VIDEO: Add API changes to allow videos to be played backwards

2 files changed, 63 insertions, 7 deletions

diff --git a/video/video_decoder.cpp b/video/video_decoder.cpp
index ab12cfd971..ebe15c5fc1 100644
--- a/video/video_decoder.cpp
+++ b/video/video_decoder.cpp
@@ -188,6 +188,25 @@ const Graphics::Surface *VideoDecoder::decodeNextFrame() {
 	return frame;
 }
 
+bool VideoDecoder::setReverse(bool reverse) {
+	// Can only reverse video-only videos
+	if (reverse && hasAudio())
+		return false;
+
+	// Attempt to make sure all the tracks are in the requested direction
+	for (TrackList::iterator it = _tracks.begin(); it != _tracks.end(); it++) {
+		if ((*it)->getTrackType() == Track::kTrackTypeVideo && ((VideoTrack *)*it)->isReversed() != reverse) {
+			if (!((VideoTrack *)*it)->setReverse(reverse))
+				return false;
+
+			_needsUpdate = true; // force an update
+		}
+	}
+
+	findNextVideoTrack();
+	return true;
+}
+
 const byte *VideoDecoder::getPalette() {
 	_dirtyPalette = false;
 	return _palette;
@@ -218,7 +237,7 @@ uint32 VideoDecoder::getTime() const {
 		return _lastTimeChange.msecs();
 
 	if (isPaused())
-		return (_playbackRate * (_pauseStartTime - _startTime)).toInt();
+		return MAX<int>((_playbackRate * (_pauseStartTime - _startTime)).toInt(), 0);
 
 	if (useAudioSync()) {
 		for (TrackList::const_iterator it = _tracks.begin(); it != _tracks.end(); it++) {
@@ -231,20 +250,29 @@ uint32 VideoDecoder::getTime() const {
 		}
 	}
 
-	return (_playbackRate * (g_system->getMillis() - _startTime)).toInt();
+	return MAX<int>((_playbackRate * (g_system->getMillis() - _startTime)).toInt(), 0);
 }
 
 uint32 VideoDecoder::getTimeToNextFrame() const {
 	if (endOfVideo() || _needsUpdate || !_nextVideoTrack)
 		return 0;
 
-	uint32 elapsedTime = getTime();
+	uint32 currentTime = getTime();
 	uint32 nextFrameStartTime = _nextVideoTrack->getNextFrameStartTime();
 
-	if (nextFrameStartTime <= elapsedTime)
+	if (_nextVideoTrack->isReversed()) {
+		// For reversed videos, we need to handle the time difference the opposite way.
+		if (nextFrameStartTime >= currentTime)
+			return 0;
+
+		return currentTime - nextFrameStartTime;
+	}
+
+	// Otherwise, handle it normally.
+	if (nextFrameStartTime <= currentTime)
 		return 0;
 
-	return nextFrameStartTime - elapsedTime;
+	return nextFrameStartTime - currentTime;
 }
 
 bool VideoDecoder::endOfVideo() const {
@@ -402,9 +430,11 @@ void VideoDecoder::setRate(const Common::Rational &rate) {
 
 	Common::Rational targetRate = rate;
 
-	if (rate < 0) {
-		// TODO: Implement support for this
+	// Attempt to set the reverse
+	if (!setReverse(rate < 0)) {
+		assert(rate < 0); // We shouldn't fail for forward.
 		warning("Cannot set custom rate to backwards");
+		setReverse(false);
 		targetRate = 1;
 
 		if (_playbackRate == targetRate)
diff --git a/video/video_decoder.h b/video/video_decoder.h
index 5fec52cf42..d0a6e08005 100644
--- a/video/video_decoder.h
+++ b/video/video_decoder.h
@@ -353,6 +353,17 @@ public:
 	 */
 	void setDefaultHighColorFormat(const Graphics::PixelFormat &format) { _defaultHighColorFormat = format; }
 
+	/**
+	 * Set the video to decode frames in reverse.
+	 *
+	 * By default, VideoDecoder will decode forward.
+	 *
+	 * @note This is used by setRate()
+	 * @note This will not work if an audio track is present
+	 * @param reverse true for reverse, false for forward
+	 * @return true on success, false otherwise
+	 */
+	bool setReverse(bool reverse);
 
 	/////////////////////////////////////////
 	// Audio Control
@@ -551,6 +562,21 @@ protected:
 		 * should only be used by VideoDecoder::seekToFrame().
 		 */
 		virtual Audio::Timestamp getFrameTime(uint frame) const;
+
+		/**
+		 * Set the video track to play in reverse or forward.
+		 *
+		 * By default, a VideoTrack must decode forward.
+		 *
+		 * @param reverse true for reverse, false for forward
+		 * @return true for success, false for failure
+		 */
+		virtual bool setReverse(bool reverse) { return !reverse; }
+
+		/**
+		 * Is the video track set to play in reverse?
+		 */
+		virtual bool isReversed() const { return false; }
 	};
 
 	/**