js-angusj-clipper

Polygon and line clipping and offsetting library for Javascript/Typescript

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

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

To support this project star it on github!

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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.

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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 9.10) 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 (432 ms)
    √ asmJs (1002 ms)
    √ pureJs (1183 ms)
  clipType: union, subjectFillType: evenOdd
    √ wasm (507 ms)
    √ asmJs (1058 ms)
    √ pureJs (1037 ms)
  clipType: difference, subjectFillType: evenOdd
    √ wasm (437 ms)
    √ asmJs (917 ms)
    √ pureJs (948 ms)
  clipType: xor, subjectFillType: evenOdd
    √ wasm (504 ms)
    √ asmJs (1053 ms)
    √ pureJs (1958 ms)
10000 boolean operations over two circles of 100 points each
  clipType: intersection, subjectFillType: evenOdd
    √ wasm (281 ms)
    √ asmJs (562 ms)
    √ pureJs (333 ms)
  clipType: union, subjectFillType: evenOdd
    √ wasm (332 ms)
    √ asmJs (653 ms)
    √ pureJs (362 ms)
  clipType: difference, subjectFillType: evenOdd
    √ wasm (299 ms)
    √ asmJs (570 ms)
    √ pureJs (326 ms)
  clipType: xor, subjectFillType: evenOdd
    √ wasm (346 ms)
    √ asmJs (644 ms)
    √ pureJs (368 ms)
100 offset operations over a circle of 5000 points
  joinType: miter, endType: closedPolygon, delta: 5
    √ wasm (201 ms)
    √ asmJs (612 ms)
    √ pureJs (1156 ms)
  joinType: miter, endType: closedPolygon, delta: 0
    √ wasm (59 ms)
    √ asmJs (181 ms)
    √ pureJs (184 ms)
  joinType: miter, endType: closedPolygon, delta: -5
    √ wasm (231 ms)
    √ asmJs (565 ms)
    √ pureJs (1209 ms)
5000 offset operations over a circle of 100 points
  joinType: miter, endType: closedPolygon, delta: 5
    √ wasm (149 ms)
    √ asmJs (280 ms)
    √ pureJs (413 ms)
  joinType: miter, endType: closedPolygon, delta: 0
    √ wasm (123 ms)
    √ asmJs (232 ms)
    √ pureJs (248 ms)
  joinType: miter, endType: closedPolygon, delta: -5
    √ wasm (235 ms)
    √ asmJs (499 ms)
    √ pureJs (1012 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): ~0.5s
• 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): ~1.0s (due to the overhead of copying structures to/from JS/C++)
• This library (Asm.js): ~2.0s (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): ~0.15s
• This library (Asm.js): ~0.56s

and for small polygons are:

• Pure JS port of the Clipper library: ~1s, baseline
• This library (WebAssembly): ~0.28s
• This library (Asm.js): ~0.65s

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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();

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For an in-depth description of the library see:

• Overview
• API Reference
• FAQ