Add Location.setDirection(Vector). Adds BUKKIT-4862

This commit adds an additional method to Location to set the direction of
facing. Included are a set of unit tests that ensure the consistency of
getDirection and setDirection using a set of cardinal directions and
arbituary data points.

Javadocs were also added to pitch and yaw methods that explain the unit
and points of origin.

2 files changed, 277 insertions, 14 deletions

diff --git a/src/main/java/org/bukkit/Location.java b/src/main/java/org/bukkit/Location.java
index e3f362fd..0f74f6d4 100644
--- a/src/main/java/org/bukkit/Location.java
+++ b/src/main/java/org/bukkit/Location.java
@@ -167,45 +167,79 @@ public class Location implements Cloneable {
     }
 
     /**
-     * Sets the yaw of this location
-     *
-     * @param yaw New yaw
+     * Sets the yaw of this location, measured in degrees.
+     * <ul>
+     * <li>A yaw of 0 or 360 represents the positive z direction.
+     * <li>A yaw of 180 represents the negative z direction.
+     * <li>A yaw of 90 represents the negative x direction.
+     * <li>A yaw of 270 represents the positive x direction.
+     * </ul>
+     * Increasing yaw values are the equivalent of turning to your
+     * right-facing, increasing the scale of the next respective axis, and
+     * decreasing the scale of the previous axis.
+     *
+     * @param yaw new rotation's yaw
      */
     public void setYaw(float yaw) {
         this.yaw = yaw;
     }
 
     /**
-     * Gets the yaw of this location
+     * Gets the yaw of this location, measured in degrees.
+     * <ul>
+     * <li>A yaw of 0 or 360 represents the positive z direction.
+     * <li>A yaw of 180 represents the negative z direction.
+     * <li>A yaw of 90 represents the negative x direction.
+     * <li>A yaw of 270 represents the positive x direction.
+     * </ul>
+     * Increasing yaw values are the equivalent of turning to your
+     * right-facing, increasing the scale of the next respective axis, and
+     * decreasing the scale of the previous axis.
      *
-     * @return Yaw
+     * @return the rotation's yaw
      */
     public float getYaw() {
         return yaw;
     }
 
     /**
-     * Sets the pitch of this location
+     * Sets the pitch of this location, measured in degrees.
+     * <ul>
+     * <li>A pitch of 0 represents level forward facing.
+     * <li>A pitch of 90 represents downward facing, or negative y
+     *     direction.
+     * <li>A pitch of -90 represents upward facing, or positive y direction.
+     * <ul>
+     * Increasing pitch values the equivalent of looking down.
      *
-     * @param pitch New pitch
+     * @param pitch new incline's pitch
      */
     public void setPitch(float pitch) {
         this.pitch = pitch;
     }
 
     /**
-     * Gets the pitch of this location
+     * Sets the pitch of this location, measured in degrees.
+     * <ul>
+     * <li>A pitch of 0 represents level forward facing.
+     * <li>A pitch of 90 represents downward facing, or negative y
+     *     direction.
+     * <li>A pitch of -90 represents upward facing, or positive y direction.
+     * <ul>
+     * Increasing pitch values the equivalent of looking down.
      *
-     * @return Pitch
+     * @return the incline's pitch
      */
     public float getPitch() {
         return pitch;
     }
 
     /**
-     * Gets a Vector pointing in the direction that this Location is facing
+     * Gets a unit-vector pointing in the direction that this Location is
+     * facing.
      *
-     * @return Vector
+     * @return a vector pointing the direction of this location's {@link
+     *     #getPitch() pitch} and {@link #getYaw() yaw}
      */
     public Vector getDirection() {
         Vector vector = new Vector();
@@ -215,15 +249,48 @@ public class Location implements Cloneable {
 
         vector.setY(-Math.sin(Math.toRadians(rotY)));
 
-        double h = Math.cos(Math.toRadians(rotY));
+        double xz = Math.cos(Math.toRadians(rotY));
 
-        vector.setX(-h * Math.sin(Math.toRadians(rotX)));
-        vector.setZ(h * Math.cos(Math.toRadians(rotX)));
+        vector.setX(-xz * Math.sin(Math.toRadians(rotX)));
+        vector.setZ(xz * Math.cos(Math.toRadians(rotX)));
 
         return vector;
     }
 
     /**
+     * Sets the {@link #getYaw() yaw} and {@link #getPitch() pitch} to point
+     * in the direction of the vector.
+     */
+    public Location setDirection(Vector vector) {
+        /*
+         * Sin = Opp / Hyp
+         * Cos = Adj / Hyp
+         * Tan = Opp / Adj
+         *
+         * x = -Opp
+         * z = Adj
+         */
+        final double _2PI = 2 * Math.PI;
+        final double x = vector.getX();
+        final double z = vector.getZ();
+
+        if (x == 0 && z == 0) {
+            pitch = vector.getY() > 0 ? -90 : 90;
+            return this;
+        }
+
+        double theta = Math.atan2(-x, z);
+        yaw = (float) Math.toDegrees((theta + _2PI) % _2PI);
+
+        double x2 = NumberConversions.square(x);
+        double z2 = NumberConversions.square(z);
+        double xz = Math.sqrt(x2 + z2);
+        pitch = (float) Math.toDegrees(Math.atan(-vector.getY() / xz));
+
+        return this;
+    }
+
+    /**
      * Adds the location by another.
      *
      * @see Vector
diff --git a/src/test/java/org/bukkit/LocationTest.java b/src/test/java/org/bukkit/LocationTest.java
new file mode 100644
index 00000000..fa247763
--- /dev/null
+++ b/src/test/java/org/bukkit/LocationTest.java
@@ -0,0 +1,196 @@
+package org.bukkit;
+
+import static org.hamcrest.Matchers.*;
+import static org.junit.Assert.*;
+
+import java.util.List;
+import java.util.Random;
+
+import org.bukkit.util.Vector;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameter;
+import org.junit.runners.Parameterized.Parameters;
+
+import com.google.common.collect.ImmutableList;
+
+@RunWith(Parameterized.class)
+public class LocationTest {
+    private static final double δ = 1.0 / 1000000;
+    /**
+     * <pre>
+     * a² + b² = c², a = b
+     * => 2∙(a²) = 2∙(b²) = c², c = 1
+     * => 2∙(a²) = 1
+     * => a² = 1/2
+     * => a = √(1/2) ∎
+     * </pre>
+     */
+    private static final double HALF_UNIT = Math.sqrt(1 / 2f);
+    /**
+     * <pre>
+     * a² + b² = c², c = √(1/2)
+     * => a² + b² = √(1/2)², a = b
+     * => 2∙(a²) = 2∙(b²) = 1/2
+     * => a² = 1/4
+     * => a = √(1/4) ∎
+     * </pre>
+     */
+    private static final double HALF_HALF_UNIT = Math.sqrt(1 / 4f);
+
+    @Parameters(name= "{index}: {0}")
+    public static List<Object[]> data() {
+        Random RANDOM = new Random(1l); // Test is deterministic
+        int r = 0;
+        return ImmutableList.<Object[]>of(
+            new Object[] { "X",
+                1, 0, 0,
+                270, 0
+            },
+            new Object[] { "-X",
+                -1, 0, 0,
+                90, 0
+            },
+            new Object[] { "Z",
+                0, 0, 1,
+                0, 0
+            },
+            new Object[] { "-Z",
+                0, 0, -1,
+                180, 0
+            },
+            new Object[] { "Y",
+                0, 1, 0,
+                0, -90 // Zero is here as a "default" value
+            },
+            new Object[] { "-Y",
+                0, -1, 0,
+                0, 90 // Zero is here as a "default" value
+            },
+            new Object[] { "X Z",
+                HALF_UNIT, 0, HALF_UNIT,
+                (270 + 360) / 2, 0
+            },
+            new Object[] { "X -Z",
+                HALF_UNIT, 0, -HALF_UNIT,
+                (270 + 180) / 2, 0
+            },
+            new Object[] { "-X -Z",
+                -HALF_UNIT, 0, -HALF_UNIT,
+                (90 + 180) / 2, 0
+            },
+            new Object[] { "-X Z",
+                -HALF_UNIT, 0, HALF_UNIT,
+                (90 + 0) / 2, 0
+            },
+            new Object[] { "X Y Z",
+                HALF_HALF_UNIT, HALF_UNIT, HALF_HALF_UNIT,
+                (270 + 360) / 2, -45
+            },
+            new Object[] { "-X -Y -Z",
+                -HALF_HALF_UNIT, -HALF_UNIT, -HALF_HALF_UNIT,
+                (90 + 180) / 2, 45
+            },
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++),
+            getRandom(RANDOM, r++)
+        );
+    }
+
+    private static Object[] getRandom(Random random, int index) {
+        final double YAW_FACTOR = 360;
+        final double YAW_OFFSET = 0;
+        final double PITCH_FACTOR = 180;
+        final double PITCH_OFFSET = -90;
+        final double CARTESIAN_FACTOR = 256;
+        final double CARTESIAN_OFFSET = -128;
+
+        Vector vector;
+        Location location;
+        if (random.nextBoolean()) {
+            float pitch = (float) (random.nextDouble() * PITCH_FACTOR + PITCH_OFFSET);
+            float yaw = (float) (random.nextDouble() * YAW_FACTOR + YAW_OFFSET);
+
+            location = getEmptyLocation();
+            location.setPitch(pitch);
+            location.setYaw(yaw);
+
+            vector = location.getDirection();
+        } else {
+            double x = random.nextDouble() * CARTESIAN_FACTOR + CARTESIAN_OFFSET;
+            double y = random.nextDouble() * CARTESIAN_FACTOR + CARTESIAN_OFFSET;
+            double z = random.nextDouble() * CARTESIAN_FACTOR + CARTESIAN_OFFSET;
+
+            location = getEmptyLocation();
+            vector = new Vector(x, y, z).normalize();
+
+            location.setDirection(vector);
+        }
+
+        return new Object[] { "R" + index,
+            vector.getX(), vector.getY(), vector.getZ(),
+            location.getYaw(), location.getPitch()
+        };
+    }
+
+    @Parameter(0)
+    public String nane;
+    @Parameter(1)
+    public double x;
+    @Parameter(2)
+    public double y;
+    @Parameter(3)
+    public double z;
+    @Parameter(4)
+    public float yaw;
+    @Parameter(5)
+    public float pitch;
+
+    @Test
+    public void testExpectedPitchYaw() {
+        Location location = getEmptyLocation().setDirection(getVector());
+
+        assertThat((double) location.getYaw(), is(closeTo(yaw, δ)));
+        assertThat((double) location.getPitch(), is(closeTo(pitch, δ)));
+    }
+
+    @Test
+    public void testExpectedXYZ() {
+        Vector vector = getLocation().getDirection();
+
+        assertThat(vector.getX(), is(closeTo(x, δ)));
+        assertThat(vector.getY(), is(closeTo(y, δ)));
+        assertThat(vector.getZ(), is(closeTo(z, δ)));
+    }
+
+    private Vector getVector() {
+        return new Vector(x, y, z);
+    }
+
+    private static Location getEmptyLocation() {
+        return new Location(null, 0, 0, 0);
+    }
+
+    private Location getLocation() {
+        Location location = getEmptyLocation();
+        location.setYaw(yaw);
+        location.setPitch(pitch);
+        return location;
+    }
+}