fix: repair collision detection

Signed-off-by: André Jaenisch <andre.jaenisch@posteo.de>

src/js/app.js

@@ -1,4 +1,4 @@
-import { testBoundaries, testCollision } from './collisions.js'
+import { testCollision } from './collisions.js'
 import { drawShape } from './draw.js'
 import { makeAstronaut, makeBottomBoundary } from './world.js'
 
@@ -54,14 +54,8 @@ function tick () {
   drawShape(context, bottomBoundary)
   drawShape(context, astronaut)
 
-  if (testBoundaries(bottomBoundary, astronaut)) {
-    if (testCollision(bottomBoundary, astronaut)) {
-      throw new Error('Game Over!')
-    }
-  }
-
-  if (astronaut.C.y - astronaut.H > canvas.height) {
-    throw new Error('Should have been caught earlier!')
+  if (testCollision(bottomBoundary, astronaut)) {
+    throw new Error('Game Over!')
   }
 
   window.requestAnimationFrame(tick)

src/js/collisions.js

@@ -31,7 +31,6 @@ export function testCollision (shape1, shape2) {
         const vertices = [...vertex1, ...vertex2]
 
         if (testIntersection(vertices)) {
-          console.debug(shape1, shape2, vertices)
           throw new Error('Intersection!')
         }
       })
@@ -44,33 +43,6 @@ export function testCollision (shape1, shape2) {
   return false
 }
 
-/**
- * Computes all vertices as point-direction pairs.
- *
- * @param {Shape} shape
- * @returns {Array<Array<Vector2D>>}
- */
-function getVertices (shape) {
-  return [
-    [
-      shape.X[0],
-      subtract(shape.X[0], shape.X[1])
-    ],
-    [
-      shape.X[0],
-      subtract(shape.X[0], shape.X[3])
-    ],
-    [
-      shape.X[2],
-      subtract(shape.X[2], shape.X[1])
-    ],
-    [
-      shape.X[2],
-      subtract(shape.X[2], shape.X[3])
-    ]
-  ]
-}
-
 /**
  * Checks for intersection of two lines given by v1 and v2, resp. v3 and v4.
  *
@@ -78,15 +50,41 @@ function getVertices (shape) {
  * @returns {boolean}
  * @see {@link https://en.wikipedia.org/wiki/Line%E2%80%93line_intersection#Given_two_points_on_each_line_segment}
  */
-function testIntersection ([v1, v2, v3, v4]) {
-  const tdivident = determinant(subtract(v1, v3), subtract(v3, v4))
+export function testIntersection ([v1, v2, v3, v4]) {
   const tdivisor = determinant(subtract(v1, v2), subtract(v3, v4))
-  const t = tdivident / tdivisor
 
-  const udivident = determinant(subtract(v2, v1), subtract(v1, v3))
+  if (tdivisor === 0) {
+    // Parallel lines never intersect
+    return false
+  }
+
   const udivisor = determinant(subtract(v1, v2), subtract(v3, v4))
-  const u = udivident / udivisor
 
-  console.debug(t, u)
-  return (t <= 0 && t <= 1) || (u <= 0 && u <= 1)
+  if (udivisor === 0) {
+    // Parallel lines never intersect
+    return false
+  }
+
+  const tdivident = determinant(subtract(v1, v3), subtract(v3, v4))
+  const udivident = determinant(subtract(v2, v1), subtract(v1, v3))
+  // + 0 turns -0 into +0
+  const t = tdivident / tdivisor + 0
+  const u = udivident / udivisor + 0
+
+  return (t >= 0 && t <= 1) && (u >= 0 && u <= 1)
+}
+
+/**
+ * Computes all vertices as point-direction pairs.
+ *
+ * @param {Shape} shape
+ * @returns {Array<Array<Vector2D>>}
+ */
+function getVertices (shape) {
+  return shape.X.map(function (vertex, index) {
+    return [
+      vertex,
+      shape.X[(index + 1) % 4]
+    ]
+  })
 }

test/js/collisions.test.js

@@ -1,6 +1,10 @@
 import { expect } from 'chai'
 
-import { testBoundaries, testCollision } from '../../src/js/collisions.js'
+import {
+  testBoundaries,
+  testCollision,
+  testIntersection
+} from '../../src/js/collisions.js'
 import { RigidShape } from '../../src/js/shape.js'
 import { Vec2 } from '../../src/js/vector.js'
 
@@ -19,6 +23,22 @@ describe('Collisions', function () {
     })
   })
 
+  describe('testIntersection', function () {
+    it('should test for intersecting line segments', function () {
+      // Arrange
+      const v1 = Vec2(97.5, 97.5)
+      const v2 = Vec2(-5, 0)
+      const v3 = Vec2(94.5, 97.5)
+      const v4 = Vec2(0, -5)
+
+      // Act
+      const haveIntersectingLineSegments = testIntersection([v1, v2, v3, v4])
+
+      // Assert
+      expect(haveIntersectingLineSegments).to.equal(true)
+    })
+  })
+
   describe('testCollision', function () {
     it('should test in depth for collisions', function () {
       // Arrange
@@ -31,11 +51,35 @@ describe('Collisions', function () {
       // Assert
       expect(haveCollided).to.equal(true)
     })
+
+    it('should test for no contact', function () {
+      // Arrange
+      const shape1 = makeShape({ centre: Vec2(100, 100) })
+      const shape2 = makeShape({ centre: Vec2(94, 100) })
+
+      // Act
+      const haveCollided = testCollision(shape1, shape2)
+
+      // Assert
+      expect(haveCollided).to.equal(false)
+    })
+
+    it('should test for direct contact', function () {
+      // Arrange
+      const shape1 = makeShape({ centre: Vec2(100, 100) })
+      const shape2 = makeShape({ centre: Vec2(95, 100) })
+
+      // Act
+      const haveCollided = testCollision(shape1, shape2)
+
+      // Assert
+      expect(haveCollided).to.equal(true)
+    })
   })
 })
 
-function makeShape () {
-  const center = Vec2(500, 200)
+function makeShape ({ centre } = {}) {
+  const center = centre || Vec2(500, 200)
   const friction = 20
   const restitution = 0
   const mass = 400

types/collisions.d.ts

@@ -16,5 +16,13 @@ export function testBoundaries(shape1: Shape, shape2: Shape): boolean;
  * @returns {boolean}
  */
 export function testCollision(shape1: Shape, shape2: Shape): boolean;
+/**
+ * Checks for intersection of two lines given by v1 and v2, resp. v3 and v4.
+ *
+ * @param {Array<Vector2D>} vertices
+ * @returns {boolean}
+ * @see {@link https://en.wikipedia.org/wiki/Line%E2%80%93line_intersection#Given_two_points_on_each_line_segment}
+ */
+export function testIntersection([v1, v2, v3, v4]: Array<Vector2D>): boolean;
 export type Shape = import('./shape').Shape;
 export type Vector2D = import('./vector').Vector2D;