VIDEO: Add reverse playback support to AviDecoder

video/avi_decoder.cpp

@@ -458,6 +458,8 @@ void AVIDecoder::handleNextPacket(TrackStatus &status) {
 
 	// Seek to where we shall start searching
 	_fileStream->seek(status.chunkSearchOffset);
+	bool isReversed = false;
+	AVIVideoTrack *videoTrack = nullptr;
 
 	for (;;) {
 		// If there's no more to search, bail out
@@ -511,7 +513,8 @@ void AVIDecoder::handleNextPacket(TrackStatus &status) {
 			if (!shouldQueueAudio(status))
 				break;
 		} else {
-			AVIVideoTrack *videoTrack = (AVIVideoTrack *)status.track;
+			videoTrack = (AVIVideoTrack *)status.track;
+			isReversed = videoTrack->isReversed();
 
 			if (getStreamType(nextTag) == kStreamTypePaletteChange) {
 				// Palette Change
@@ -524,8 +527,15 @@ void AVIDecoder::handleNextPacket(TrackStatus &status) {
 		}
 	}
 
+	if (!isReversed) {
 		// Start us off in this position next time
 		status.chunkSearchOffset = _fileStream->pos();
+	} else {
+		// Seek to the prior frame
+		assert(videoTrack);
+		Audio::Timestamp time = videoTrack->getFrameTime(getCurFrame());
+		seekIntern(time);
+	}
 }
 
 bool AVIDecoder::shouldQueueAudio(TrackStatus& status) {
@@ -566,6 +576,8 @@ uint AVIDecoder::getVideoTrackOffset(uint trackIndex, uint frameNumber) {
 }
 
 bool AVIDecoder::seekIntern(const Audio::Timestamp &time) {
+	uint frame;
+
 	// Can't seek beyond the end
 	if (time > getDuration())
 		return false;
@@ -574,10 +586,11 @@ bool AVIDecoder::seekIntern(const Audio::Timestamp &time) {
 	AVIVideoTrack *videoTrack = (AVIVideoTrack *)_videoTracks[0].track;
 	uint32 videoIndex = _videoTracks[0].index;
 
-	// If we seek directly to the end, just mark the tracks as over
 	if (time == getDuration()) {
 		videoTrack->setCurFrame(videoTrack->getFrameCount() - 1);
 
+		if (!videoTrack->isReversed()) {
+			// Since we're at the end, just mark the tracks as over
 			for (TrackListIterator it = getTrackListBegin(); it != getTrackListEnd(); it++)
 				if ((*it)->getTrackType() == Track::kTrackTypeAudio)
 					((AVIAudioTrack *)*it)->resetStream();
@@ -585,8 +598,11 @@ bool AVIDecoder::seekIntern(const Audio::Timestamp &time) {
 			return true;
 		}
 
+		frame = videoTrack->getFrameCount() - 1;
+	} else {
 		// Get the frame we should be on at this time
-	uint frame = videoTrack->getFrameAtTime(time);
+		frame = videoTrack->getFrameAtTime(time);
+	}
 
 	// Reset any palette, if necessary
 	videoTrack->useInitialPalette();
@@ -821,6 +837,7 @@ AVIDecoder::AVIVideoTrack::AVIVideoTrack(int frameCount, const AVIStreamHeader &
 	_videoCodec = createCodec();
 	_lastFrame = 0;
 	_curFrame = -1;
+	_reversed = false;
 
 	useInitialPalette();
 }
@@ -840,7 +857,12 @@ void AVIDecoder::AVIVideoTrack::decodeFrame(Common::SeekableReadStream *stream)
 	}
 
 	delete stream;
+
+	if (!_reversed) {
 		_curFrame++;
+	} else {
+		_curFrame--;
+	}
 }
 
 Graphics::PixelFormat AVIDecoder::AVIVideoTrack::getPixelFormat() const {
@@ -923,6 +945,23 @@ bool AVIDecoder::AVIVideoTrack::hasDirtyPalette() const {
 	return _dirtyPalette;
 }
 
+bool AVIDecoder::AVIVideoTrack::setReverse(bool reverse) {
+	if (isRewindable()) {
+		// Track is rewindable, so reversing is allowed
+		_reversed = reverse;
+		return true;
+	}
+
+	return !reverse;
+}
+
+bool AVIDecoder::AVIVideoTrack::endOfTrack() const {
+	if (_reversed)
+		return _curFrame < 0;
+
+	return _curFrame >= (getFrameCount() - 1);
+}
+
 bool AVIDecoder::AVIVideoTrack::canDither() const {
 	return _videoCodec && _videoCodec->canDither(Image::Codec::kDitherTypeVFW);
 }

video/avi_decoder.h

@@ -210,6 +210,25 @@ protected:
 		bool isRewindable() const { return true; }
 		bool rewind();
 
+		/**
+		 * 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);
+
+		/**
+		 * Is the video track set to play in reverse?
+		 */
+		virtual bool isReversed() const { return _reversed; }
+
+		/**
+		 * Returns true if at the end of the video track
+		 */
+		virtual bool endOfTrack() const;
 	protected:
 		Common::Rational getFrameRate() const { return Common::Rational(_vidsHeader.rate, _vidsHeader.scale); }
 
@@ -220,6 +239,7 @@ protected:
 		byte *_initialPalette;
 		mutable bool _dirtyPalette;
 		int _frameCount, _curFrame;
+		bool _reversed;
 
 		Image::Codec *_videoCodec;
 		const Graphics::Surface *_lastFrame;