From f26a72c26f58b902b5db8484297bc710d219e4ed Mon Sep 17 00:00:00 2001
From: Michael Bayne <mdb@samskivert.com>
Date: Tue, 12 Feb 2013 14:24:04 -0800
Subject: [PATCH] Change new mirrorAngle to mirrorAngleOrigin, improved
 javadocs.

The old mirrorAngle mirrors around the "y-axis" (PI/2 or -PI/2 as appropriate)
which is necessary for other code (particularly angularDifference) to work
correctly. The new mirrorAngleOrigin mirrors around the "x-axis" (zero).
---
 src/main/java/pythagoras/f/MathUtil.java     | 13 +++++++++-
 src/test/java/pythagoras/f/MathUtilTest.java | 25 +++++++++++++++++---
 2 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/src/main/java/pythagoras/f/MathUtil.java b/src/main/java/pythagoras/f/MathUtil.java
index 133df38..37ca460 100644
--- a/src/main/java/pythagoras/f/MathUtil.java
+++ b/src/main/java/pythagoras/f/MathUtil.java
@@ -166,9 +166,20 @@ public class MathUtil
     }
 
     /**
-     * Returns the mirror angle of the specified angle (assumed to be in [-pi, +pi]).
+     * Returns the mirror angle of the specified angle (assumed to be in [-pi, +pi]). The angle is
+     * mirrored around the PI/2 if it is positive, and -PI/2 if it is negative. One can visualize
+     * this as mirroring around the "y-axis".
      */
     public static float mirrorAngle (float a) {
+        return (a > 0f ? FloatMath.PI : -FloatMath.PI) - a;
+    }
+
+    /**
+     * Returns the mirror angle of the specified angle (assumed to be in [-pi, +pi]). The angle is
+     * mirrored around the origin (zero degrees). One can visualize this as mirroring around the
+     * "x-axis".
+     */
+    public static float mirrorAngleOrigin (float a) {
         return a + (a > 0f ? -FloatMath.PI : FloatMath.PI);
     }
 
diff --git a/src/test/java/pythagoras/f/MathUtilTest.java b/src/test/java/pythagoras/f/MathUtilTest.java
index 5111d8a..569e76f 100644
--- a/src/test/java/pythagoras/f/MathUtilTest.java
+++ b/src/test/java/pythagoras/f/MathUtilTest.java
@@ -12,8 +12,27 @@ import static org.junit.Assert.*;
  */
 public class MathUtilTest
 {
-    @Test public void testMirrorAngle() {
-        assertEquals(-MathUtil.HALF_PI, MathUtil.mirrorAngle(MathUtil.HALF_PI), MathUtil.EPSILON);
-        assertEquals(MathUtil.HALF_PI, MathUtil.mirrorAngle(-MathUtil.HALF_PI), MathUtil.EPSILON);
+    public static final float PI = FloatMath.PI;
+    public static final float PI2 = FloatMath.PI/2;
+    public static final float PI4 = FloatMath.PI/4;
+    public static final float PI8 = FloatMath.PI/8;
+
+    @Test public void testLerpa() {
+        assertEquals(MathUtil.lerpa(PI4, -PI4, 0.25f), PI8, MathUtil.EPSILON);
+        assertEquals(MathUtil.lerpa(PI4, -PI4, 0.75f), -PI8, MathUtil.EPSILON);
+        assertEquals(MathUtil.lerpa(-PI4, PI4, 0.25f), -PI8, MathUtil.EPSILON);
+        assertEquals(MathUtil.lerpa(-PI4, PI4, 0.75f), PI8, MathUtil.EPSILON);
+        // make sure we lerp the shortest route around the circle
+        assertEquals(MathUtil.lerpa(3*PI4, PI4, 0.5f), PI2, MathUtil.EPSILON);
+        assertEquals(MathUtil.lerpa(PI4, 3*PI4, 0.5f), PI2, MathUtil.EPSILON);
+        assertEquals(MathUtil.lerpa(-3*PI4, -PI4, 0.5f), -PI2, MathUtil.EPSILON);
+        assertEquals(MathUtil.lerpa(-PI4, -3*PI4, 0.5f), -PI2, MathUtil.EPSILON);
+
+        assertEquals(MathUtil.lerpa(3*PI4, -3*PI4, 0.5f), -PI, MathUtil.EPSILON);
+    }
+
+    @Test public void testMirrorAngleOrigin() {
+        assertEquals(-PI2, MathUtil.mirrorAngleOrigin(PI2), MathUtil.EPSILON);
+        assertEquals(PI2, MathUtil.mirrorAngleOrigin(-PI2), MathUtil.EPSILON);
     }
 }