Introduce rotation methods to the Vector class

By: Bjarne Koll <LynxPlay101@gmail.com>

paper-api/src/test/java/org/bukkit/util/VectorTest.java

@@ -0,0 +1,117 @@
+package org.bukkit.util;
+
+import org.bukkit.block.BlockFace;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class VectorTest {
+
+    @Test
+    public void testNormalisedVectors() {
+        assertFalse(new Vector(1, 0, 0).multiply(1.1).isNormalized());
+
+        assertTrue(new Vector(1, 1, 1).normalize().isNormalized());
+        assertTrue(new Vector(1, 0, 0).isNormalized());
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testNullVectorAxis() {
+        new Vector(0, 1, 0).rotateAroundAxis(null, Math.PI);
+    }
+
+    @Test
+    public void testBypassingAxisVector() {
+        new Vector(0, 1, 0).rotateAroundNonUnitAxis(new Vector(1, 1, 1), Math.PI); // This will result some weird result, but there may be some use for it for some people
+    }
+
+    @Test
+    public void testResizeAxis() {
+        Vector axis = new Vector(0, 10, 0);
+        assertEquals(BlockFace.EAST.getDirection().rotateAroundAxis(axis, Math.PI * 0.5), BlockFace.NORTH.getDirection());
+    }
+
+    /**
+     * As west to east are the x axis in Minecraft, rotating around it from up
+     * should lead to up -> south -> down -> north.
+     */
+    @Test
+    public void testRotationAroundX() {
+        Vector vector = BlockFace.UP.getDirection();
+        assertEquals(BlockFace.SOUTH.getDirection(), vector.clone().rotateAroundX(Math.PI * 0.5)); // Should rotate around x axis for 1/4 of a circle.
+        assertEquals(BlockFace.DOWN.getDirection(), vector.clone().rotateAroundX(Math.PI * 1.0)); // Should rotate around x axis for 2/4 of a circle.
+        assertEquals(BlockFace.NORTH.getDirection(), vector.clone().rotateAroundX(Math.PI * 1.5)); // Should rotate around x axis for 3/4 of a circle.
+        assertEquals(BlockFace.UP.getDirection(), vector.clone().rotateAroundX(Math.PI * 2.0)); // Should rotate around x axis for 4/4 of a circle.
+    }
+
+    /**
+     * As up to down are the y axis in Minecraft, rotating around it from up
+     * should lead to east (positive x) -> south -> west -> north.
+     */
+    @Test
+    public void testRotationAroundY() {
+        Vector vector = BlockFace.EAST.getDirection();
+        assertEquals(BlockFace.NORTH.getDirection(), vector.clone().rotateAroundY(Math.PI * 0.5)); // Should rotate around x axis for 1/4 of a circle.
+        assertEquals(BlockFace.WEST.getDirection(), vector.clone().rotateAroundY(Math.PI * 1.0)); // Should rotate around x axis for 2/4 of a circle.
+        assertEquals(BlockFace.SOUTH.getDirection(), vector.clone().rotateAroundY(Math.PI * 1.5)); // Should rotate around x axis for 3/4 of a circle.
+        assertEquals(BlockFace.EAST.getDirection(), vector.clone().rotateAroundY(Math.PI * 2.0)); // Should rotate around x axis for 4/4 of a circle.
+    }
+
+    /**
+     * As up to down are the y axis in Minecraft, rotating around it from up
+     * should lead to east (positive x) -> south -> west -> north.
+     */
+    @Test
+    public void testRotationAroundYUsingCustomAxis() {
+        Vector vector = BlockFace.EAST.getDirection();
+        Vector axis = BlockFace.UP.getDirection();
+        assertEquals(BlockFace.NORTH.getDirection(), vector.clone().rotateAroundAxis(axis, Math.PI * 0.5)); // Should rotate around x axis for 1/4 of a circle.
+        assertEquals(BlockFace.WEST.getDirection(), vector.clone().rotateAroundAxis(axis, Math.PI * 1.0)); // Should rotate around x axis for 2/4 of a circle.
+        assertEquals(BlockFace.SOUTH.getDirection(), vector.clone().rotateAroundAxis(axis, Math.PI * 1.5)); // Should rotate around x axis for 3/4 of a circle.
+        assertEquals(BlockFace.EAST.getDirection(), vector.clone().rotateAroundAxis(axis, Math.PI * 2.0)); // Should rotate around x axis for 4/4 of a circle.
+    }
+
+    /**
+     * As south to north are the z axis in Minecraft, rotating around it from up
+     * should lead to up (positive y) -> west -> down -> east.
+     */
+    @Test
+    public void testRotationAroundZ() {
+        Vector vector = BlockFace.UP.getDirection();
+        assertEquals(BlockFace.WEST.getDirection(), vector.clone().rotateAroundZ(Math.PI * 0.5)); // Should rotate around x axis for 1/4 of a circle.
+        assertEquals(BlockFace.DOWN.getDirection(), vector.clone().rotateAroundZ(Math.PI * 1.0)); // Should rotate around x axis for 2/4 of a circle.
+        assertEquals(BlockFace.EAST.getDirection(), vector.clone().rotateAroundZ(Math.PI * 1.5)); // Should rotate around x axis for 3/4 of a circle.
+        assertEquals(BlockFace.UP.getDirection(), vector.clone().rotateAroundZ(Math.PI * 2.0)); // Should rotate around x axis for 4/4 of a circle.
+    }
+
+    @Test
+    public void testRotationAroundAxis() {
+        Vector axis = new Vector(1, 0, 1);
+        assertEquals(new Vector(0, 1, 0).rotateAroundNonUnitAxis(axis, Math.PI * 0.5), new Vector(-1, 0, 1));
+    }
+
+    @Test
+    public void testRotationAroundAxisNonUnit() {
+        Vector axis = new Vector(0, 2, 0);
+        Vector v = BlockFace.EAST.getDirection();
+
+        assertEquals(v.rotateAroundNonUnitAxis(axis, Math.PI * 0.5), BlockFace.NORTH.getDirection().multiply(2));
+    }
+
+    /**
+     * This will be a bit tricky to prove so we will try to simply see if the
+     * vectors have correct angle to each other This will work with any two
+     * vectors, as the rotation will keep the angle the same.
+     */
+    @Test
+    public void testRotationAroundCustomAngle() {
+        Vector axis = new Vector(-30, 1, 2000).normalize();
+        Vector v = new Vector(53, 12, 98);
+
+        float a = v.angle(axis);
+        double stepSize = Math.PI / 21;
+        for (int i = 0; i < 42; i++) {
+            v.rotateAroundAxis(axis, stepSize);
+            assertEquals(a, v.angle(axis), Vector.getEpsilon());
+        }
+    }
+}