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批量生成函数注释
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// jpge.h - C++ class for JPEG compression.
// Public domain, Rich Geldreich <richgel99@gmail.com>
// Alex Evans: Added RGBA support, linear memory allocator.
#ifndef JPEG_ENCODER_H
#define JPEG_ENCODER_H
#include <stdint.h>
namespace jpge
{
typedef unsigned char uint8;
typedef signed short int16;
typedef signed int int32;
typedef unsigned short uint16;
typedef unsigned int uint32;
typedef unsigned int uint;
// JPEG chroma subsampling factors. Y_ONLY (grayscale images) and H2V2 (color images) are the most common.
enum subsampling_t { Y_ONLY = 0, H1V1 = 1, H2V1 = 2, H2V2 = 3 };
// JPEG compression parameters structure.
struct params
{
inline params() : m_quality(85), m_subsampling(H2V2), m_no_chroma_discrim_flag(false), m_two_pass_flag(false) { }
inline bool check_valid() const
{
if ((m_quality < 1) || (m_quality > 100)) return false;
if ((uint)m_subsampling > (uint)H2V2) return false;
return true;
}
// Quality: 1-100, higher is better. Typical values are around 50-95.
int m_quality;
// m_subsampling:
// 0 = Y (grayscale) only
// 1 = YCbCr, no subsampling (H1V1, YCbCr 1x1x1, 3 blocks per MCU)
// 2 = YCbCr, H2V1 subsampling (YCbCr 2x1x1, 4 blocks per MCU)
// 3 = YCbCr, H2V2 subsampling (YCbCr 4x1x1, 6 blocks per MCU-- very common)
subsampling_t m_subsampling;
// Disables CbCr discrimination - only intended for testing.
// If true, the Y quantization table is also used for the CbCr channels.
bool m_no_chroma_discrim_flag;
bool m_two_pass_flag;
};
// Writes JPEG image to a file.
// num_channels must be 1 (Y) or 3 (RGB), image pitch must be width*num_channels.
bool compress_image_to_jpeg_file(const char *pFilename, int64_t width, int64_t height, int64_t num_channels, const uint8 *pImage_data, const params &comp_params = params());
// Writes JPEG image to memory buffer.
// On entry, buf_size is the size of the output buffer pointed at by pBuf, which should be at least ~1024 bytes.
// If return value is true, buf_size will be set to the size of the compressed data.
bool compress_image_to_jpeg_file_in_memory(void *pBuf, int64_t &buf_size, int64_t width, int64_t height, int64_t num_channels, const uint8 *pImage_data, const params &comp_params = params());
// Output stream abstract class - used by the jpeg_encoder class to write to the output stream.
// put_buf() is generally called with len==JPGE_OUT_BUF_SIZE bytes, but for headers it'll be called with smaller amounts.
class output_stream
{
public:
virtual ~output_stream() { };
virtual bool put_buf(const void* Pbuf, int64_t len) = 0;
template<class T> inline bool put_obj(const T& obj) { return put_buf(&obj, sizeof(T)); }
};
// Lower level jpeg_encoder class - useful if more control is needed than the above helper functions.
class jpeg_encoder
{
public:
jpeg_encoder();
~jpeg_encoder();
// Initializes the compressor.
// pStream: The stream object to use for writing compressed data.
// params - Compression parameters structure, defined above.
// width, height - Image dimensions.
// channels - May be 1, or 3. 1 indicates grayscale, 3 indicates RGB source data.
// Returns false on out of memory or if a stream write fails.
bool init(output_stream *pStream, int64_t width, int64_t height, int64_t src_channels, const params &comp_params = params());
const params &get_params() const { return m_params; }
// Deinitializes the compressor, freeing any allocated memory. May be called at any time.
void deinit();
uint get_total_passes() const { return m_params.m_two_pass_flag ? 2 : 1; }
inline uint get_cur_pass() { return m_pass_num; }
// Call this method with each source scanline.
// width * src_channels bytes per scanline is expected (RGB or Y format).
// You must call with NULL after all scanlines are processed to finish compression.
// Returns false on out of memory or if a stream write fails.
bool process_scanline(const void* pScanline);
private:
jpeg_encoder(const jpeg_encoder &);
jpeg_encoder &operator =(const jpeg_encoder &);
typedef int32 sample_array_t;
output_stream *m_pStream;
params m_params;
uint8 m_num_components;
uint8 m_comp_h_samp[3], m_comp_v_samp[3];
int m_image_x, m_image_y, m_image_bpp, m_image_bpl;
int m_image_x_mcu, m_image_y_mcu;
int m_image_bpl_xlt, m_image_bpl_mcu;
int m_mcus_per_row;
int m_mcu_x, m_mcu_y;
uint8 *m_mcu_lines[16];
uint8 m_mcu_y_ofs;
sample_array_t m_sample_array[64];
int16 m_coefficient_array[64];
int32 m_quantization_tables[2][64];
uint m_huff_codes[4][256];
uint8 m_huff_code_sizes[4][256];
uint8 m_huff_bits[4][17];
uint8 m_huff_val[4][256];
uint32 m_huff_count[4][256];
int m_last_dc_val[3];
enum { JPGE_OUT_BUF_SIZE = 2048 };
uint8 m_out_buf[JPGE_OUT_BUF_SIZE];
uint8 *m_pOut_buf;
uint m_out_buf_left;
uint32 m_bit_buffer;
uint m_bits_in;
uint8 m_pass_num;
bool m_all_stream_writes_succeeded;
void optimize_huffman_table(int table_num, int table_len);
void emit_byte(uint8 i);
void emit_word(uint i);
void emit_marker(int marker);
void emit_jfif_app0();
void emit_dqt();
void emit_sof();
void emit_dht(uint8 *bits, uint8 *val, int index, bool ac_flag);
void emit_dhts();
void emit_sos();
void emit_markers();
void compute_huffman_table(uint *codes, uint8 *code_sizes, uint8 *bits, uint8 *val);
void compute_quant_table(int32 *dst, int16 *src);
void adjust_quant_table(int32 *dst, int32 *src);
void first_pass_init();
bool second_pass_init();
bool jpg_open(int p_x_res, int p_y_res, int src_channels);
void load_block_8_8_grey(int x);
void load_block_8_8(int x, int y, int c);
void load_block_16_8(int x, int c);
void load_block_16_8_8(int x, int c);
void load_quantized_coefficients(int component_num);
void flush_output_buffer();
void put_bits(uint bits, uint len);
void code_coefficients_pass_one(int component_num);
void code_coefficients_pass_two(int component_num);
void code_block(int component_num);
void process_mcu_row();
bool terminate_pass_one();
bool terminate_pass_two();
bool process_end_of_image();
void load_mcu(const void* src);
void clear();
void init();
};
} // namespace jpge
#endif // JPEG_ENCODER