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Modify GifEncode.c and Gif.h to use LZW encoding

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This commit is contained in:
Ray Gardner 2021-02-22 16:25:00 -07:00
parent d40211254c
commit 0acf3514a1
2 changed files with 308 additions and 285 deletions
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37
src/libImaging/Gif.h
View File

@ -11,8 +11,8 @@
#define GIFBITS 12 #define GIFBITS 12
#define GIFTABLE (1 << GIFBITS) #define GIFTABLE (1<<GIFBITS)
#define GIFBUFFER (1 << GIFBITS) #define GIFBUFFER (1<<GIFBITS)
typedef struct { typedef struct {
/* CONFIGURATION */ /* CONFIGURATION */
@ -62,11 +62,8 @@ typedef struct {
} GIFDECODERSTATE; } GIFDECODERSTATE;
typedef struct GIFENCODERBLOCK_T { /* For GIF LZW encoder. */
struct GIFENCODERBLOCK_T *next; #define TABLE_SIZE 8192
int size;
UINT8 data[255];
} GIFENCODERBLOCK;
typedef struct { typedef struct {
/* CONFIGURATION */ /* CONFIGURATION */
@ -84,21 +81,17 @@ typedef struct {
/* PRIVATE CONTEXT (set by encoder) */ /* PRIVATE CONTEXT (set by encoder) */
/* Interlace parameters */ /* Interlace parameters */
int step, repeat; int step;
/* Output bit buffer */ /* For GIF LZW encoder. */
INT32 bitbuffer; UINT32 put_state;
int bitcount; UINT32 entry_state;
UINT32 clear_code, end_code, next_code, max_code;
/* Output buffer list (linked list) */ UINT32 code_width, code_bits_left, buf_bits_left;
GIFENCODERBLOCK *block; /* current block */ UINT32 code_buffer;
GIFENCODERBLOCK *flush; /* output queue */ UINT32 head, tail;
GIFENCODERBLOCK *free; /* if not null, use this */ int probe;
UINT32 code;
/* Fields used for run-length encoding */ UINT32 codes[TABLE_SIZE];
int first; /* true if we haven't read the first pixel */
int last; /* last byte value seen */
int count; /* how many bytes with that value we've seen */
int lastcode;
} GIFENCODERSTATE; } GIFENCODERSTATE;

490
src/libImaging/GifEncode.c
View File

@ -10,6 +10,7 @@
* 98-07-09 fl added interlace write support * 98-07-09 fl added interlace write support
* 99-02-07 fl rewritten, now uses a run-length encoding strategy * 99-02-07 fl rewritten, now uses a run-length encoding strategy
* 99-02-08 fl improved run-length encoding for long runs * 99-02-08 fl improved run-length encoding for long runs
* 2020-12-12 rdg Reworked for LZW compression.
* *
* Copyright (c) Secret Labs AB 1997-99. * Copyright (c) Secret Labs AB 1997-99.
* Copyright (c) Fredrik Lundh 1997. * Copyright (c) Fredrik Lundh 1997.
@ -21,136 +22,199 @@
#include "Gif.h" #include "Gif.h"
/* codes from 0 to 255 are literals */ enum { INIT, ENCODE, FINISH };
#define CLEAR_CODE 256
#define EOF_CODE 257
#define FIRST_CODE 258
#define LAST_CODE 511
enum { INIT, ENCODE, ENCODE_EOF, FLUSH, EXIT }; /* GIF LZW encoder by Raymond Gardner. */
/* Released here under PIL license. */
/* to make things a little less complicated, we use a simple output /* Return values */
queue to hold completed blocks. the following inlined function #define GLZW_OK 0
adds a byte to the current block. it allocates a new block if #define GLZW_NO_INPUT_AVAIL 1
necessary. */ #define GLZW_NO_OUTPUT_AVAIL 2
#define GLZW_INTERNAL_ERROR 3
static inline int #define CODE_LIMIT 4096
emit(GIFENCODERSTATE *context, int byte) {
/* write a byte to the output buffer */
if (!context->block || context->block->size == 255) { /* Values of entry_state */
GIFENCODERBLOCK *block; enum { LZW_INITIAL, LZW_TRY_IN1, LZW_TRY_IN2, LZW_TRY_OUT1, LZW_TRY_OUT2,
LZW_FINISHED };
/* no room in the current block (or no current block); /* Values of control_state */
allocate a new one */ enum { PUT_HEAD, PUT_INIT_CLEAR, PUT_CLEAR, PUT_LAST_HEAD, PUT_END };
/* add current block to end of flush queue */ static void glzwe_reset(GIFENCODERSTATE *st) {
if (context->block) { st->next_code = st->end_code + 1;
block = context->flush; st->max_code = 2 * st->clear_code - 1;
while (block && block->next) { st->code_width = st->bits + 1;
block = block->next; memset(st->codes, 0, sizeof(st->codes));
}
if (block) {
block->next = context->block;
} else {
context->flush = context->block;
}
}
/* get a new block */
if (context->free) {
block = context->free;
context->free = NULL;
} else {
/* malloc check ok, small constant allocation */
block = malloc(sizeof(GIFENCODERBLOCK));
if (!block) {
return 0;
}
}
block->size = 0;
block->next = NULL;
context->block = block;
}
/* write new byte to block */
context->block->data[context->block->size++] = byte;
return 1;
} }
/* write a code word to the current block. this is a macro to make static void glzwe_init(GIFENCODERSTATE *st) {
sure it's inlined on all platforms */ st->clear_code = 1 << st->bits;
st->end_code = st->clear_code + 1;
glzwe_reset(st);
st->entry_state = LZW_INITIAL;
st->buf_bits_left = 8;
st->code_buffer = 0;
}
#define EMIT(code) \ static int glzwe(GIFENCODERSTATE *st, const UINT8 *in_ptr, UINT8 *out_ptr,
{ \ UINT32 *in_avail, UINT32 *out_avail,
context->bitbuffer |= ((INT32)(code)) << context->bitcount; \ UINT32 end_of_data) {
context->bitcount += 9; \ switch (st->entry_state) {
while (context->bitcount >= 8) { \
if (!emit(context, (UINT8)context->bitbuffer)) { \ case LZW_TRY_IN1:
state->errcode = IMAGING_CODEC_MEMORY; \ get_first_byte:
return 0; \ if (!*in_avail) {
} \ if (end_of_data) {
context->bitbuffer >>= 8; \ goto end_of_data;
context->bitcount -= 8; \ }
} \ st->entry_state = LZW_TRY_IN1;
return GLZW_NO_INPUT_AVAIL;
}
st->head = *in_ptr++;
(*in_avail)--;
case LZW_TRY_IN2:
encode_loop:
if (!*in_avail) {
if (end_of_data) {
st->code = st->head;
st->put_state = PUT_LAST_HEAD;
goto put_code;
}
st->entry_state = LZW_TRY_IN2;
return GLZW_NO_INPUT_AVAIL;
}
st->tail = *in_ptr++;
(*in_avail)--;
/* Knuth TAOCP vol 3 sec. 6.4 algorithm D. */
/* Hash found experimentally to be pretty good. */
/* This works ONLY with TABLE_SIZE a power of 2. */
st->probe = ((st->head ^ (st->tail << 6)) * 31) & (TABLE_SIZE - 1);
while (st->codes[st->probe]) {
if ((st->codes[st->probe] & 0xFFFFF) ==
((st->head << 8) | st->tail)) {
st->head = st->codes[st->probe] >> 20;
goto encode_loop;
} else {
/* Reprobe decrement must be nonzero and relatively prime to table
* size. So, any odd positive number for power-of-2 size. */
if ((st->probe -= ((st->tail << 2) | 1)) < 0) {
st->probe += TABLE_SIZE;
}
}
}
/* Key not found, probe is at empty slot. */
st->code = st->head;
st->put_state = PUT_HEAD;
goto put_code;
insert_code_or_clear: /* jump here after put_code */
if (st->next_code < CODE_LIMIT) {
st->codes[st->probe] = (st->next_code << 20) |
(st->head << 8) | st->tail;
if (st->next_code > st->max_code) {
st->max_code = st->max_code * 2 + 1;
st->code_width++;
}
st->next_code++;
} else {
st->code = st->clear_code;
st->put_state = PUT_CLEAR;
goto put_code;
reset_after_clear: /* jump here after put_code */
glzwe_reset(st);
}
st->head = st->tail;
goto encode_loop;
case LZW_INITIAL:
glzwe_reset(st);
st->code = st->clear_code;
st->put_state = PUT_INIT_CLEAR;
put_code:
st->code_bits_left = st->code_width;
check_buf_bits:
if (!st->buf_bits_left) { /* out buffer full */
case LZW_TRY_OUT1:
if (!*out_avail) {
st->entry_state = LZW_TRY_OUT1;
return GLZW_NO_OUTPUT_AVAIL;
}
*out_ptr++ = st->code_buffer;
(*out_avail)--;
st->code_buffer = 0;
st->buf_bits_left = 8;
}
/* code bits to pack */
UINT32 n = st->buf_bits_left < st->code_bits_left
? st->buf_bits_left : st->code_bits_left;
st->code_buffer |=
(st->code & ((1 << n) - 1)) << (8 - st->buf_bits_left);
st->code >>= n;
st->buf_bits_left -= n;
st->code_bits_left -= n;
if (st->code_bits_left)
goto check_buf_bits;
switch (st->put_state) {
case PUT_INIT_CLEAR:
goto get_first_byte;
case PUT_HEAD:
goto insert_code_or_clear;
case PUT_CLEAR:
goto reset_after_clear;
case PUT_LAST_HEAD:
goto end_of_data;
case PUT_END:
goto flush_code_buffer;
default:
return GLZW_INTERNAL_ERROR;
} }
/* write a run. we use a combination of literals and combinations of end_of_data:
literals. this can give quite decent compression for images with st->code = st->end_code;
long stretches of identical pixels. but remember: if you want st->put_state = PUT_END;
really good compression, use another file format. */ goto put_code;
flush_code_buffer: /* jump here after put_code */
if (st->buf_bits_left < 8) {
#define EMIT_RUN(label) \ case LZW_TRY_OUT2:
{ \ if (!*out_avail) {
label: \ st->entry_state = LZW_TRY_OUT2;
while (context->count > 0) { \ return GLZW_NO_OUTPUT_AVAIL;
int run = 2; \
EMIT(context->last); \
context->count--; \
if (state->count++ == LAST_CODE) { \
EMIT(CLEAR_CODE); \
state->count = FIRST_CODE; \
goto label; \
} \
while (context->count >= run) { \
EMIT(state->count - 1); \
context->count -= run; \
run++; \
if (state->count++ == LAST_CODE) { \
EMIT(CLEAR_CODE); \
state->count = FIRST_CODE; \
goto label; \
} \
} \
if (context->count > 1) { \
EMIT(state->count - 1 - (run - context->count)); \
context->count = 0; \
if (state->count++ == LAST_CODE) { \
EMIT(CLEAR_CODE); \
state->count = FIRST_CODE; \
} \
break; \
} \
} \
} }
*out_ptr++ = st->code_buffer;
(*out_avail)--;
}
st->entry_state = LZW_FINISHED;
return GLZW_OK;
case LZW_FINISHED:
return GLZW_OK;
default:
return GLZW_INTERNAL_ERROR;
}
}
/* -END- GIF LZW encoder. */
int int
ImagingGifEncode(Imaging im, ImagingCodecState state, UINT8 *buf, int bytes) { ImagingGifEncode(Imaging im, ImagingCodecState state, UINT8* buf, int bytes) {
UINT8 *ptr; UINT8* ptr;
int this; UINT8* sub_block_ptr;
UINT8* sub_block_limit;
UINT8* buf_limit;
GIFENCODERSTATE *context = (GIFENCODERSTATE*) state->context;
int r;
GIFENCODERBLOCK *block; UINT32 in_avail, in_used;
GIFENCODERSTATE *context = (GIFENCODERSTATE *)state->context; UINT32 out_avail, out_used;
if (!state->state) { if (state->state == INIT) {
/* place a clear code in the output buffer */ state->state = ENCODE;
context->bitbuffer = CLEAR_CODE; glzwe_init(context);
context->bitcount = 9;
state->count = FIRST_CODE;
if (context->interlace) { if (context->interlace) {
context->interlace = 1; context->interlace = 1;
@ -159,53 +223,85 @@ ImagingGifEncode(Imaging im, ImagingCodecState state, UINT8 *buf, int bytes) {
context->step = 1; context->step = 1;
} }
context->last = -1; /* Need at least 2 bytes for data sub-block; 5 for empty image */
if (bytes < 5) {
state->errcode = IMAGING_CODEC_CONFIG;
return 0;
}
/* sanity check */ /* sanity check */
if (state->xsize <= 0 || state->ysize <= 0) { if (state->xsize <= 0 || state->ysize <= 0) {
state->state = ENCODE_EOF; /* Is this better than an error return? */
/* This will handle any legal "LZW Minimum Code Size" */
memset(buf, 0, 5);
in_avail = 0;
out_avail = 5;
r = glzwe(context, (const UINT8 *)"", buf + 1, &in_avail, &out_avail, 1);
if (r == GLZW_OK) {
r = 5 - out_avail;
if (r < 1 || r > 3) {
state->errcode = IMAGING_CODEC_BROKEN;
return 0;
}
buf[0] = r;
state->errcode = IMAGING_CODEC_END;
return r + 2;
} else {
/* Should not be possible unless something external to this
* routine messes with our state data */
state->errcode = IMAGING_CODEC_BROKEN;
return 0;
} }
} }
/* Init state->x to make if() below true the first time through. */
state->x = state->xsize;
}
ptr = buf; buf_limit = buf + bytes;
sub_block_limit = sub_block_ptr = ptr = buf;
/* On entry, buf is output buffer, bytes is space available in buf.
* Loop here getting input until buf is full or image is all encoded. */
for (;;) { for (;;) {
switch (state->state) { /* Set up sub-block ptr and limit. sub_block_ptr stays at beginning
case INIT: * of sub-block until it is full. ptr will advance when any data is
case ENCODE: * placed in buf.
*/
/* identify and store a run of pixels */ if (ptr >= sub_block_limit) {
if (buf_limit - ptr < 2) { /* Need at least 2 for data sub-block */
if (state->x == 0 || state->x >= state->xsize) { return ptr - buf;
if (!context->interlace && state->y >= state->ysize) { }
state->state = ENCODE_EOF; sub_block_ptr = ptr;
break; sub_block_limit = sub_block_ptr +
(256 < buf_limit - sub_block_ptr ?
256 : buf_limit - sub_block_ptr);
*ptr++ = 0;
} }
if (context->flush) { /* Get next row of pixels. */
state->state = FLUSH; /* This if() originally tested state->x==0 for the first time through.
break; * This no longer works, as the loop will not advance state->x if
* glzwe() does not consume any input; this would advance the row
* spuriously. Now pre-init state->x above for first time, and avoid
* entering if() when state->state is FINISH, or it will loop
* infinitely.
*/
if (state->x >= state->xsize && state->state == ENCODE) {
if (!context->interlace && state->y >= state->ysize) {
state->state = FINISH;
continue;
} }
/* get another line of data */ /* get another line of data */
state->shuffle( state->shuffle(
state->buffer, state->buffer,
(UINT8 *)im->image[state->y + state->yoff] + (UINT8*) im->image[state->y + state->yoff] +
state->xoff * im->pixelsize, state->xoff * im->pixelsize, state->xsize
state->xsize); );
state->x = 0; state->x = 0;
if (state->state == INIT) {
/* preload the run-length buffer and get going */
context->last = state->buffer[0];
context->count = state->x = 1;
state->state = ENCODE;
}
/* step forward, according to the interlace settings */ /* step forward, according to the interlace settings */
state->y += context->step; state->y += context->step;
while (context->interlace && state->y >= state->ysize) while (context->interlace && state->y >= state->ysize) {
switch (context->interlace) { switch (context->interlace) {
case 1: case 1:
state->y = 4; state->y = 4;
@ -226,99 +322,33 @@ ImagingGifEncode(Imaging im, ImagingCodecState state, UINT8 *buf, int bytes) {
context->interlace = 0; context->interlace = 0;
} }
} }
/* Potential special case for xsize==1 */
if (state->x < state->xsize) {
this = state->buffer[state->x++];
} else {
EMIT_RUN(label0);
break;
} }
if (this == context->last) { in_avail = state->xsize - state->x; /* bytes left in line */
context->count++; out_avail = sub_block_limit - ptr; /* bytes left in sub-block */
} else { r = glzwe(context, &state->buffer[state->x], ptr, &in_avail,
EMIT_RUN(label1); &out_avail, state->state == FINISH);
context->last = this; out_used = sub_block_limit - ptr - out_avail;
context->count = 1; *sub_block_ptr += out_used;
} ptr += out_used;
break; in_used = state->xsize - state->x - in_avail;
state->x += in_used;
case ENCODE_EOF: if (r == GLZW_OK) {
/* Should not be possible when end-of-data flag is false. */
/* write the final run */
EMIT_RUN(label2);
/* write an end of image marker */
EMIT(EOF_CODE);
/* empty the bit buffer */
while (context->bitcount > 0) {
if (!emit(context, (UINT8)context->bitbuffer)) {
state->errcode = IMAGING_CODEC_MEMORY;
return 0;
}
context->bitbuffer >>= 8;
context->bitcount -= 8;
}
/* flush the last block, and exit */
if (context->block) {
GIFENCODERBLOCK *block;
block = context->flush;
while (block && block->next) {
block = block->next;
}
if (block) {
block->next = context->block;
} else {
context->flush = context->block;
}
context->block = NULL;
}
state->state = EXIT;
/* fall through... */
case EXIT:
case FLUSH:
while (context->flush) {
/* get a block from the flush queue */
block = context->flush;
if (block->size > 0) {
/* make sure it fits into the output buffer */
if (bytes < block->size + 1) {
return ptr - buf;
}
ptr[0] = block->size;
memcpy(ptr + 1, block->data, block->size);
ptr += block->size + 1;
bytes -= block->size + 1;
}
context->flush = block->next;
if (context->free) {
free(context->free);
}
context->free = block;
}
if (state->state == EXIT) {
/* this was the last block! */
if (context->free) {
free(context->free);
}
state->errcode = IMAGING_CODEC_END; state->errcode = IMAGING_CODEC_END;
return ptr - buf; return ptr - buf;
} } else if (r == GLZW_NO_INPUT_AVAIL) {
/* Used all the input line; get another line */
state->state = ENCODE; continue;
break; } else if (r == GLZW_NO_OUTPUT_AVAIL) {
/* subblock is full */
continue;
} else {
/* Should not be possible unless something external to this
* routine messes with our state data */
state->errcode = IMAGING_CODEC_BROKEN;
return 0;
} }
} }
} }