Fix Polygon collision when shapes are equal (#196)

Author: joshestein

src/point.ts

@@ -8,7 +8,6 @@ import {total} from '@mathigon/core';
 import {clamp, lerp, nearlyEquals, Random, roundTo, square} from '@mathigon/fermat';
 import {Bounds} from './bounds';
 import {Line} from './line';
-import {isPoint} from './types';
 import {GeoElement, rad, SimplePoint, TransformMatrix} from './utilities';
 
 

src/polygon.ts

@@ -3,7 +3,6 @@
 // (c) Mathigon
 // =============================================================================
 
-
 import {last, tabulate} from '@mathigon/core';
 import {nearlyEquals} from '@mathigon/fermat';
 import {Circle} from './circle';
@@ -12,7 +11,6 @@ import {Line, Segment} from './line';
 import {ORIGIN, Point} from './point';
 import {findClosest, GeoShape, SimplePoint, TransformMatrix, TWO_PI} from './utilities';
 
-
 /** A polygon defined by its vertex points. */
 export class Polygon implements GeoShape {
   readonly type: string = 'polygon';
@@ -88,7 +86,7 @@ export class Polygon implements GeoShape {
   }
 
   /** Checks if two polygons p1 and p2 collide. */
-  static collision(p1: Polygon, p2: Polygon) {
+  static collision(p1: Polygon, p2: Polygon, tolerance?: number) {
     // Check if one of the vertices is in one of the polygons.
     if (p1.points.some(q => p2.contains(q))) return true;
     if (p2.points.some(q => p1.contains(q))) return true;
@@ -100,7 +98,7 @@ export class Polygon implements GeoShape {
       }
     }
 
-    return false;
+    return p1.equals(p2, tolerance);
   }
 
   /** Creates a regular polygon. */

src/rectangle.ts

@@ -79,7 +79,7 @@ export class Rectangle implements GeoShape {
 
   collision(r: Rectangle) {
     return (this.p.x < r.p.x + r.w && this.p.x + this.w > r.p.x &&
-            this.p.y < r.p.y + r.h && this.p.y + this.h > r.p.y);
+      this.p.y < r.p.y + r.h && this.p.y + this.h > r.p.y) || this.equals(r.polygon);
   }
 
   padding(top: number, right: number, bottom: number, left: number) {
@@ -150,9 +150,8 @@ export class Rectangle implements GeoShape {
     return this.shift(p.x, p.y);
   }
 
-  equals(_other: Polygon) {
-    // TODO Implement
-    return false;
+  equals(other: Polygon) {
+    return this.polygon.equals(other);
   }
 
   toString() {

test/polygon-test.ts

@@ -3,13 +3,10 @@
 // (c) Mathigon
 // =============================================================================
 
-
 import tape from 'tape';
-import {Line, Point, Polygon, Polyline} from '../src';
-
-
-const poly = (...p: number[][]) => new Polygon(...p.map(q => new Point(q[0], q[1])));
+import {Point, Polygon, Polyline, Rectangle} from '../src';
 
+const poly = (...p: number[][]) => new Polygon(...p.map((q) => new Point(q[0], q[1])));
 
 tape('Length and Circumference', (test) => {
   const p1 = poly([0, 0], [0, 1], [1, 1], [1, 0]);
@@ -32,3 +29,11 @@ tape('Convex Hull', (test) => {
 
   test.end();
 });
+
+tape('Collision and Equals', (test) => {
+  const rect = new Rectangle(new Point(0, 0), 1);
+  const shape = poly([0, 0], [0, 1], [1, 1], [1, 0]);
+  test.equal(Polygon.collision(rect.polygon, shape), true);
+  test.equal(rect.equals(shape), true);
+  test.end();
+});