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Ink Custom Brush Builder

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

  • Skill
  • Tool integration
  • Software development
  • Apache-2.0
  • No issues found
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From the author

Creates custom BrushFamily definitions for an Android app using Jetpack Ink (androidx.ink 1.1.0-alpha03 and higher). Use this skill when configuring custom BrushTip shapes, adding pressure, tilt, speed, or noise sensitivity using BrushBehavior node graphs, creating multi-coat layered brushes, applying tiling or particle stamping textures, configuring SlidingWindowModel input smoothing, or serializing brushes. Delivers complete Kotlin BrushFamily, BrushCoat, BrushTip, BrushPaint, and BrushBehavior implementations. Don't use for View-based (XML) inking, Compose drawing surface setup, or stock brush selection. For Compose drawing surface setup, InProgressStrokes wet and dry rendering, eraser, or persistence, suggest the ink-app-builder skill.
— the description by Google LLC

AutoGineer summary

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

The ink-custom-brush-builder skill provides a structured approach to creating programmatic custom brushes for Android applications utilizing the Jetpack Ink library (version 1.1.0-alpha03 and higher). It enables developers to define complex brush behaviors, multi-coat layers, and custom textures using Kotlin constructors rather than manual protocol buffer builders. The skill covers the entire brush hierarchy, including BrushFamily, BrushCoat, BrushTip, BrushPaint, and BrushBehavior node graphs, ensuring developers can implement responsive, high-fidelity drawing tools with features like pressure, tilt, and speed sensitivity.

What it does

  • Generates complete Kotlin implementations for BrushFamily, BrushCoat, BrushTip, BrushPaint, and BrushBehavior.
  • Configures dynamic stylus and touch responses using BrushBehavior node graphs.
  • Applies tiling or particle stamping textures to brushes.
  • Sets up input smoothing via SlidingWindowModel.
  • Provides guidance on encoding and decoding custom BrushFamily definitions.
  • Ensures correct dependency versions for Jetpack Ink libraries.

When to use it

  • When you need to create custom brush styles beyond the provided stock brushes.
  • When implementing brushes that respond dynamically to stylus pressure, tilt, or speed.
  • When building multi-coat layered brushes with specific texture or color functions.
  • When you need to serialize and deserialize custom brush definitions.
  • When configuring specific input smoothing for drawing strokes.

Advantages

  • Uses public Kotlin constructors for type-safe brush definition.
  • Enables complex, organic stroke behaviors through procedural noise and response nodes.
  • Supports advanced texture mapping without manual bitmap shader implementation.
  • Provides a consistent, documented workflow for brush structure and behavior.
  • Avoids common antipatterns like manual Bézier smoothing or raw proto builders.

Usage examples

“How do I create a custom pressure-sensitive pen brush?”
The agent will provide a Kotlin code snippet using BrushFamily, BrushCoat, and a BrushBehavior node graph that maps NORMALIZED_PRESSURE to SIZE_MULTIPLIER.
“Help me add a grain texture to my custom brush.”
The agent will guide you through implementing a BrushPaint.TilingTexture, identifying the necessary drawable resource, and registering it in the TextureBitmapStore.

Install

  1. Download the skill as a ZIP:

    https://autogineer.com/agent-skills/android/ink-custom-brush-builder/download

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

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

Documentation by Google LLC

Custom brushes in the Android Ink API are built around the BrushFamily hierarchy:

BrushFamily
├── InputModel (BrushFamily.InputModel.SlidingWindowModel or PASSTHROUGH_MODEL)
└── BrushCoat[] (one or more rendering layers)
    ├── BrushTip (shape: scaleX, scaleY, cornerRounding, rotationDegrees, slantDegrees, pinch)
    │   └── BrushBehavior[] (dynamic response to stylus or touch input)
    │       └── Tree: TargetNode(input = [Operators](input = SourceNode))
    └── BrushPaint (visual appearance)
        ├── SelfOverlap (ANY, ACCUMULATE, or DISCARD)
        ├── TextureLayer[] (BrushPaint.TilingTexture or BrushPaint.StampingTexture)
        └── BrushPaint.ColorFunction[] (OpacityMultiplier or ReplaceColor)

Create a Brush by combining a custom BrushFamily with a Compose Color, size, and epsilon:

val brush = Brush.createWithComposeColor(
    family = myCustomFamily,
    color = Color.Black,
    size = 10f,
    epsilon = 0.1f,
)

<br />

Version and experimental API requirements :

  • Requires androidx.ink 1.1.0-alpha03 and higher : In 1.0.0 (Stable) and 1.1.0-alpha01-alpha02, BrushFamily(...), BrushCoat, BrushTip, BrushPaint, BrushBehavior, and androidx.ink.brush.behavior.* nodes were @RestrictTo(LIBRARY_GROUP) (in 1.0.0 stable, custom brushes can only be loaded from binary proto streams using BrushFamily.decode). Starting in 1.1.0-alpha03 and higher , programmatic custom brush constructors graduated to public API (BrushPaint.TilingTexture, BrushPaint.StampingTexture, BrushPaint.ColorFunction, BrushFamily.InputModel.SlidingWindowModel, and all behavior nodes).

  • No @OptIn required in 1.1.0-alpha03 and higher : All public custom brush classes and ink-storage BrushFamily serialization APIs (BrushFamily.encode and decode, AndroidBrushFamilySerialization, BrushFamilyDecodeCallback) are unannotated in 1.1.0-alpha03 and higher (ExperimentalInkCustomBrushApi is @RestrictTo(LIBRARY_GROUP) in 1.1.0-alpha05 and higher, and is only required on BrushFamily serialization in 1.0.0 stable).

Workflow and task routing

Follow these conditional instructions based on the requested custom brush task:

  • Step 1 (Dependencies) : When setting up an Android project for programmatic custom brushes, ask user permission before editing build files and verify that androidx.ink:ink-brush, androidx.ink:ink-brush-compose, androidx.ink:ink-storage, and androidx.ink:ink-nativeloader use version 1.1.0-alpha03 or higher in gradle/libs.versions.toml and app/build.gradle.kts.

  • Step 2 (Hierarchy, tip shape, paint, and input smoothing) : When defining BrushFamily and multi-coat BrushCoat layers, configuring BrushTip geometry (scaleX, scaleY, cornerRounding, rotationDegrees, slantDegrees, pinch), setting BrushPaint properties (SelfOverlap, ColorFunction), or smoothing stroke input with BrushFamily.InputModel.SlidingWindowModel, you MUST follow brush-structure.md. For baseline Brush creation or 1.0.0 resource loading, review Brush APIs.

  • Step 3 (Dynamic stylus and touch behaviors) : When making a brush respond dynamically to stylus pressure, tilt, speed, direction, or procedural noise using BrushBehavior node trees (SourceNode, DampingNode, NoiseNode, ResponseNode, TargetNode, PolarTargetNode), you MUST follow brush-behaviors.md.

  • Step 4 (Textures and serialization) : When adding BrushPaint.TilingTexture or BrushPaint.StampingTexture layers, implementing TextureBitmapStore, or encoding and decoding custom BrushFamily definitions (BrushFamily.encode and decode, AndroidBrushFamilySerialization, BrushFamilyDecodeCallback), you MUST follow textures-and-serialization.md. Inform the user which texture image files (such as app/src/main/res/drawable-nodpi/pencil_grain.png) to add to their project and register in TextureBitmapStore.

  • Step 5 (Complete brush recipes) : When building a complete pressure pen, calligraphy nib, shading pencil, watercolor wash, or multi-coat shadow brush from scratch, start from the copy-ready implementations in examples.md.

  • Compose drawing surface, eraser, or persistence : For Compose drawing surface setup, InProgressStrokes wet and dry rendering, geometry-based erasing, or Room stroke persistence, suggest the ink-app-builder skill.

Antipatterns

  • NEVER use raw ink.proto.* builders to construct brushes---always use the public Kotlin constructors (BrushFamily, BrushCoat, BrushTip, BrushPaint, BrushBehavior from androidx.ink.brush.*).

  • NEVER manually scale stroke width in a touch listener for pressure or tilt sensitivity---use BrushBehavior mapping SourceNode.Source.NORMALIZED_PRESSURE or TILT_IN_RADIANS to TargetNode.Target.SIZE_MULTIPLIER or WIDTH_MULTIPLIER.

  • NEVER use manual Canvas bitmap stamping or BitmapShader for textured brushes---use BrushPaint.TilingTexture or BrushPaint.StampingTexture with a TextureBitmapStore.

  • NEVER use BlendMode.SRC_OVER on the final (or only) TextureLayer ---use BlendMode.MODULATE, DST_IN, DST_OUT, SRC_ATOP, or SRC_IN so edge anti-aliasing and OPACITY_MULTIPLIER behaviors aren't overridden.

  • NEVER serialize BrushFamily as JSON, Gson, Moshi, or Parcelable ---always use BrushFamily.encode and BrushFamily.decode or AndroidBrushFamilySerialization from androidx.ink.storage.

  • NEVER implement manual Bézier (quadTo, cubicTo) smoothing ---configure BrushFamily.InputModel.SlidingWindowModel for input smoothing and DampingNode for behavior smoothing.

  • NEVER use Random.nextFloat in draw loops for organic stroke wobble---attach a NoiseNode varied over stroke distance in BrushBehavior.

Files

references/textures-and-serialization.md

Reference for adding BrushPaint.TilingTexture and BrushPaint.StampingTexture layers with TextureBitmapStore, and encoding or decoding custom BrushFamily definitions (androidx.ink 1.1.0-alpha03 and higher).

TextureBitmapStore and texture assets

androidx.ink doesn't bundle texture image assets. When generating a textured brush, inform the user to add the referenced PNG or WebP texture file to their project (such as app/src/main/res/drawable-nodpi/pencil_grain.png to prevent density scaling) and return its Bitmap from TextureBitmapStore. If TextureBitmapStore[clientTextureId] returns null, the stroke silently renders as a flat, untextured fill.

class CustomBrushTextureStore(context: Context) : TextureBitmapStore {
    private val resources = context.resources
    private val textureResources: Map<String, Int> = mapOf(
        "pencil-grain" to R.drawable.pencil_grain,
        "watercolor-wash" to R.drawable.watercolor_wash,
    )
    private val loadedBitmaps = mutableMapOf<String, Bitmap>()

    private val _generation = MutableStateFlow(0)
    val generation: StateFlow<Int> = _generation.asStateFlow()

    override operator fun get(clientTextureId: String): Bitmap? {
        return loadedBitmaps.getOrPut(clientTextureId) {
            textureResources[clientTextureId]?.let { resId ->
                BitmapFactory.decodeResource(resources, resId)
            } ?: return null
        }
    }

    fun registerBitmap(textureId: String, bitmap: Bitmap) {
        loadedBitmaps[textureId] = bitmap
        _generation.update { it + 1 }
    }
}

<br />

When generation increments after loading a texture dynamically (such as from a decoded .brush stream), recreate CanvasStrokeRenderer with remember(textureStore, generation) and re-key InProgressStrokes with key(generation) so cached BitmapShader instances refresh.

TextureLayer subclasses (TilingTexture and StampingTexture)

In 1.1.0-alpha03 and higher, BrushPaint.TextureLayer is an abstract class with two concrete subclasses:

  • BrushPaint.TilingTexture : Repeats a seamless texture across stroke geometry (ideal for pencil grain, paper texture, or watercolor wash). Set sizeUnit = BrushPaint.TextureLayer.SizeUnit.BRUSH_SIZE so tile dimensions scale with Brush.size.

  • BrushPaint.StampingTexture : Stamps a texture onto each discrete particle along a stroke (BrushTip.particleGapDistanceScale > 0f or particleGapDurationMillis > 0L). Requires CanvasMeshRenderer on Android 14 (API level 34) and higher hardware Canvas; supply a second path-compatible fallback BrushPaint in BrushCoat.paintPreferences if the stroke must also render on Android 13 (API level 33) and lower or software Canvas(bitmap).

Choose BlendMode for texture layers

The final (or only) TextureLayer blends the texture (src) against the brush color (dst, which carries edge anti-aliasing and per-vertex OPACITY_MULTIPLIER). Use a blend mode whose output alpha is proportional to Alpha_dst---such as BlendMode.MODULATE (default), BlendMode.DST_IN , BlendMode.DST_OUT , BlendMode.SRC_ATOP , or BlendMode.SRC_IN . Never use BlendMode.SRC_OVER on the final TextureLayer because it overrides edge anti-aliasing and ignores OPACITY_MULTIPLIER wherever the texture is opaque:

fun createTexturedBrushFamily(): BrushFamily {
    val grainPaint = BrushPaint(
        selfOverlap = SelfOverlap.ANY,
        textureLayers = listOf(
            BrushPaint.TilingTexture(
                clientTextureId = "pencil-grain",
                sizeX = 1.0f,
                sizeY = 1.0f,
                sizeUnit = BrushPaint.TextureLayer.SizeUnit.BRUSH_SIZE,
                blendMode = BrushPaint.TextureLayer.BlendMode.MODULATE,
            ),
        ),
        colorFunctions = listOf(BrushPaint.ColorFunction.OpacityMultiplier(0.85f)),
    )

    return BrushFamily(
        tip = BrushTip(scaleX = 1f, scaleY = 1f, cornerRounding = 1f),
        paint = grainPaint,
    )
}

<br />

Serialize and deserialize custom BrushFamily definitions

androidx.ink.storage provides two equivalent gzipped-protobuf serialization APIs (unannotated in 1.1.0-alpha02 and higher; requires @OptIn(ExperimentalInkCustomBrushApi::class) only on 1.0.0 stable):

  1. Kotlin extensions : brushFamily.encode(outputStream, textureBitmapStore) and BrushFamily.decode(inputStream, maxVersion, getClientTextureId).

  2. Java-friendly @JvmStatic methods : AndroidBrushFamilySerialization.encode and AndroidBrushFamilySerialization.decode.

Save and load a BrushFamily with embedded textures

When decoding with a texture callback in 1.1.0-alpha, always wrap the lambda in BrushFamilyDecodeCallback { textureId, bitmap -> ... } to disambiguate from the multiplatform OnDecodeTexturePngBytes overload. Pass maxVersion = Version.MAX_SUPPORTED for production brushes or Version.DEVELOPMENT when testing experimental brush features:

suspend fun saveCustomBrushToFile(
    context: Context,
    uri: Uri,
    brushFamily: BrushFamily,
    textureBitmapStore: TextureBitmapStore,
) = withContext(Dispatchers.IO) {
    context.contentResolver.openOutputStream(uri)?.use { outputStream ->
        brushFamily.encode(outputStream, textureBitmapStore)
    }
}

suspend fun loadCustomBrushFromFile(
    inputStream: InputStream,
    textureStore: CustomBrushTextureStore,
    allowDevelopmentFeatures: Boolean = false,
): BrushFamily = withContext(Dispatchers.IO) {
    val maxVersion = if (allowDevelopmentFeatures) {
        Version.DEVELOPMENT
    } else {
        Version.MAX_SUPPORTED
    }
    inputStream.use { stream ->
        BrushFamily.decode(
            input = stream,
            maxVersion = maxVersion,
            getClientTextureId = BrushFamilyDecodeCallback { textureId, bitmap ->
                if (bitmap != null) {
                    textureStore.registerBitmap(textureId, bitmap)
                }
                textureId
            },
        )
    }
}

<br />

Store custom brushes in a Room database (BLOB)

Persist encoded BrushFamily bytes in a ColumnInfo.BLOB ByteArray column:

@Entity(tableName = "custom_brushes")
data class CustomBrushEntity(
    @PrimaryKey val name: String,
    @ColumnInfo(typeAffinity = ColumnInfo.BLOB)
    val brushBytes: ByteArray,
) {
    override fun equals(other: Any?): Boolean {
        if (this === other) return true
        if (other !is CustomBrushEntity) return false
        return name == other.name && brushBytes.contentEquals(other.brushBytes)
    }

    override fun hashCode(): Int = 31 * name.hashCode() + brushBytes.contentHashCode()
}

fun encodeBrushForDatabase(
    brushFamily: BrushFamily,
    textureBitmapStore: TextureBitmapStore = TextureBitmapStore { null },
): ByteArray {
    return ByteArrayOutputStream().use { stream ->
        brushFamily.encode(stream, textureBitmapStore)
        stream.toByteArray()
    }
}

<br />

Common pitfalls

  • Instantiating abstract BrushPaint.TextureLayer directly : In 1.1.0-alpha03 and higher, instantiate BrushPaint.TilingTexture or BrushPaint.StampingTexture (SizeUnit, BlendMode, and Wrap remain nested on BrushPaint.TextureLayer.*, while Origin is nested on BrushPaint.TilingTexture.Origin).

  • Passing an untyped trailing lambda to BrushFamily.decode : Kotlin can't disambiguate between BrushFamilyDecodeCallback (Bitmap?) and OnDecodeTexturePngBytes (ByteArray?). Always wrap with BrushFamilyDecodeCallback { id, bitmap -> ... }.

  • Oversized texture bitmaps : Keep tiled textures around 256×256 or 512×512 pixels in res/drawable-nodpi/ to avoid unnecessary GPU memory consumption.

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-custom-brush-builder · commit bf68e2d
Licence
Apache License 2.0 (redistribution allowed)
  • LICENSE (added by AutoGineer from LICENSE.txt)
  • ATTRIBUTION.md (written by AutoGineer)
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AutoGineer is not affiliated with or endorsed by Google LLC or Android (Google).

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