🖌️ Compose Shape Fitter

Compose Shape Fitter is a lightweight Kotlin library for Jetpack Compose that approximates geometric shapes from a sequence of points and can render those points on a DrawScope. It’s ideal for gesture input, sketch recognition, and turning user strokes into meaningful primitives.

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✨ Features

• Approximate a best-fit shape from a list of Offset points
• Draw the original stroke (points) into a Compose DrawScope
• Simple, composable-first API

Currently Supported Shapes

• Circle
• Ellipse
• Hexagon
• Oriented Bounding Box (OBB)
• Pentagon
• Triangle
• Square

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Installation

Compose Shape Fitter is available on Maven Central.

Using Version Catalogs:

libs.versions.toml:

[versions]
composeShapeFitterVersion = "1.0.0"

[libraries]
composeShapeFitterLibrary = { group = "io.github.sarimmehdi", name = "compose-shape-fitter", version.ref = "composeShapeFitterVersion" }

build.gradle.kts (module-level):

implementation(libs.composeShapeFitterLibrary)

Gradle (Kotlin DSL - build.gradle.kts)::

implementation("io.github.sarimmehdi:compose-shape-fitter:1.0.0")

build.gradle (Groovy):

implementation 'io.github.sarimmehdi:compose-shape-fitter:1.0.0'

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🚀 Quick Start

Draw a user stroke (sequence of points)

val points: List<Offset> = /* collected from gesture/touch input */

draw(
    drawScope = drawScope,
    points = points
)

Get an approximated shape

val approximatedShape = getApproximatedShape(points)

when (approximatedShape) {
    is ApproximatedShape.CircleShape -> { /* handle circle */ }
    is ApproximatedShape.EllipseShape -> { /* handle ellipse */ }
    is ApproximatedShape.HexagonShape -> { /* handle hexagon */ }
    is ApproximatedShape.PentagonShape -> { /* handle pentagon */ }
    is ApproximatedShape.SquareShape -> { /* handle square */ }
    is ApproximatedShape.TriangleShape -> { /* handle triangle */ }
    is ApproximatedShape.ObbShape -> { /* handle OBB */ }
    is ApproximatedShape.SkewedEllipseShape -> { /* handle oriented ellipse */ }
    null -> { /* no recognizable shape */ }
}

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🧩 API Overview

fun draw(
    drawScope: DrawScope,
    points: List<Offset>,
)

fun getApproximatedShape(
    points: List<Offset>
): ApproximatedShape?

ApproximatedShape is a sealed type representing the supported shapes listed above.

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🧠 Typical Use Cases

• Freehand shape recognition in drawing or note apps
• Gesture-based UI controls (e.g., draw a triangle to trigger an action)
• Educational tools for geometry and sketch classification

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🛣️ Roadmap

• Support for triangle variants (isosceles, equilateral, scalene)
• Line fitting: linear, quadratic, and spline matching for polylines
• Overlap percentage between different shapes

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🤝 Contributing

Contributions are welcome!
Please open an issue to discuss your idea or submit a PR with tests and a brief description.