bfg.h

/*

BFG - Block-Based Fast Graphics format for lossless image compression.

Seb Seager


## License

Copyright (c) 2022, Seb Seager.

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## Motivation

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## Format

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REMEMBER: block length is one more than the int recorded (so 0 = len 1)

TODO
- clear out unnecessary asserts after testing

ASSUMPTIONS
- lookback before beginning of the file all bytes are zeros

##

*/

#include <stdint.h>

#define BFG_MAGIC_TAG (0xBFBFBFBF)
#define BFG_VERSION (1)
#define BFG_MAX_BYTES (UINT32_MAX)
#define BFG_BIT_DEPTH (8)
#define BFG_TAG_BITS (3)
#define BFG_DIFF_BITS (4) /* must divide BFG_BIT_DEPTH */

/* Optionally provide custom malloc and free implementations. */
#ifndef BFG_MALLOC
#define BFG_MALLOC(sz) malloc(sz)
#define BFG_REALLOC(ptr, sz) realloc(ptr, sz)
#define BFG_FREE(ptr) free(ptr)
#endif

/* Tags appearing in the first BFG_TAG_BITS of each block header. No tag
 * with a value < 0 should ever appear in a valid BFG file. These are provided
 * for ease of implementation only. */
typedef enum {
  BFG_BLOCK_FULL = 0,
  BFG_BLOCK_RUN = 1,
  BFG_BLOCK_DIFF = 2,
} bfg_block_type_t;

/* Internal image representation generated by any *_decode function. */
typedef struct bfg_raw {
  uint32_t width;
  uint32_t height;
  uint8_t n_channels;
  uint8_t *pixels;
} * bfg_raw_t;

/* Info struct for a BFG encoding. Filled out by bfg_encode and written to the
 * beginning of a BFG file by bfg_write as the header block. */
typedef struct bfg_info {
  uint32_t magic_tag;
  uint32_t version;
  uint32_t width;
  uint32_t height;
  uint32_t n_bytes;
  uint8_t n_channels;
  uint8_t color_mode;
  uint8_t bit_depth;
} * bfg_info_t;
// TODO: MAKE THIS DIVISIBLE BY 32 BITS (add another 8 bits)
// TODO: fill out bit_depth

/* Encoded BFG image representation, always of length bfg_info->n_bytes.
 * Generated by bfg_encode and written to a BFG file after the header block. */
typedef uint8_t *bfg_img_t;

void bfg_free(bfg_raw_t raw, bfg_img_t img);

/* Caller must free. */
bfg_img_t bfg_encode(bfg_raw_t raw, bfg_info_t info);

int bfg_decode(bfg_info_t info, bfg_img_t img, bfg_raw_t raw);

int bfg_write(char *fpath, bfg_info_t info, bfg_img_t img);

bfg_img_t bfg_read(char *fpath, bfg_info_t info);