Fix hit delta calculations

Author: noonat

docs/bundle.js

@@ -234,7 +234,7 @@ <h2 id="axis-aligned-bounding-boxes">Axis-Aligned Bounding Boxes</h2>
   <span class="hljs-keyword">public</span> pos: Point;
   <span class="hljs-keyword">public</span> half: Point;
 
-  <span class="hljs-keyword">constructor</span>(<span class="hljs-params">pos, half</span>) {
+  <span class="hljs-keyword">constructor</span>(<span class="hljs-params">pos: Point, half: Point</span>) {
     <span class="hljs-keyword">this</span>.pos = pos;
     <span class="hljs-keyword">this</span>.half = half;
   }</pre></div>
@@ -418,10 +418,10 @@ <h3 id="aabb-vs-segment">AABB vs Segment</h3>
       hit.normal.x = <span class="hljs-number">0</span>;
       hit.normal.y = -signY;
     }
-    hit.delta.x = hit.time * delta.x;
-    hit.delta.y = hit.time * delta.y;
-    hit.pos.x = pos.x + hit.delta.x;
-    hit.pos.y = pos.y + hit.delta.y;
+    hit.delta.x = (<span class="hljs-number">1.0</span> - hit.time) * -delta.x;
+    hit.delta.y = (<span class="hljs-number">1.0</span> - hit.time) * -delta.y;
+    hit.pos.x = pos.x + delta.x * hit.time;
+    hit.pos.y = pos.y + delta.y * hit.time;
     <span class="hljs-keyword">return</span> hit;
   }</pre></div>
 

docs/bundle.js.map

@@ -80,7 +80,7 @@ export class AABB {
   public pos: Point;
   public half: Point;
 
-  constructor(pos, half) {
+  constructor(pos: Point, half: Point) {
     this.pos = pos;
     this.half = half;
   }
@@ -144,10 +144,10 @@ export class AABB {
       hit.normal.x = 0;
       hit.normal.y = -signY;
     }
-    hit.delta.x = hit.time * delta.x;
-    hit.delta.y = hit.time * delta.y;
-    hit.pos.x = pos.x + hit.delta.x;
-    hit.pos.y = pos.y + hit.delta.y;
+    hit.delta.x = (1.0 - hit.time) * -delta.x;
+    hit.delta.y = (1.0 - hit.time) * -delta.y;
+    hit.pos.x = pos.x + delta.x * hit.time;
+    hit.pos.y = pos.y + delta.y * hit.time;
     return hit;
   }
 

index.html

@@ -209,7 +209,7 @@ each axis).
       public pos: Point;
       public half: Point;
 
-      constructor(pos, half) {
+      constructor(pos: Point, half: Point) {
         this.pos = pos;
         this.half = half;
       }
@@ -388,10 +388,10 @@ the very starting of the line, so just set the hit time to zero.
           hit.normal.x = 0;
           hit.normal.y = -signY;
         }
-        hit.delta.x = hit.time * delta.x;
-        hit.delta.y = hit.time * delta.y;
-        hit.pos.x = pos.x + hit.delta.x;
-        hit.pos.y = pos.y + hit.delta.y;
+        hit.delta.x = (1.0 - hit.time) * -delta.x;
+        hit.delta.y = (1.0 - hit.time) * -delta.y;
+        hit.pos.x = pos.x + delta.x * hit.time;
+        hit.pos.y = pos.y + delta.y * hit.time;
         return hit;
       }
 

lib/intersect.js

@@ -1,7 +1,7 @@
 import * as assert from 'assert';
 import {AABB, EPSILON, Hit, Point, Sweep} from '../src/intersect';
 
-function almostEqual(actual, expected, message) {
+function almostEqual(actual, expected, message: string = undefined) {
   if (Math.abs(actual - expected) > 1e-8) {
     assert.equal(actual, expected, message);
   }
@@ -85,8 +85,8 @@ describe('AABB', () => {
       almostEqual(hit.time, time);
       almostEqual(hit.pos.x, point.x + delta.x * time);
       almostEqual(hit.pos.y, point.y + delta.y * time);
-      almostEqual(hit.delta.x, delta.x * time);
-      almostEqual(hit.delta.y, delta.y * time);
+      almostEqual(hit.delta.x, (1.0 - time) * -delta.x);
+      almostEqual(hit.delta.y, (1.0 - time) * -delta.y);
       almostEqual(hit.normal.x, -1);
       almostEqual(hit.normal.y, 0);
     });
@@ -99,8 +99,8 @@ describe('AABB', () => {
       almostEqual(hit.time, 0);
       almostEqual(hit.pos.x, -4);
       almostEqual(hit.pos.y, 4);
-      almostEqual(hit.delta.x, 0);
-      almostEqual(hit.delta.y, 0);
+      almostEqual(hit.delta.x, -delta.x);
+      almostEqual(hit.delta.y, -delta.y);
       almostEqual(hit.normal.x, -1);
       almostEqual(hit.normal.y, 0);
     });
@@ -116,8 +116,8 @@ describe('AABB', () => {
       almostEqual(hit.time, time);
       almostEqual(hit.pos.x, point.x + delta.x * time);
       almostEqual(hit.pos.y, point.y + delta.y * time);
-      almostEqual(hit.delta.x, delta.x * time);
-      almostEqual(hit.delta.y, delta.y * time);
+      almostEqual(hit.delta.x, (1.0 - time) * -delta.x);
+      almostEqual(hit.delta.y, (1.0 - time) * -delta.y);
       almostEqual(hit.normal.x, -1);
       almostEqual(hit.normal.y, 0);
     });
@@ -296,8 +296,8 @@ describe('AABB', () => {
       almostEqual(sweep.hit.time, time);
       almostEqual(sweep.hit.pos.x, aabb2.pos.x + delta.x * time + direction.x * aabb2.half.x);
       almostEqual(sweep.hit.pos.y, aabb2.pos.y + delta.y * time + direction.y * aabb2.half.y);
-      almostEqual(sweep.hit.delta.x, delta.x * time);
-      almostEqual(sweep.hit.delta.y, delta.y * time);
+      almostEqual(sweep.hit.delta.x, (1.0 - time) * -delta.x);
+      almostEqual(sweep.hit.delta.y, (1.0 - time) * -delta.y);
     });
 
     test('should set sweep.hit.normal to normals of box 1', () => {
@@ -317,8 +317,8 @@ describe('AABB', () => {
       almostEqual(sweep.pos.x, 0);
       almostEqual(sweep.pos.y, -4);
       almostEqual(sweep.hit.time, 0);
-      almostEqual(sweep.hit.delta.x, 0);
-      almostEqual(sweep.hit.delta.y, 0);
+      almostEqual(sweep.hit.delta.x, -delta.x);
+      almostEqual(sweep.hit.delta.y, -delta.y);
     });
   });
 });