js-angusj-clipper

Polygon and line clipping and offsetting library for Javascript/Typescript

a port of Angus Johnson's clipper to WebAssembly/Asm.js

Install it with npm install --save js-angusj-clipper

To support this project star it on github!

What is this?

A library to make polygon clipping (boolean operations) and offsetting fast on Javascript thanks to WebAssembly with a fallback to Asm.js, based on the excellent Polygon Clipping (also known as Clipper) library by Angus Johnson.

Why?

Because sometimes performance does matter and I could not find a javascript library as fast or as rock solid as the C++ version of Clipper.

As an example, the results of the benchmarks included on the test suite when running on my machine (node 17.9.0) are:

Note, pureJs is jsclipper, a pure JS port of the same library

    500 boolean operations over two circles of 5000 points each
      clipType: intersection, subjectFillType: evenOdd
        ✓ wasm (212 ms)
        ✓ asmJs (598 ms)
        ✓ pureJs (573 ms)
      clipType: union, subjectFillType: evenOdd
        ✓ wasm (267 ms)
        ✓ asmJs (666 ms)
        ✓ pureJs (663 ms)
      clipType: difference, subjectFillType: evenOdd
        ✓ wasm (232 ms)
        ✓ asmJs (575 ms)
        ✓ pureJs (573 ms)
      clipType: xor, subjectFillType: evenOdd
        ✓ wasm (296 ms)
        ✓ asmJs (681 ms)
        ✓ pureJs (779 ms)
    10000 boolean operations over two circles of 100 points each
      clipType: intersection, subjectFillType: evenOdd
        ✓ wasm (143 ms)
        ✓ asmJs (347 ms)
        ✓ pureJs (255 ms)
      clipType: union, subjectFillType: evenOdd
        ✓ wasm (181 ms)
        ✓ asmJs (417 ms)
        ✓ pureJs (265 ms)
      clipType: difference, subjectFillType: evenOdd
        ✓ wasm (159 ms)
        ✓ asmJs (339 ms)
        ✓ pureJs (239 ms)
      clipType: xor, subjectFillType: evenOdd
        ✓ wasm (186 ms)
        ✓ asmJs (404 ms)
        ✓ pureJs (262 ms)
    100 offset operations over a circle of 5000 points
      joinType: miter, endType: closedPolygon, delta: 5
        ✓ wasm (129 ms)
        ✓ asmJs (390 ms)
        ✓ pureJs (702 ms)
      joinType: miter, endType: closedPolygon, delta: 0
        ✓ wasm (34 ms)
        ✓ asmJs (140 ms)
        ✓ pureJs (108 ms)
      joinType: miter, endType: closedPolygon, delta: -5
        ✓ wasm (146 ms)
        ✓ asmJs (386 ms)
        ✓ pureJs (770 ms)
    5000 offset operations over a circle of 100 points
      joinType: miter, endType: closedPolygon, delta: 5
        ✓ wasm (74 ms)
        ✓ asmJs (161 ms)
        ✓ pureJs (278 ms)
      joinType: miter, endType: closedPolygon, delta: 0
        ✓ wasm (61 ms)
        ✓ asmJs (138 ms)
        ✓ pureJs (162 ms)
      joinType: miter, endType: closedPolygon, delta: -5
        ✓ wasm (109 ms)
        ✓ asmJs (271 ms)
        ✓ pureJs (659 ms)

More or less, the results for boolean operations over moderately big polygons are:

• Pure JS port of the Clipper library: ~1.0s, baseline
• This library (WebAssembly): ~0.4s
• This library (Asm.js): ~1.0s (mostly due to the emulation of 64-bit integer operations)

and for small polygons are:

• Pure JS port of the Clipper library: ~1.0s, baseline
• This library (WebAssembly): ~0.7s (due to the overhead of copying structures to/from JS/C++)
• This library (Asm.js): ~1.4s (mostly due to the emulation of 64-bit integer operations + the overhead of copying structures to/from JS/C++)

As for offsetting, the results for a moderately big polygon are:

• Pure JS port of the Clipper library: ~1s, baseline
• This library (WebAssembly): ~0.2s
• This library (Asm.js): ~0.5s

and for small polygons are:

• Pure JS port of the Clipper library: ~1s, baseline
• This library (WebAssembly): ~0.2s
• This library (Asm.js): ~0.5s

Getting started

// universal version
// import it with
import * as clipperLib from "js-angusj-clipper"; // es6 / typescript
// or
const clipperLib = require("js-angusj-clipper"); // nodejs style require

// web-only version (for example for angular 6+)
// import it with
import * as clipperLib from "js-angusj-clipper/web"; // es6 / typescript
// or
const clipperLib = require("js-angusj-clipper/web"); // nodejs style require

async function mainAsync() {
  // create an instance of the library (usually only do this once in your app)
  const clipper = await clipperLib.loadNativeClipperLibInstanceAsync(
    // let it autodetect which one to use, but also available WasmOnly and AsmJsOnly
    clipperLib.NativeClipperLibRequestedFormat.WasmWithAsmJsFallback
  );

  // create some polygons (note that they MUST be integer coordinates)
  const poly1 = [{ x: 0, y: 0 }, { x: 10, y: 0 }, { x: 10, y: 10 }, { x: 0, y: 10 }];

  const poly2 = [{ x: 10, y: 0 }, { x: 20, y: 0 }, { x: 20, y: 10 }, { x: 10, y: 10 }];

  // get their union
  const polyResult = clipper.clipToPaths({
    clipType: clipperLib.ClipType.Union,

    subjectInputs: [{ data: poly1, closed: true }],

    clipInputs: [{ data: poly2 }],

    subjectFillType: clipperLib.PolyFillType.EvenOdd
  });

  /* polyResult will be:
  [
    [
      { x: 0, y: 0 },
      { x: 20, y: 0 },
      { x: 20, y: 10 },
      { x: 0, y: 10 }
    ]
  ]
 */
}

mainAsync();

For an in-depth description of the library see:

• Overview
• API Reference
• FAQ