Modified animation manager to provide a timestamp with every tick.

Modified sprite and path code to make use of these timestamps to determine
a sprite's progress along the path. Abstracted the path stuff so that
paths other than line segment paths can be cleanly implemented.


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@337 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/media/util/Path.java

@@ -0,0 +1,45 @@
+//
+// $Id: Path.java,v 1.1 2001/09/13 19:10:26 mdb Exp $
+
+package com.threerings.media.sprite;
+
+import java.awt.Graphics2D;
+
+/**
+ * A path is used to cause a sprite to follow a particular path along the
+ * screen. The sprite will call into the path every time it is ticked by
+ * the animation manager and the path is responsible for updating the
+ * position of the sprite based on the time that has elapsed since the
+ * sprite started down the path. The animation manager attempts to tick
+ * once per frame at the desired frame rate, but may tick less often if
+ * CPU resources are limited, thus paths should not rely on tick counts
+ * but instead use elapsed time to determine progress.
+ *
+ * <p> The path should call back to the sprite (via {@link
+ * Sprite#pathCompleted}) to let it know when the path has been completed.
+ */
+public interface Path
+{
+    /**
+     * Called once to let the path prepare itself for the process of
+     * animating the supplied sprite.
+     */
+    public void init (Sprite sprite, long timestamp);
+
+    /**
+     * Called to request that this path update the position of the
+     * specified sprite based on the supplied timestamp information. A
+     * path should record its initial timestamp and determine the progress
+     * of the sprite along the path based on the time elapsed since the
+     * sprite began down the path.
+     *
+     * @return true if the sprite's position was updated, false if the
+     * path determined that the sprite should not move at this time.
+     */
+    public boolean updatePosition (Sprite sprite, long timestamp);
+
+    /**
+     * Paint this path on the screen (used for debugging purposes only).
+     */
+    public void paint (Graphics2D gfx);
+}