iShapeKit

2D polygon geometry for Swift, powered by the Rust iOverlay and iTriangle libraries through iShape-ffi. Use it in drawing apps, vector editors, map tools, or games to combine shapes, build outlines, and prepare convex polygons for collision geometry.

The package provides native CGPoint and integer APIs with a bundled XCFramework. Rust handles the geometry; Swift manages the library handles. You can use it without installing Rust, and reuse flat buffers to reduce allocations in repeated operations.

Features

Task	API
Union, intersection, difference, XOR; polygons with holes	FloatOverlay, IntOverlay
Expand or shrink closed shapes	CGPointOutlineOffset
Stroke paths with constant or per-vertex width	CGPointStrokeOffset, CGPointVariableStrokeOffset
Stroke a CGPath made of line segments	CGPathBuffering
Split shapes into non-overlapping convex polygons	CGPointConvexDecomposition
Get nesting links between Boolean result shapes	FloatOverlay.overlayHierarchy

Installation

Requires Swift 6.2+, iOS 16+ or macOS 11+. Add version 0.2.7 through Swift Package Manager:

dependencies: [
    .package(url: "https://github.com/iShape-Rust/iShape-swift.git", from: "0.2.7")
],
targets: [
    .target(
        name: "YourTarget",
        dependencies: [.product(name: "iShapeKit", package: "iShape-swift")]
    )
]

Quick start

Combine two rectangles:

import CoreGraphics
import iShapeKit

let subject: CGPointShape = [[
    CGPoint(x: 0, y: 0), CGPoint(x: 4, y: 0),
    CGPoint(x: 4, y: 4), CGPoint(x: 0, y: 4)
]]
let clip: CGPointShape = [[
    CGPoint(x: 2, y: 0), CGPoint(x: 6, y: 0),
    CGPoint(x: 6, y: 4), CGPoint(x: 2, y: 4)
]]

let overlay = FloatOverlay()
overlay.addSubject([subject])
overlay.addClip([clip])

if let shapes = overlay.overlay(overlayRule: .union, fillRule: .evenOdd) {
    print(shapes.count) // 1 merged shape
}

// Expand a shape or split it into convex pieces.
let expanded = CGPointOutlineOffset.offsetShape(shape: subject, distance: 1)
let convex = CGPointConvexDecomposition.toConvexPolygons(shape: subject)

A contour is [CGPoint]; a shape is an array of contours (outer boundary followed by holes); a shapes collection is an array of shapes. Contours are implicitly closed. Use .evenOdd to interpret holes by nesting, or .nonZero with the appropriate contour winding.

For integer coordinates, use IntOverlay and IntPoint. For repeated calls, pass a reusable FlatShapesBuffer or FlatF64ShapesBuffer as the output. Buffer-based offsets and convex decomposition require distinct input and output buffers.

Outline offsets use positive distances to expand outer contours and negative distances to shrink them. Stroke distance is half the full width; variable-stroke vertices specify the full width. Joins and caps are configurable through OutlineOffsetStyle and StrokeOffsetStyle; angle parameters are in radians. CGPathBuffering accepts line segments only; flatten curves before passing them in.

Development

To rebuild the bundled libraries, keep iShape-ffi and iShape-swift as sibling directories. On macOS with Xcode and Rust installed, run from this repository:

./build_ffi.sh
swift build
swift test

The script builds macOS (arm64/x86_64), iOS devices (arm64), and iOS simulators (arm64/x86_64), then packages the static libraries into an XCFramework. Rebuild whenever the Rust implementation or C header changes.