Do dat math!

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@3612 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/jme/sprite/BallisticPath.java

@@ -21,6 +21,7 @@
 
 package com.threerings.jme.sprite;
 
+import com.jme.math.FastMath;
 import com.jme.math.Vector3f;
 
 /**
@@ -62,6 +63,26 @@ public class BallisticPath extends Path
         }
     }
 
+    /**
+     * Computes and returns the angle of elevation needed to launch a
+     * ballistic projectile at the specified velocity and have it travel
+     * the specified range (when it will once again reach the launch
+     * elevation).
+     */
+    public static float computeElevation (float range, float vel, float accel)
+    {
+        return FastMath.asin(accel * range / (vel * vel)) / 2;
+    }
+
+    /**
+     * Computes and returns the flight time of a projectile launched at an
+     * angle previously computed with {@link #computeElevation}..
+     */
+    public static float computeFlightTime (float range, float vel, float angle)
+    {
+        return range / (vel * FastMath.cos(angle));
+    }
+
     protected Vector3f _curpos, _velocity, _accel;
     protected float _duration, _accum;
     protected Vector3f _temp = new Vector3f(0, 0, 0);