ZVISION: LZSSReadStream - Decompress directly to the destination buffer instead of an intermediate buffer

3 files changed, 20 insertions, 61 deletions

diff --git a/engines/zvision/image.cpp b/engines/zvision/image.cpp
index 6e6b802739..cacfec302c 100644
--- a/engines/zvision/image.cpp
+++ b/engines/zvision/image.cpp
@@ -52,9 +52,9 @@ void ZVision::renderImageToScreen(const Common::String &fileName, uint32 x, uint
 		uint32 width = file.readSint32LE();
 		uint32 height = file.readSint32LE();
 
-		LzssReadStream stream(&file, false, decompressedSize);
-		byte *buffer = new byte[stream.currentSize()];
-		stream.read(buffer, stream.currentSize());
+		LzssReadStream stream(&file);
+		byte *buffer = new byte[decompressedSize];
+		stream.read(buffer, decompressedSize);
 
 		_system->copyRectToScreen(buffer, width * 2, x, y, width, height);
 	} else {
diff --git a/engines/zvision/lzss_read_stream.cpp b/engines/zvision/lzss_read_stream.cpp
index 2d7acdb8ce..35c708a6c7 100644
--- a/engines/zvision/lzss_read_stream.cpp
+++ b/engines/zvision/lzss_read_stream.cpp
@@ -26,7 +26,7 @@
 
 namespace ZVision {
 
-LzssReadStream::LzssReadStream(Common::SeekableReadStream *source, bool stream, uint32 decompressedSize)
+LzssReadStream::LzssReadStream(Common::SeekableReadStream *source)
 		: _source(source),
 		  // It's convention to set the starting cursor position to blockSize - 16
 		  _windowCursor(0x0FEE),
@@ -34,24 +34,12 @@ LzssReadStream::LzssReadStream(Common::SeekableReadStream *source, bool stream,
 		  _eosFlag(false) {
 	// Clear the window to null
 	memset(_window, 0, _blockSize);
-
-	// Reserve space in the destination buffer
-	// TODO: Make a better guess
-	if (decompressedSize == _npos) {
-		decompressedSize = source->size();
-	}
-	_destination.reserve(decompressedSize);
-
-	if (stream)
-		decompressBytes(_blockSize);
-	else
-		decompressAll();
 }
 
-void LzssReadStream::decompressBytes(uint32 numberOfBytes) {
-	uint32 bytesRead = 0;
+uint32 LzssReadStream::decompressBytes(byte *destination, uint32 numberOfBytes) {
+	uint32 destinationCursor = 0;
 
-	while (!_source->eos() && bytesRead <= numberOfBytes) {
+	while (destinationCursor < numberOfBytes) {
 		byte flagbyte = _source->readByte();
 		if (_source->eos())
 			break;
@@ -61,12 +49,11 @@ void LzssReadStream::decompressBytes(uint32 numberOfBytes) {
 			if ((flagbyte & mask) == mask)
 			{
 				byte data = _source->readByte();
-				bytesRead++;
 				if (_source->eos())
-					break;
+					return destinationCursor;
 
 				_window[_windowCursor] = data;
-				_destination.push_back(data);
+				destination[destinationCursor++] = data;
 
 				// Increment and wrap the window cursor
 				_windowCursor = (_windowCursor + 1) & 0xFFF;
@@ -74,14 +61,12 @@ void LzssReadStream::decompressBytes(uint32 numberOfBytes) {
 			else
 			{
 				byte low = _source->readByte();
-				bytesRead++;
 				if (_source->eos())
-					break;
+					return destinationCursor;
 
 				byte high = _source->readByte();
-				bytesRead++;
 				if (_source->eos())
-					break;
+					return destinationCursor;
 
 				uint16 length = (high & 0xF) + 2;
 				uint16 offset = low | ((high & 0xF0)<<4);
@@ -90,7 +75,7 @@ void LzssReadStream::decompressBytes(uint32 numberOfBytes) {
 				{
 					byte temp = _window[(offset + j) & 0xFFF];
 					_window[_windowCursor] = temp;
-					_destination.push_back(temp);
+					destination[destinationCursor++] = temp;
 					_windowCursor = (_windowCursor + 1) & 0xFFF;
 				}
 			};
@@ -98,10 +83,8 @@ void LzssReadStream::decompressBytes(uint32 numberOfBytes) {
 			mask = mask << 1;
 		}
 	}
-}
 
-void LzssReadStream::decompressAll() {
-	decompressBytes(_source->size());
+	return destinationCursor;
 }
 
 bool LzssReadStream::eos() const {
@@ -109,30 +92,13 @@ bool LzssReadStream::eos() const {
 }
 
 uint32 LzssReadStream::read(void *dataPtr, uint32 dataSize) {
-	// Check if there are enough bytes available
-	// If not, keep decompressing until we have enough bytes or until we reach EOS
-	while (dataSize > _destination.size() - _readCursor) {
-		// Check if we can read any more data from source
-		if (_source->eos()) {
-			// Shorten the dataSize to what we have left and flag that we're at EOS
-			dataSize = _destination.size() - _readCursor;
-			_eosFlag = true;
-			break;
-		}
-
-		decompressBytes(_blockSize);
-	}
-
-	if (dataSize > 0) {
-		memcpy(dataPtr, _destination.begin() + _readCursor, dataSize);
-		_readCursor += dataSize;
+	uint32 bytesRead = decompressBytes(static_cast<byte *>(dataPtr), dataSize);
+	if (bytesRead < dataSize) {
+		// Flag that we're at EOS
+		_eosFlag = true;
 	}
 
 	return dataSize;
 }
 
-uint32 LzssReadStream::currentSize() const {
-	return _destination.size();
-}
-
 } // End of namespace ZVision
diff --git a/engines/zvision/lzss_read_stream.h b/engines/zvision/lzss_read_stream.h
index 142bf9e1a2..0dea25b325 100644
--- a/engines/zvision/lzss_read_stream.h
+++ b/engines/zvision/lzss_read_stream.h
@@ -34,14 +34,11 @@ class LzssReadStream : public Common::ReadStream {
 public:
 	/**
 	 * A class that decompresses LZSS data and implements ReadStream for easy access 
-	 * to the decompiled data. It can either decompress all the data in the beginning 
-	 * or decompress as needed by read().
+	 * to the decompiled data.
 	 *
 	 * @param source              The source data
-	 * @param stream			  Decompress the data as needed (true) or all at once (false)
-	 * @param decompressedSize    The size of the decompressed data. If npos, the class will choose a size and grow as needed
 	 */
-	LzssReadStream(Common::SeekableReadStream *source, bool stream = true, uint32 decompressedSize = _npos);
+	LzssReadStream(Common::SeekableReadStream *source);
 
 public:
 	static const uint32 _npos = 0xFFFFFFFFu;
@@ -49,7 +46,6 @@ public:
 
 private:
 	Common::SeekableReadStream *_source;
-	Common::Array<char> _destination;
 	char _window[_blockSize];
 	uint16 _windowCursor;
 	uint32 _readCursor;
@@ -58,7 +54,6 @@ private:
 public:
 	bool eos() const;
 	uint32 read(void *dataPtr, uint32 dataSize);
-	uint32 currentSize() const;
 
 private:
 	/**
@@ -66,9 +61,7 @@ private:
 	 *
 	 * @param numberOfBytes    How many bytes to decompress. This is a count of source bytes, not destination bytes
 	 */
-	void decompressBytes(uint32 numberOfBytes);
-	/** Decompress all of the source stream. */
-	void decompressAll();
+	uint32 decompressBytes(byte* destination, uint32 numberOfBytes);
 };
 
 }