Add a function to compute a normalized angle difference

2 files changed, 14 insertions, 1 deletions

diff --git a/main/src/cgeo/geocaching/DirectionProvider.java b/main/src/cgeo/geocaching/DirectionProvider.java
index 7bb940f..2f54b41 100644
--- a/main/src/cgeo/geocaching/DirectionProvider.java
+++ b/main/src/cgeo/geocaching/DirectionProvider.java
@@ -60,4 +60,15 @@ public class DirectionProvider extends MemorySubject<Float> implements SensorEve
         return Compatibility.getDirectionNow(direction, activity) % 360;
     }
 
+    /**
+     * Return the angle to turn of to go from an angle to the other
+     *
+     * @param from the origin angle in degrees, in the [0, 360[ range
+     * @param to the target angle in degreees, in the [0, 360[ range
+     * @return a value in degrees, in the [-180, 180[ range
+     */
+    public static double difference(final double from, final double to) {
+        return (to - from + 360 + 180) % 360 - 180;
+    }
+
 }
diff --git a/main/src/cgeo/geocaching/ui/CompassView.java b/main/src/cgeo/geocaching/ui/CompassView.java
index 6f5b8b9..56cba9d 100644
--- a/main/src/cgeo/geocaching/ui/CompassView.java
+++ b/main/src/cgeo/geocaching/ui/CompassView.java
@@ -1,5 +1,6 @@
 package cgeo.geocaching.ui;
 
+import cgeo.geocaching.DirectionProvider;
 import cgeo.geocaching.R;
 import cgeo.geocaching.utils.PeriodicHandler;
 
@@ -153,7 +154,8 @@ public class CompassView extends View {
         public void act() {
             final double newAzimuthShown = smoothUpdate(northMeasured, azimuthShown);
             final double newCacheHeadingShown = smoothUpdate(cacheHeadingMeasured, cacheHeadingShown);
-            if (Math.abs(newAzimuthShown - azimuthShown) >= 2 || Math.abs(newCacheHeadingShown - cacheHeadingShown) >= 2) {
+            if (Math.abs(DirectionProvider.difference(azimuthShown, newAzimuthShown)) >= 2 ||
+                    Math.abs(DirectionProvider.difference(cacheHeadingShown, newCacheHeadingShown)) >= 2) {
                 synchronized(CompassView.this) {
                     azimuthShown = newAzimuthShown;
                     cacheHeadingShown = newCacheHeadingShown;