Created a specialization of the ballistic path that orients the sprite in

the direction of motion as it traverses the path.


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@3614 542714f4-19e9-0310-aa3c-eee0fc999fb1

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

@@ -0,0 +1,86 @@
+//
+// $Id$
+//
+// Narya library - tools for developing networked games
+// Copyright (C) 2002-2005 Three Rings Design, Inc., All Rights Reserved
+// http://www.threerings.net/code/narya/
+//
+// This library is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License as published
+// by the Free Software Foundation; either version 2.1 of the License, or
+// (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+package com.threerings.jme.sprite;
+
+import com.jme.math.FastMath;
+import com.jme.math.Matrix3f;
+import com.jme.math.Quaternion;
+import com.jme.math.Vector3f;
+
+/**
+ * A ballistic path that orients the sprite toward the velocity vector as
+ * it traverses the path.
+ */
+public class OrientingBallisticPath extends BallisticPath
+{
+    /**
+     * Creates a {@link BallisticPath} that will rotate the sprite so that
+     * the supplied <code>orient</code> is aligned with the velocity
+     * vector at all points along the path. If the provided orientation is
+     * not initially in line with the starting velocity, the sprite will
+     * be rotated immediately and then adjusted as it follows the path.
+     */
+    public OrientingBallisticPath (
+        Sprite sprite, Vector3f orient, Vector3f start, Vector3f velocity,
+        Vector3f accel, float duration)
+    {
+        super(sprite, start, velocity, accel, duration);
+
+        // rotate the sprite to start
+        rotate(orient, velocity);
+    }
+
+    // documentation inherited
+    public void update (float time)
+    {
+        // keep track of the old velocity before we update
+        _ovelocity.set(_velocity);
+
+        // do the normal update
+        super.update(time);
+
+        // rotate the sprite accordingly
+        rotate(_ovelocity, _velocity);
+    }
+
+    protected void rotate (Vector3f oorient, Vector3f norient)
+    {
+        // compute the cross product to get the normal to the plane
+        // defined by the velocity vectors
+        oorient.cross(norient, _normal);
+
+        // compute the angle between the two vectors
+        float angle = FastMath.acos(
+            oorient.dot(norient) / (norient.length() * oorient.length()));
+
+        // now use that to compute a rotation matrix from the old to the
+        // new vector
+        _rotate.fromAngleAxis(angle, _normal);
+
+        // finally rotate the sprite accordingly
+        _sprite.getLocalRotation().multLocal(_rotate);
+    }
+
+    protected Vector3f _ovelocity = new Vector3f();
+    protected Vector3f _normal = new Vector3f();
+    protected Quaternion _rotate = new Quaternion();
+}

tests/src/java/com/threerings/jme/sprite/PathTest.java

@@ -24,8 +24,10 @@ public class PathTest extends JmeApp
     {
         super.initRoot();
 
+        float range = 56, muzvel = 24;
+
         // set up the camera
-        Vector3f loc = new Vector3f(250, -600, 0);
+        Vector3f loc = new Vector3f(range/2, -range*2, 0);
         _camera.setLocation(loc);
         Matrix3f rotm = new Matrix3f();
         rotm.fromAngleAxis(-FastMath.PI/2, _camera.getLeft());
@@ -34,8 +36,6 @@ public class PathTest extends JmeApp
         rotm.multLocal(_camera.getLeft());
         _camera.update();
 
-        float range = 560, muzvel = 82;
-
         Box box = new Box("box", new Vector3f(-1, -1, -1),
                           new Vector3f(1, 1, 1));
         _geom.attachChild(box);
@@ -45,9 +45,8 @@ public class PathTest extends JmeApp
         box2.setLocalTranslation(new Vector3f(range, 0, 0));
         _geom.attachChild(box2);
 
-        Sphere ball = new Sphere("ball", 10, 10, 1);
         Sprite shot = new Sprite();
-        shot.attachChild(ball);
+        shot.attachChild(box);
         _geom.attachChild(shot);
 
         Vector3f start = new Vector3f(0, 0, 0);
@@ -65,7 +64,8 @@ public class PathTest extends JmeApp
         vel.multLocal(muzvel);
 
         float time = BallisticPath.computeFlightTime(range, muzvel, angle);
-        shot.move(new BallisticPath(shot, start, vel, GRAVITY, time));
+        shot.move(new OrientingBallisticPath(
+                      shot, new Vector3f(1, 0, 0), start, vel, GRAVITY, time));
 
         System.out.println("Range: " + range);
         System.out.println("Muzzle velocity: " + muzvel);