workbench/libs/jpeg/wrgif.c

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