Compose screens ---that's the View-based API. Use the InProgressStrokes composable instead.
NEVER omit ink-nativeloader or ink-authoring-android ---missing ink-nativeloader throws UnsatisfiedLinkError, and missing ink-authoring-android throws ClassNotFoundException at runtime.
NEVER use View.OnTouchListener or MotionEvent directly ---the InProgressStrokes composable captures and processes touch and stylus input internally.
NEVER draw strokes manually with Canvas.drawPath or by iterating stroke points---always call CanvasStrokeRenderer.draw(canvas, stroke, transform).
NEVER call CanvasStrokeRenderer.create(forcePathRendering = true) ---the 2-argument forcePathRendering overload is @RestrictTo(LIBRARY_GROUP). Use the public CanvasStrokeRenderer.create(textureStore) factory, which automatically detects software Bitmap canvases and falls back to path rendering.
NEVER rely solely on asynchronous StateFlow collection in onStrokesFinished ---InProgressStrokes removes completed wet strokes immediately after onStrokesFinished returns on the UI thread, while collectAsStateWithLifecycle updates on a later run loop, causing a 1-frame wet-to-dry flicker. Always mutate Compose Snapshot State synchronously in the same UI thread run loop using a pendingStrokes buffer as shown in DrawingSurface.
NEVER store strokes as bitmaps for undo, redo, or database persistence---store Stroke objects in memory and serialize StrokeInputBatch bytes with brush metadata for disk storage.
NEVER use annotationProcessor for Room in Kotlin ---always apply the com.google.devtools.ksp plugin and use ksp(libs.androidx.room.compiler) to avoid AppDatabase_Impl does not exist crashes at launch.

Files

ATTRIBUTION.mdAdded by AutoGineer982 B
LICENSELicence file added by AutoGineer11.1 KiB
SKILL.md15.3 KiB
references/android/develop/ui/compose/touch-input/stylus-input/ink-api-brush-apis.md5.0 KiB
references/android/develop/ui/compose/touch-input/stylus-input/ink-api-draw-stroke.md2.1 KiB
references/android/develop/ui/compose/touch-input/stylus-input/ink-api-geometry-apis.md1.2 KiB
references/android/develop/ui/compose/touch-input/stylus-input/ink-api-setup.md1.2 KiB
references/android/develop/ui/compose/touch-input/stylus-input/ink-api-state-preservation.md11.9 KiB
references/drawing-and-brushes.md9.0 KiB
references/editing-and-architecture.md10.2 KiB
references/persistence-and-advanced.md10.6 KiB

Requirements and compatibility

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.

Needs: Needs Node.js

Security

No issues found by our static scan· No issues found

A static scan is not a guarantee. Skills are third-party content: review a skill before you let an agent use it.

Attribution and licence

Created by

Google LLC

Publisher

Android (Google) (Official)

Distributed by

Android (Google)

Source

android/skills · jetpack-compose/ink/ink-app-builder · commit bf68e2d

Licence

Apache License 2.0 (redistribution allowed)

LICENSE (added by AutoGineer from LICENSE.txt)
ATTRIBUTION.md (written by AutoGineer)

Synced

2026-11-08

AutoGineer is not affiliated with or endorsed by Google LLC or Android (Google).

Download ZIP

The ZIP holds the skill’s files, its licence files and an ATTRIBUTION.md. Download ink-app-builder.zip

From the author

AutoGineer summary

What it does

When to use it

Advantages

Usage examples

Install

Documentation by Google LLC

Setup and dependencies

Version selection (1.0.0 stable versus 1.1.0-alpha03 and higher)

Version catalog (gradle/libs.versions.toml)

App module configuration (app/build.gradle.kts)

Core drawing surface and default brush

Workflow and task routing

Antipatterns

Files

Requirements and compatibility

Security

Attribution and licence

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Download ZIP

Version selection (`1.0.0` stable versus `1.1.0-alpha03` and higher)

Version catalog (`gradle/libs.versions.toml`)

App module configuration (`app/build.gradle.kts`)