Created an mechanism for more sophisticated sequencing of animation

frames.


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@1695 542714f4-19e9-0310-aa3c-eee0fc999fb1

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

@@ -0,0 +1,96 @@
+//
+// $Id: FrameSequencer.java,v 1.1 2002/09/17 20:07:28 mdb Exp $
+
+package com.threerings.media.util;
+
+import com.threerings.media.util.MultiFrameImage;
+
+/**
+ * Used to control animation timing when displaying a {@link
+ * MultiFrameImage}. This interface allows for constant framerates, or
+ * more sophisticated animation timing.
+ */
+public interface FrameSequencer
+{
+    /**
+     * Called prior to the execution of an animation sequence (not
+     * necessarily immediately, so time stamps should be obtained in the
+     * first call to tick).
+     *
+     * @param source the multie-frame image that is providing the
+     * animation frames.
+     */
+    public void init (MultiFrameImage source);
+
+    /**
+     * Called every display frame, the frame sequencer should return the
+     * index of the animation frame that should be displayed during this
+     * tick. If the sequencer returns -1, it is taken as an indication
+     * that the animation is finished and should be stopped.
+     */
+    public int tick (long tickStamp);
+
+    /**
+     * Called if the display is paused for some length of time and then
+     * unpaused. Sequencers should adjust any time stamps they are
+     * maintaining internally by the delta so that time maintains the
+     * illusion of flowing smoothly forward.
+     */
+    public void fastForward (long timeDelta);
+
+    /**
+     * A frame sequencer that delivers a constant frame rate in either one
+     * shot or looping mode.
+     */
+    public static class ConstantRate implements FrameSequencer
+    {
+        /**
+         * Creates a constant rate frame sequencer with the desired target
+         * frames per second.
+         *
+         * @param framesPerSecond the target frames per second.
+         * @param loop if false, the sequencer will report the end of
+         * the animation after progressing through all of the frames once,
+         * otherwise it will loop indefinitely.
+         */
+        public ConstantRate (double framesPerSecond, boolean loop)
+        {
+            _millisPerFrame = (long)(1000d / _millisPerFrame);
+            _loop = loop;
+        }
+
+        // documentation inherited from interface
+        public void init (MultiFrameImage source)
+        {
+            _frameCount = source.getFrameCount();
+            _startStamp = 0l;
+        }
+
+        // documentation inherited from interface
+        public int tick (long tickStamp)
+        {
+            // obtain our starting timestamp if we don't already have one
+            if (_startStamp == 0) {
+                _startStamp = tickStamp;
+            }
+
+            // compute our current frame index
+            int frameIdx = (int)((tickStamp - _startStamp) / _millisPerFrame);
+
+            // if we're not looping and we've exhausted our frames, we
+            // return -1 to indicate that the animation should stop
+            return (!_loop && frameIdx >= _frameCount) ? -1 : frameIdx;
+        }
+
+        // documentation inherited from interface
+        public void fastForward (long timeDelta)
+        {
+            _startStamp += timeDelta;
+        }
+
+        protected long _millisPerFrame;
+        protected boolean _loop;
+        protected int _frameCount;
+        protected long _startStamp;
+    }
+}