ink-custom-brush-builder

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

kotlin

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

TILT_IN_RADIANS

TargetNode.Target.SIZE_MULTIPLIER

WIDTH_MULTIPLIER

NEVER use manual
Canvas
bitmap stamping or
BitmapShader
for textured brushes---use

BrushPaint.TilingTexture

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

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
```
.

ink-custom-brush-builder

NPX Install

Tags

SKILL.md Content

Workflow and task routing

Antipatterns