//基于DCT的靜態圖像壓縮編碼類

//Huffman碼表
typedef struct tag_HUFFMAN_TABLE {
		unsigned int	code[256];	// code for each symbol 
		char			size[256];	// length of code for each symbol 
		//If no code has been allocated for a symbol S, size[S] is 0 

		/* These two fields directly represent the contents of a JPEG DHT marker */
		unsigned char bits[17];		/* bits[k] = # of symbols with codes of */
		/* length k bits; bits[0] is unused */
		unsigned char huffval[256];		/* The symbols, in order of incr code length */
								/* This field is used only during compression.  It's initialized FALSE when
								* the table is created, and set TRUE when it's been output to the file.
								* You could suppress output of a table by setting this to TRUE.
								* (See jpeg_suppress_tables for an example.)*/
}HUFFMAN_TABLE;


class CompressEncode
{

private:
	
	////////////////////////////////////////////////////////////////////////////
	//	Following data members should be computed in initialization

	unsigned short m_nQuality, m_nScale;

	//RGB轉化YCbCr顏色對應表
	int m_RToY[256],	m_GToY[256],	m_BToY[256];
	int m_RToCb[256],	m_GToCb[256],	m_BToCb[256];
	int m_RToCr[256],	m_GToCr[256],	m_BToCr[256];

	//	To speed up, we precompute two DCT quant tables
	unsigned short m_qtblY[64], m_qtblCbCr[64];

	//用來寫入JPG文件頭
	unsigned char m_dqtY[64], m_dqtCbCr[64];

	HUFFMAN_TABLE m_htblYDC, m_htblYAC, m_htblCbCrDC, m_htblCbCrAC;

	////////////////////////////////////////////////////////////////////////////
	
	////////////////////////////////////////////////////////////////////////////
	//	Following are should be initialized for compressing every image

	unsigned short m_nWidth, m_nHeight;

	//	Three dc records, used for dc differentize for Y/Cb/Cr
	int m_dcY, m_dcCb, m_dcCr;

	//	The size (in bits) and value (in 4 byte buffer) to be written out
	int m_nPutBits, m_nPutVal;

	unsigned char *m_pOutBuf;

	////////////////////////////////////////////////////////////////////////////

private:

	void InitEncoder( void );
	
	void InitColorTable( void );

	void InitQuantTable( void );

	void ScaleQuantTable(
		unsigned short* tblRst,	
		unsigned char* tblStd,		
		unsigned short* tblAan	
		);

	void ScaleTable(unsigned char* tbl, int scale, int max);


	void InitHuffmanTable( void );

	void ComputeHuffmanTable(
		unsigned char *	pBits, 
		unsigned char * pVal,
		HUFFMAN_TABLE * pTbl	
		);

	bool CompressOneTile(
		unsigned char * pBgr	//source data, in BGR format	
	);

	void BGRToYCbCr(	
		unsigned char * pBgr,	//tile source data, in BGR format, 768 bytes
		unsigned char * pY,		//out, Illuminance, 256 bytes
		unsigned char * pCb,	//out, Cb, 256 bytes
		unsigned char * pCr		//out, Cr, 256 bytes
		);
	
	void BGRToYCbCrEx(	
		unsigned char * pBgr,	//in, tile data, in BGR format, 768 bytes
		int * pBlock			//out, Y: 256; Cb: 64; Cr: 64 
		);
	
	void ForwardDct( 
		int* data,	//source data, length is 64 
		int* coef	//output dct coefficients
		);
	
	void Quantize( 
		int* coef,	//coef is both in and out
		int iBlock	//block id; Y: 0,1,2,3; Cb: 4; Cr: 5
		);

	bool HuffmanEncode( 
		int* pCoef,				//	DCT coefficients
		int iBlock				//	0,1,2,3:Y; 4:Cb; 5:Cr;
		);

	bool EmitBits(
		unsigned int code,		//Huffman code
		int size				//Size in bits of the Huffman code
		);

	void EmitLeftBits(void);

	void WriteJpegHeader(void);	
	void write_sos(void);
	void write_sof(int code);
	void write_app0(void);
	void write_soi(void);
	void write_dht(int IsCbCr, int IsAc);
	void write_dqt(int index);
		
public:
	
	CompressEncode();			//default quality is 50

	CompressEncode( int nQuality );

	~CompressEncode();

	bool CompressImage(	
		unsigned char *pInBuf,	//source data, bgr format, 3 bytes per pixel
		unsigned char *pOutBuf,	//destination buffer, in jpg format
		int nWidthPix,			//image width in pixels
		int nHeight,			//height
		int& nOutputBytes		//return number of bytes being written
		);
};