workbench/libs/jpeg/wrgif.c

   1 /*
   2  * wrgif.c
   3  *
   4  * Copyright (C) 1991-1997, Thomas G. Lane.
   5  * Modified 2015 by Guido Vollbeding.
   6  * This file is part of the Independent JPEG Group's software.
   7  * For conditions of distribution and use, see the accompanying README file.
   8  *
   9  * This file contains routines to write output images in GIF format.
  10  *
  11  **************************************************************************
  12  * NOTE: to avoid entanglements with Unisys' patent on LZW compression,   *
  13  * this code has been modified to output "uncompressed GIF" files.        *
  14  * There is no trace of the LZW algorithm in this file.                   *
  15  **************************************************************************
  16  *
  17  * These routines may need modification for non-Unix environments or
  18  * specialized applications.  As they stand, they assume output to
  19  * an ordinary stdio stream.
  20  */
  21
  22 /*
  23  * This code is loosely based on ppmtogif from the PBMPLUS distribution
  24  * of Feb. 1991.  That file contains the following copyright notice:
  25  *    Based on GIFENCODE by David Rowley <mgardi@watdscu.waterloo.edu>.
  26  *    Lempel-Ziv compression based on "compress" by Spencer W. Thomas et al.
  27  *    Copyright (C) 1989 by Jef Poskanzer.
  28  *    Permission to use, copy, modify, and distribute this software and its
  29  *    documentation for any purpose and without fee is hereby granted, provided
  30  *    that the above copyright notice appear in all copies and that both that
  31  *    copyright notice and this permission notice appear in supporting
  32  *    documentation.  This software is provided "as is" without express or
  33  *    implied warranty.
  34  *
  35  * We are also required to state that
  36  *    "The Graphics Interchange Format(c) is the Copyright property of
  37  *    CompuServe Incorporated. GIF(sm) is a Service Mark property of
  38  *    CompuServe Incorporated."
  39  */
  40
  41 #include "cdjpeg.h"             /* Common decls for cjpeg/djpeg applications */
  42
  43 #ifdef GIF_SUPPORTED
  44
  45
  46 /* Private version of data destination object */
  47
  48 typedef struct {
  49   struct djpeg_dest_struct pub; /* public fields */
  50
  51   j_decompress_ptr cinfo;       /* back link saves passing separate parm */
  52
  53   /* State for packing variable-width codes into a bitstream */
  54   int n_bits;                   /* current number of bits/code */
  55   int maxcode;                  /* maximum code, given n_bits */
  56   INT32 cur_accum;              /* holds bits not yet output */
  57   int cur_bits;                 /* # of bits in cur_accum */
  58
  59   /* State for GIF code assignment */
  60   int ClearCode;                /* clear code (doesn't change) */
  61   int EOFCode;                  /* EOF code (ditto) */
  62   int code_counter;             /* counts output symbols */
  63
  64   /* GIF data packet construction buffer */
  65   int bytesinpkt;               /* # of bytes in current packet */
  66   char packetbuf[256];          /* workspace for accumulating packet */
  67
  68 } gif_dest_struct;
  69
  70 typedef gif_dest_struct * gif_dest_ptr;
  71
  72 /* Largest value that will fit in N bits */
  73 #define MAXCODE(n_bits) ((1 << (n_bits)) - 1)
  74
  75
  76 /*
  77  * Routines to package finished data bytes into GIF data blocks.
  78  * A data block consists of a count byte (1..255) and that many data bytes.
  79  */
  80
  81 LOCAL(void)
  82 flush_packet (gif_dest_ptr dinfo)
  83 /* flush any accumulated data */
  84 {
  85   if (dinfo->bytesinpkt > 0) {  /* never write zero-length packet */
  86     dinfo->packetbuf[0] = (char) dinfo->bytesinpkt++;
  87     if (JFWRITE(dinfo->pub.output_file, dinfo->packetbuf, dinfo->bytesinpkt)
  88         != (size_t) dinfo->bytesinpkt)
  89       ERREXIT(dinfo->cinfo, JERR_FILE_WRITE);
  90     dinfo->bytesinpkt = 0;
  91   }
  92 }
  93
  94
  95 /* Add a character to current packet; flush to disk if necessary */
  96 #define CHAR_OUT(dinfo,c)  \
  97         { (dinfo)->packetbuf[++(dinfo)->bytesinpkt] = (char) (c);  \
  98             if ((dinfo)->bytesinpkt >= 255)  \
  99               flush_packet(dinfo);  \
 100         }
 101
 102
 103 /* Routine to convert variable-width codes into a byte stream */
 104
 105 LOCAL(void)
 106 output (gif_dest_ptr dinfo, int code)
 107 /* Emit a code of n_bits bits */
 108 /* Uses cur_accum and cur_bits to reblock into 8-bit bytes */
 109 {
 110   dinfo->cur_accum |= ((INT32) code) << dinfo->cur_bits;
 111   dinfo->cur_bits += dinfo->n_bits;
 112
 113   while (dinfo->cur_bits >= 8) {
 114     CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF);
 115     dinfo->cur_accum >>= 8;
 116     dinfo->cur_bits -= 8;
 117   }
 118 }
 119
 120
 121 /* The pseudo-compression algorithm.
 122  *
 123  * In this module we simply output each pixel value as a separate symbol;
 124  * thus, no compression occurs.  In fact, there is expansion of one bit per
 125  * pixel, because we use a symbol width one bit wider than the pixel width.
 126  *
 127  * GIF ordinarily uses variable-width symbols, and the decoder will expect
 128  * to ratchet up the symbol width after a fixed number of symbols.
 129  * To simplify the logic and keep the expansion penalty down, we emit a
 130  * GIF Clear code to reset the decoder just before the width would ratchet up.
 131  * Thus, all the symbols in the output file will have the same bit width.
 132  * Note that emitting the Clear codes at the right times is a mere matter of
 133  * counting output symbols and is in no way dependent on the LZW patent.
 134  *
 135  * With a small basic pixel width (low color count), Clear codes will be
 136  * needed very frequently, causing the file to expand even more.  So this
 137  * simplistic approach wouldn't work too well on bilevel images, for example.
 138  * But for output of JPEG conversions the pixel width will usually be 8 bits
 139  * (129 to 256 colors), so the overhead added by Clear symbols is only about
 140  * one symbol in every 256.
 141  */
 142
 143 LOCAL(void)
 144 compress_init (gif_dest_ptr dinfo, int i_bits)
 145 /* Initialize pseudo-compressor */
 146 {
 147   /* init all the state variables */
 148   dinfo->n_bits = i_bits;
 149   dinfo->maxcode = MAXCODE(dinfo->n_bits);
 150   dinfo->ClearCode = (1 << (i_bits - 1));
 151   dinfo->EOFCode = dinfo->ClearCode + 1;
 152   dinfo->code_counter = dinfo->ClearCode + 2;
 153   /* init output buffering vars */
 154   dinfo->bytesinpkt = 0;
 155   dinfo->cur_accum = 0;
 156   dinfo->cur_bits = 0;
 157   /* GIF specifies an initial Clear code */
 158   output(dinfo, dinfo->ClearCode);
 159 }
 160
 161
 162 LOCAL(void)
 163 compress_pixel (gif_dest_ptr dinfo, int c)
 164 /* Accept and "compress" one pixel value.
 165  * The given value must be less than n_bits wide.
 166  */
 167 {
 168   /* Output the given pixel value as a symbol. */
 169   output(dinfo, c);
 170   /* Issue Clear codes often enough to keep the reader from ratcheting up
 171    * its symbol size.
 172    */
 173   if (dinfo->code_counter < dinfo->maxcode) {
 174     dinfo->code_counter++;
 175   } else {
 176     output(dinfo, dinfo->ClearCode);
 177     dinfo->code_counter = dinfo->ClearCode + 2; /* reset the counter */
 178   }
 179 }
 180
 181
 182 LOCAL(void)
 183 compress_term (gif_dest_ptr dinfo)
 184 /* Clean up at end */
 185 {
 186   /* Send an EOF code */
 187   output(dinfo, dinfo->EOFCode);
 188   /* Flush the bit-packing buffer */
 189   if (dinfo->cur_bits > 0) {
 190     CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF);
 191   }
 192   /* Flush the packet buffer */
 193   flush_packet(dinfo);
 194 }
 195
 196
 197 /* GIF header construction */
 198
 199
 200 LOCAL(void)
 201 put_word (gif_dest_ptr dinfo, unsigned int w)
 202 /* Emit a 16-bit word, LSB first */
 203 {
 204   putc(w & 0xFF, dinfo->pub.output_file);
 205   putc((w >> 8) & 0xFF, dinfo->pub.output_file);
 206 }
 207
 208
 209 LOCAL(void)
 210 put_3bytes (gif_dest_ptr dinfo, int val)
 211 /* Emit 3 copies of same byte value --- handy subr for colormap construction */
 212 {
 213   putc(val, dinfo->pub.output_file);
 214   putc(val, dinfo->pub.output_file);
 215   putc(val, dinfo->pub.output_file);
 216 }
 217
 218
 219 LOCAL(void)
 220 emit_header (gif_dest_ptr dinfo, int num_colors, JSAMPARRAY colormap)
 221 /* Output the GIF file header, including color map */
 222 /* If colormap==NULL, synthesize a grayscale colormap */
 223 {
 224   int BitsPerPixel, ColorMapSize, InitCodeSize, FlagByte;
 225   int cshift = dinfo->cinfo->data_precision - 8;
 226   int i;
 227
 228   if (num_colors > 256)
 229     ERREXIT1(dinfo->cinfo, JERR_TOO_MANY_COLORS, num_colors);
 230   /* Compute bits/pixel and related values */
 231   BitsPerPixel = 1;
 232   while (num_colors > (1 << BitsPerPixel))
 233     BitsPerPixel++;
 234   ColorMapSize = 1 << BitsPerPixel;
 235   if (BitsPerPixel <= 1)
 236     InitCodeSize = 2;
 237   else
 238     InitCodeSize = BitsPerPixel;
 239   /*
 240    * Write the GIF header.
 241    * Note that we generate a plain GIF87 header for maximum compatibility.
 242    */
 243   putc('G', dinfo->pub.output_file);
 244   putc('I', dinfo->pub.output_file);
 245   putc('F', dinfo->pub.output_file);
 246   putc('8', dinfo->pub.output_file);
 247   putc('7', dinfo->pub.output_file);
 248   putc('a', dinfo->pub.output_file);
 249   /* Write the Logical Screen Descriptor */
 250   put_word(dinfo, (unsigned int) dinfo->cinfo->output_width);
 251   put_word(dinfo, (unsigned int) dinfo->cinfo->output_height);
 252   FlagByte = 0x80;              /* Yes, there is a global color table */
 253   FlagByte |= (BitsPerPixel-1) << 4; /* color resolution */
 254   FlagByte |= (BitsPerPixel-1); /* size of global color table */
 255   putc(FlagByte, dinfo->pub.output_file);
 256   putc(0, dinfo->pub.output_file); /* Background color index */
 257   putc(0, dinfo->pub.output_file); /* Reserved (aspect ratio in GIF89) */
 258   /* Write the Global Color Map */
 259   /* If the color map is more than 8 bits precision, */
 260   /* we reduce it to 8 bits by shifting */
 261   for (i=0; i < ColorMapSize; i++) {
 262     if (i < num_colors) {
 263       if (colormap != NULL) {
 264         if (dinfo->cinfo->out_color_space == JCS_RGB) {
 265           /* Normal case: RGB color map */
 266           putc(GETJSAMPLE(colormap[0][i]) >> cshift, dinfo->pub.output_file);
 267           putc(GETJSAMPLE(colormap[1][i]) >> cshift, dinfo->pub.output_file);
 268           putc(GETJSAMPLE(colormap[2][i]) >> cshift, dinfo->pub.output_file);
 269         } else {
 270           /* Grayscale "color map": possible if quantizing grayscale image */
 271           put_3bytes(dinfo, GETJSAMPLE(colormap[0][i]) >> cshift);
 272         }
 273       } else {
 274         /* Create a grayscale map of num_colors values, range 0..255 */
 275         put_3bytes(dinfo, (i * 255 + (num_colors-1)/2) / (num_colors-1));
 276       }
 277     } else {
 278       /* fill out the map to a power of 2 */
 279       put_3bytes(dinfo, 0);
 280     }
 281   }
 282   /* Write image separator and Image Descriptor */
 283   putc(',', dinfo->pub.output_file); /* separator */
 284   put_word(dinfo, 0);           /* left/top offset */
 285   put_word(dinfo, 0);
 286   put_word(dinfo, (unsigned int) dinfo->cinfo->output_width); /* image size */
 287   put_word(dinfo, (unsigned int) dinfo->cinfo->output_height);
 288   /* flag byte: not interlaced, no local color map */
 289   putc(0x00, dinfo->pub.output_file);
 290   /* Write Initial Code Size byte */
 291   putc(InitCodeSize, dinfo->pub.output_file);
 292
 293   /* Initialize for "compression" of image data */
 294   compress_init(dinfo, InitCodeSize+1);
 295 }
 296
 297
 298 /*
 299  * Startup: write the file header.
 300  */
 301
 302 METHODDEF(void)
 303 start_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
 304 {
 305   gif_dest_ptr dest = (gif_dest_ptr) dinfo;
 306
 307   if (cinfo->quantize_colors)
 308     emit_header(dest, cinfo->actual_number_of_colors, cinfo->colormap);
 309   else
 310     emit_header(dest, 256, (JSAMPARRAY) NULL);
 311 }
 312
 313
 314 /*
 315  * Write some pixel data.
 316  * In this module rows_supplied will always be 1.
 317  */
 318
 319 METHODDEF(void)
 320 put_pixel_rows (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo,
 321                 JDIMENSION rows_supplied)
 322 {
 323   gif_dest_ptr dest = (gif_dest_ptr) dinfo;
 324   register JSAMPROW ptr;
 325   register JDIMENSION col;
 326
 327   ptr = dest->pub.buffer[0];
 328   for (col = cinfo->output_width; col > 0; col--) {
 329     compress_pixel(dest, GETJSAMPLE(*ptr++));
 330   }
 331 }
 332
 333
 334 /*
 335  * Finish up at the end of the file.
 336  */
 337
 338 METHODDEF(void)
 339 finish_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
 340 {
 341   gif_dest_ptr dest = (gif_dest_ptr) dinfo;
 342
 343   /* Flush "compression" mechanism */
 344   compress_term(dest);
 345   /* Write a zero-length data block to end the series */
 346   putc(0, dest->pub.output_file);
 347   /* Write the GIF terminator mark */
 348   putc(';', dest->pub.output_file);
 349   /* Make sure we wrote the output file OK */
 350   fflush(dest->pub.output_file);
 351   if (ferror(dest->pub.output_file))
 352     ERREXIT(cinfo, JERR_FILE_WRITE);
 353 }
 354
 355
 356 /*
 357  * The module selection routine for GIF format output.
 358  */
 359
 360 GLOBAL(djpeg_dest_ptr)
 361 jinit_write_gif (j_decompress_ptr cinfo)
 362 {
 363   gif_dest_ptr dest;
 364
 365   /* Create module interface object, fill in method pointers */
 366   dest = (gif_dest_ptr)
 367       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 368                                   SIZEOF(gif_dest_struct));
 369   dest->cinfo = cinfo;          /* make back link for subroutines */
 370   dest->pub.start_output = start_output_gif;
 371   dest->pub.put_pixel_rows = put_pixel_rows;
 372   dest->pub.finish_output = finish_output_gif;
 373
 374   if (cinfo->out_color_space != JCS_GRAYSCALE &&
 375       cinfo->out_color_space != JCS_RGB)
 376     ERREXIT(cinfo, JERR_GIF_COLORSPACE);
 377
 378   /* Force quantization if color or if > 8 bits input */
 379   if (cinfo->out_color_space != JCS_GRAYSCALE || cinfo->data_precision > 8) {
 380     /* Force quantization to at most 256 colors */
 381     cinfo->quantize_colors = TRUE;
 382     if (cinfo->desired_number_of_colors > 256)
 383       cinfo->desired_number_of_colors = 256;
 384   }
 385
 386   /* Calculate output image dimensions so we can allocate space */
 387   jpeg_calc_output_dimensions(cinfo);
 388
 389   if (cinfo->output_components != 1) /* safety check: just one component? */
 390     ERREXIT(cinfo, JERR_GIF_BUG);
 391
 392   /* Create decompressor output buffer. */
 393   dest->pub.buffer = (*cinfo->mem->alloc_sarray)
 394     ((j_common_ptr) cinfo, JPOOL_IMAGE, cinfo->output_width, (JDIMENSION) 1);
 395   dest->pub.buffer_height = 1;
 396
 397   return &dest->pub;
 398 }
 399
 400 #endif /* GIF_SUPPORTED */