fix(polygon): Improve speed of Polygon.getSignedArea()

.github/workflows/test.yml

@@ -39,3 +39,7 @@ jobs:
         uses: coverallsapp/github-action@09b709cf6a16e30b0808ba050c7a6e8a5ef13f8d # v1.2.5
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Bench
+        run: |
+          yarn test bench

modules/polygon/src/polygon-utils.ts

@@ -110,20 +110,47 @@ export const DimIndex: Record<string, number> = {
  * @returns Signed area of the polygon.
  * https://en.wikipedia.org/wiki/Shoelace_formula
  */
-export function getPolygonSignedArea(points: NumericArray, options: PolygonParams = {}): number {
+export function getPolygonSignedArea(
+  points: NumericArray,
+  options: PolygonParams & {fast?: boolean} = {}
+): number {
   const {start = 0, end = points.length, plane = 'xy'} = options;
   const dim = options.size || 2;
-  let area = 0;
   const i0 = DimIndex[plane[0]];
   const i1 = DimIndex[plane[1]];
 
+  let area = 0;
   for (let i = start, j = end - dim; i < end; i += dim) {
     area += (points[i + i0] - points[j + i0]) * (points[i + i1] + points[j + i1]);
     j = i;
   }
   return area / 2;
 }
 
+export function getPolygonSignedAreaFlatFast(
+  points: NumericArray,
+  options: PolygonParams = {}
+): number {
+  // const {start = 0} = options; TODO - fast
+  if (options.start) {
+    throw new Error('start option is not supported in fast mode');
+  }
+  const {end = points.length, plane = 'xy'} = options;
+  const dim = options.size || 2;
+  const i0 = DimIndex[plane[0]];
+  const i1 = DimIndex[plane[1]];
+
+  const Area = function (curr: number, prev: number): number {
+    return (points[curr + i0] - points[prev + i0]) * (points[curr + i1] - points[prev + i1]);
+  };
+
+  let area = Area(0, end - dim);
+  for (let i = dim; i < end; i += dim) {
+    area += Area(i, i - dim);
+  }
+  return area / 2;
+}
+
 /**
  * Calls the visitor callback for each segment in the polygon.
  * @param points An array that represents points of the polygon

modules/polygon/src/polygon.ts

@@ -9,6 +9,7 @@ import type {NumericArray} from '@math.gl/core';
 
 import {
   getPolygonSignedArea,
+  getPolygonSignedAreaFlatFast,
   forEachSegmentInPolygon,
   modifyPolygonWindingDirection,
   getPolygonSignedAreaPoints,
@@ -46,10 +47,12 @@ export class Polygon {
    * Returns signed area of the polygon.
    * @returns Signed area of the polygon.
    */
-  getSignedArea(): number {
-    if (this.isFlatArray) return getPolygonSignedArea(this.points as NumericArray, this.options);
-
-    return getPolygonSignedAreaPoints(this.points as number[][], this.options);
+  getSignedArea(fast?: boolean): number {
+    return this.isFlatArray
+      ? fast
+        ? getPolygonSignedAreaFlatFast(this.points as NumericArray, this.options)
+        : getPolygonSignedArea(this.points as NumericArray, this.options)
+      : getPolygonSignedAreaPoints(this.points as number[][], this.options);
   }
 
   /**

modules/polygon/test/bench.ts

@@ -8,15 +8,23 @@
 // @ts-nocheck
 import {earcut, Polygon, modifyPolygonWindingDirection, WINDING} from '@math.gl/polygon';
 import {toNested} from './utils';
+import {fstat} from 'fs';
 
-const polygonSmall = [0, 0, 1, 1, 0, 2, -1, 1, -1.25, 0.5, 0, 0];
+const flatPolygonSmall = [0, 0, 1, 1, 0, 2, -1, 1, -1.25, 0.5, 0, 0];
 
-const polygonMedium = [
+const flatPolygonMedium = [
   4.2625, 2.24125, 3.0025, 3.20125, 2.5225, 4.22125, 0.9225, 4.32125, -0.3775, 3.30125, -0.7975,
   2.14125, -1.8575, 2.72125, -1.8575, 0.64125, -0.3775, -0.89875, -0.3775, -0.89875, 1.2825,
   0.92125, 1.4025, -0.89875, 2.9025, -0.31875, 4.0825, 0.62125, 4.2625, 2.24125
 ];
-const polygonMediumNested = toNested(polygonMedium);
+const nestedPolygonMedium = toNested(flatPolygonMedium);
+
+const flatPolygonLarge = new Array(10000)
+  .fill(0)
+  .map((_, i) =>
+    i % 2 === 0 ? Math.cos((Math.PI * 2 * i) / 5000) : Math.sin((Math.PI * 2 * i) / 5000)
+  );
+const nestedPolygonLarge = toNested(flatPolygonLarge);
 
 // A helper function to swap winding direction on each iteration.
 let winding = WINDING.CLOCKWISE;
@@ -28,44 +36,68 @@ function nextWinding() {
 export function polygonBench(suite, addReferenceBenchmarks) {
   suite
     .group('Polygon')
-    .add('Polygon#new()', () => new Polygon(polygonSmall))
-    .add('Polygon#modifyWindingDirection() S', () => {
-      const polygon = new Polygon(polygonSmall);
+    .add('Polygon#new()', () => new Polygon(flatPolygonSmall))
+    .add('Polygon#modifyWindingDirection() flat small', () => {
+      const polygon = new Polygon(flatPolygonSmall);
       polygon.modifyWindingDirection(nextWinding());
     })
-    .add('modifyPolygonWindingDirection() S', () => {
-      modifyPolygonWindingDirection(polygonSmall, nextWinding(), {
+    .add('modifyPolygonWindingDirection() flat small', () => {
+      modifyPolygonWindingDirection(flatPolygonSmall, nextWinding(), {
         isClosed: true,
         start: 0,
-        end: polygonSmall.length,
+        end: flatPolygonSmall.length,
         size: 2
       });
     })
-    .add('Polygon#modifyWindingDirection() M', () => {
-      const polygon = new Polygon(polygonMedium);
+    .add('Polygon#modifyWindingDirection() flat medium', () => {
+      const polygon = new Polygon(flatPolygonMedium);
       polygon.modifyWindingDirection(nextWinding());
     })
-    .add('modifyPolygonWindingDirection() M', () => {
-      modifyPolygonWindingDirection(polygonMedium, nextWinding(), {
+    .add('modifyPolygonWindingDirection() flat medium', () => {
+      modifyPolygonWindingDirection(flatPolygonMedium, nextWinding(), {
         isClosed: true,
         start: 0,
-        end: polygonMedium.length,
+        end: flatPolygonMedium.length,
         size: 2
       });
     })
-    .add('Polygon#getSignedArea()', () => {
-      const polygon = new Polygon(polygonMedium);
+    .add('Polygon#getSignedArea() flat medium', () => {
+      const polygon = new Polygon(flatPolygonMedium);
       polygon.getSignedArea();
     })
-    .add('Polygon#getSignedArea() nested', () => {
-      const polygon = new Polygon(polygonMediumNested);
+    .add('Polygon#getSignedArea(fast) flat medium', () => {
+      const polygon = new Polygon(flatPolygonMedium);
+      polygon.getSignedArea(true);
+    })
+    .add('Polygon#getSignedArea() nested medium', () => {
+      const polygon = new Polygon(nestedPolygonMedium);
+      polygon.getSignedArea();
+    })
+    .add('Polygon#getSignedArea(fast) nested medium', () => {
+      const polygon = new Polygon(nestedPolygonMedium);
+      polygon.getSignedArea(true);
+    })
+    .add('Polygon#getSignedArea() flat large', () => {
+      const polygon = new Polygon(flatPolygonLarge);
       polygon.getSignedArea();
     })
-    .add('earcut with precomputed areas ', () => {
-      earcut(polygonMedium, [], 2, [-21.3664]);
+    .add('Polygon#getSignedArea(fast) flat large ', () => {
+      const polygon = new Polygon(flatPolygonLarge);
+      polygon.getSignedArea(true);
+    })
+    .add('Polygon#getSignedArea() nested large', () => {
+      const polygon = new Polygon(nestedPolygonLarge);
+      polygon.getSignedArea();
+    })
+    .add('Polygon#getSignedArea(fast) nested large', () => {
+      const polygon = new Polygon(nestedPolygonLarge);
+      polygon.getSignedArea(true);
+    })
+    .add('earcut with precomputed areas', () => {
+      earcut(flatPolygonMedium, [], 2, [-21.3664]);
     })
     .add('earcut', () => {
-      earcut(polygonMedium, [], 2);
+      earcut(flatPolygonMedium, [], 2);
     });
 
   return suite;

test/bench/modules.bench.ts

@@ -9,9 +9,9 @@ import {cullingBench} from '../../modules/culling/test/bench';
 import {polygonBench} from '../../modules/polygon/test/bench';
 
 export default function addBenchmarks(suite: Bench, addReferenceBenchmarks: boolean): Bench {
-  coreBench(suite, addReferenceBenchmarks);
-  geospatialBench(suite, addReferenceBenchmarks);
-  cullingBench(suite, addReferenceBenchmarks);
+  // coreBench(suite, addReferenceBenchmarks);
+  // geospatialBench(suite, addReferenceBenchmarks);
+  // cullingBench(suite, addReferenceBenchmarks);
   polygonBench(suite, addReferenceBenchmarks);
 
   return suite;