Adding ElasticCollision2D (#6802)

* Adding ElasticCollision2D * Fixing build issues.
2025-12-19 07:00:35 +08:00 · 2025-10-19 22:30:32 +05:30
parent b312567dc3
commit a7f0bab021
2 changed files with 164 additions and 0 deletions
--- a/src/test/java/com/thealgorithms/physics/ElasticCollision2DTest.java
+++ b/src/test/java/com/thealgorithms/physics/ElasticCollision2DTest.java
@@ -0,0 +1,91 @@
+package com.thealgorithms.physics;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+class ElasticCollision2DTest {
+
+    @Test
+    void testEqualMassHeadOnCollision() {
+        ElasticCollision2D.Body a = new ElasticCollision2D.Body(0, 0, 1, 0, 1.0, 0.5);
+        ElasticCollision2D.Body b = new ElasticCollision2D.Body(1, 0, -1, 0, 1.0, 0.5);
+
+        ElasticCollision2D.resolveCollision(a, b);
+
+        assertEquals(-1.0, a.vx, 1e-6);
+        assertEquals(0.0, a.vy, 1e-6);
+        assertEquals(1.0, b.vx, 1e-6);
+        assertEquals(0.0, b.vy, 1e-6);
+    }
+
+    @Test
+    void testUnequalMassHeadOnCollision() {
+        ElasticCollision2D.Body a = new ElasticCollision2D.Body(0, 0, 2, 0, 2.0, 0.5);
+        ElasticCollision2D.Body b = new ElasticCollision2D.Body(1, 0, -1, 0, 1.0, 0.5);
+
+        ElasticCollision2D.resolveCollision(a, b);
+
+        // 1D head-on collision results
+        assertEquals(0.0, a.vx, 1e-6);
+        assertEquals(0.0, a.vy, 1e-6);
+        assertEquals(3.0, b.vx, 1e-6);
+        assertEquals(0.0, b.vy, 1e-6);
+    }
+
+    @Test
+    void testMovingApartNoCollision() {
+        ElasticCollision2D.Body a = new ElasticCollision2D.Body(0, 0, -1, 0, 1.0, 0.5);
+        ElasticCollision2D.Body b = new ElasticCollision2D.Body(1, 0, 1, 0, 1.0, 0.5);
+
+        ElasticCollision2D.resolveCollision(a, b);
+
+        assertEquals(-1.0, a.vx, 1e-6);
+        assertEquals(0.0, a.vy, 1e-6);
+        assertEquals(1.0, b.vx, 1e-6);
+        assertEquals(0.0, b.vy, 1e-6);
+    }
+
+    @Test
+    void testGlancingCollision() {
+        ElasticCollision2D.Body a = new ElasticCollision2D.Body(0, 0, 1, 1, 1.0, 0.5);
+        ElasticCollision2D.Body b = new ElasticCollision2D.Body(1, 1, -1, -0.5, 1.0, 0.5);
+
+        ElasticCollision2D.resolveCollision(a, b);
+
+        // Ensure relative velocity along normal is reversed
+        double nx = (b.x - a.x) / Math.hypot(b.x - a.x, b.y - a.y);
+        double ny = (b.y - a.y) / Math.hypot(b.x - a.x, b.y - a.y);
+        double relVelAfter = (b.vx - a.vx) * nx + (b.vy - a.vy) * ny;
+
+        assertTrue(relVelAfter > 0);
+    }
+
+    @Test
+    void testOverlappingBodies() {
+        ElasticCollision2D.Body a = new ElasticCollision2D.Body(0, 0, 1, 0, 1.0, 0.5);
+        ElasticCollision2D.Body b = new ElasticCollision2D.Body(0, 0, -1, 0, 1.0, 0.5);
+
+        ElasticCollision2D.resolveCollision(a, b);
+
+        // Should not crash, velocities may remain unchanged
+        assertEquals(1.0, a.vx, 1e-6);
+        assertEquals(0.0, a.vy, 1e-6);
+        assertEquals(-1.0, b.vx, 1e-6);
+        assertEquals(0.0, b.vy, 1e-6);
+    }
+
+    @Test
+    void testStationaryBodyHit() {
+        ElasticCollision2D.Body a = new ElasticCollision2D.Body(0, 0, 2, 0, 1.0, 0.5);
+        ElasticCollision2D.Body b = new ElasticCollision2D.Body(1, 0, 0, 0, 1.0, 0.5);
+
+        ElasticCollision2D.resolveCollision(a, b);
+
+        assertEquals(0.0, a.vx, 1e-6);
+        assertEquals(0.0, a.vy, 1e-6);
+        assertEquals(2.0, b.vx, 1e-6);
+        assertEquals(0.0, b.vy, 1e-6);
+    }
+}