/*

 * wrgif.c

 *

 * Copyright (C) 1991-1997, Thomas G. Lane.

 * This file is part of the Independent JPEG Group's software.

 * For conditions of distribution and use, see the accompanying README file.

 *

 * This file contains routines to write output images in GIF format.

 *

 **************************************************************************

 * NOTE: to avoid entanglements with Unisys' patent on LZW compression,   *

 * this code has been modified to output "uncompressed GIF" files.        *

 * There is no trace of the LZW algorithm in this file.                   *

 **************************************************************************

 *

 * These routines may need modification for non-Unix environments or

 * specialized applications.  As they stand, they assume output to

 * an ordinary stdio stream.

 */

/*

 * This code is loosely based on ppmtogif from the PBMPLUS distribution

 * of Feb. 1991.  That file contains the following copyright notice:

 *    Based on GIFENCODE by David Rowley <mgardi@watdscu.waterloo.edu>.</mgardi@watdscu.waterloo.edu>

 *    Lempel-Ziv compression based on "compress" by Spencer W. Thomas et al.

 *    Copyright (C) 1989 by Jef Poskanzer.

 *    Permission to use, copy, modify, and distribute this software and its

 *    documentation for any purpose and without fee is hereby granted, provided

 *    that the above copyright notice appear in all copies and that both that

 *    copyright notice and this permission notice appear in supporting

 *    documentation.  This software is provided "as is" without express or

 *    implied warranty.

 *

 * We are also required to state that

 *    "The Graphics Interchange Format(c) is the Copyright property of

 *    CompuServe Incorporated. GIF(sm) is a Service Mark property of

 *    CompuServe Incorporated."

 */

#include "cdjpeg.h"		/* Common decls for cjpeg/djpeg applications */

#ifdef GIF_SUPPORTED

/* Private version of data destination object */

typedef struct {

  struct djpeg_dest_struct pub;	/* public fields */

  j_decompress_ptr cinfo;	/* back link saves passing separate parm */

  /* State for packing variable-width codes into a bitstream */

  int n_bits;			/* current number of bits/code */

  int maxcode;			/* maximum code, given n_bits */

  INT32 cur_accum;		/* holds bits not yet output */

  int cur_bits;			/* # of bits in cur_accum */

  /* State for GIF code assignment */

  int ClearCode;		/* clear code (doesn't change) */

  int EOFCode;			/* EOF code (ditto) */

  int code_counter;		/* counts output symbols */

  /* GIF data packet construction buffer */

  int bytesinpkt;		/* # of bytes in current packet */

  char packetbuf[256];		/* workspace for accumulating packet */

} gif_dest_struct;

typedef gif_dest_struct * gif_dest_ptr;

/* Largest value that will fit in N bits */

#define MAXCODE(n_bits)	((1 << (n_bits)) - 1)

/*

 * Routines to package finished data bytes into GIF data blocks.

 * A data block consists of a count byte (1..255) and that many data bytes.

 */

LOCAL(void)

flush_packet (gif_dest_ptr dinfo)

/* flush any accumulated data */

{

  if (dinfo->bytesinpkt > 0) {	/* never write zero-length packet */

    dinfo->packetbuf[0] = (char) dinfo->bytesinpkt++;

    if (JFWRITE(dinfo->pub.output_file, dinfo->packetbuf, dinfo->bytesinpkt)

	!= (size_t) dinfo->bytesinpkt)

      ERREXIT(dinfo->cinfo, JERR_FILE_WRITE);

    dinfo->bytesinpkt = 0;

  }

}

/* Add a character to current packet; flush to disk if necessary */

#define CHAR_OUT(dinfo,c)  \

	{ (dinfo)->packetbuf[++(dinfo)->bytesinpkt] = (char) (c);  \

	    if ((dinfo)->bytesinpkt >= 255)  \

	      flush_packet(dinfo);  \

	}

/* Routine to convert variable-width codes into a byte stream */

LOCAL(void)

output (gif_dest_ptr dinfo, int code)

/* Emit a code of n_bits bits */

/* Uses cur_accum and cur_bits to reblock into 8-bit bytes */

{

  dinfo->cur_accum |= ((INT32) code) << dinfo->cur_bits;

  dinfo->cur_bits += dinfo->n_bits;

  while (dinfo->cur_bits >= 8) {

    CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF);

    dinfo->cur_accum >>= 8;

    dinfo->cur_bits -= 8;

  }

}

/* The pseudo-compression algorithm.

 *

 * In this module we simply output each pixel value as a separate symbol;

 * thus, no compression occurs.  In fact, there is expansion of one bit per

 * pixel, because we use a symbol width one bit wider than the pixel width.

 *

 * GIF ordinarily uses variable-width symbols, and the decoder will expect

 * to ratchet up the symbol width after a fixed number of symbols.

 * To simplify the logic and keep the expansion penalty down, we emit a

 * GIF Clear code to reset the decoder just before the width would ratchet up.

 * Thus, all the symbols in the output file will have the same bit width.

 * Note that emitting the Clear codes at the right times is a mere matter of

 * counting output symbols and is in no way dependent on the LZW patent.

 *

 * With a small basic pixel width (low color count), Clear codes will be

 * needed very frequently, causing the file to expand even more.  So this

 * simplistic approach wouldn't work too well on bilevel images, for example.

 * But for output of JPEG conversions the pixel width will usually be 8 bits

 * (129 to 256 colors), so the overhead added by Clear symbols is only about

 * one symbol in every 256.

 */

LOCAL(void)

compress_init (gif_dest_ptr dinfo, int i_bits)

/* Initialize pseudo-compressor */

{

  /* init all the state variables */

  dinfo->n_bits = i_bits;

  dinfo->maxcode = MAXCODE(dinfo->n_bits);

  dinfo->ClearCode = (1 << (i_bits - 1));

  dinfo->EOFCode = dinfo->ClearCode + 1;

  dinfo->code_counter = dinfo->ClearCode + 2;

  /* init output buffering vars */

  dinfo->bytesinpkt = 0;

  dinfo->cur_accum = 0;

  dinfo->cur_bits = 0;

  /* GIF specifies an initial Clear code */

  output(dinfo, dinfo->ClearCode);

}

LOCAL(void)

compress_pixel (gif_dest_ptr dinfo, int c)

/* Accept and "compress" one pixel value.

 * The given value must be less than n_bits wide.

 */

{

  /* Output the given pixel value as a symbol. */

  output(dinfo, c);

  /* Issue Clear codes often enough to keep the reader from ratcheting up

   * its symbol size.

   */

  if (dinfo->code_counter < dinfo->maxcode) {

    dinfo->code_counter++;

  } else {

    output(dinfo, dinfo->ClearCode);

    dinfo->code_counter = dinfo->ClearCode + 2;	/* reset the counter */

  }

}

LOCAL(void)

compress_term (gif_dest_ptr dinfo)

/* Clean up at end */

{

  /* Send an EOF code */

  output(dinfo, dinfo->EOFCode);

  /* Flush the bit-packing buffer */

  if (dinfo->cur_bits > 0) {

    CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF);

  }

  /* Flush the packet buffer */

  flush_packet(dinfo);

}

/* GIF header construction */

LOCAL(void)

put_word (gif_dest_ptr dinfo, unsigned int w)

/* Emit a 16-bit word, LSB first */

{

  putc(w & 0xFF, dinfo->pub.output_file);

  putc((w >> 8) & 0xFF, dinfo->pub.output_file);

}

LOCAL(void)

put_3bytes (gif_dest_ptr dinfo, int val)

/* Emit 3 copies of same byte value --- handy subr for colormap construction */

{

  putc(val, dinfo->pub.output_file);

  putc(val, dinfo->pub.output_file);

  putc(val, dinfo->pub.output_file);

}

LOCAL(void)

emit_header (gif_dest_ptr dinfo, int num_colors, JSAMPARRAY colormap)

/* Output the GIF file header, including color map */

/* If colormap==NULL, synthesize a gray-scale colormap */

{

  int BitsPerPixel, ColorMapSize, InitCodeSize, FlagByte;

  int cshift = dinfo->cinfo->data_precision - 8;

  int i;

  if (num_colors > 256)

    ERREXIT1(dinfo->cinfo, JERR_TOO_MANY_COLORS, num_colors);

  /* Compute bits/pixel and related values */

  BitsPerPixel = 1;

  while (num_colors > (1 << BitsPerPixel))

    BitsPerPixel++;

  ColorMapSize = 1 << BitsPerPixel;

  if (BitsPerPixel <= 1)

    InitCodeSize = 2;

  else

    InitCodeSize = BitsPerPixel;

  /*

   * Write the GIF header.

   * Note that we generate a plain GIF87 header for maximum compatibility.

   */

  putc('G', dinfo->pub.output_file);

  putc('I', dinfo->pub.output_file);

  putc('F', dinfo->pub.output_file);

  putc('8', dinfo->pub.output_file);

  putc('7', dinfo->pub.output_file);

  putc('a', dinfo->pub.output_file);

  /* Write the Logical Screen Descriptor */

  put_word(dinfo, (unsigned int) dinfo->cinfo->output_width);

  put_word(dinfo, (unsigned int) dinfo->cinfo->output_height);

  FlagByte = 0x80;		/* Yes, there is a global color table */

  FlagByte |= (BitsPerPixel-1) << 4; /* color resolution */

  FlagByte |= (BitsPerPixel-1);	/* size of global color table */

  putc(FlagByte, dinfo->pub.output_file);

  putc(0, dinfo->pub.output_file); /* Background color index */

  putc(0, dinfo->pub.output_file); /* Reserved (aspect ratio in GIF89) */

  /* Write the Global Color Map */

  /* If the color map is more than 8 bits precision, */

  /* we reduce it to 8 bits by shifting */

  for (i=0; i < ColorMapSize; i++) {

    if (i < num_colors) {

      if (colormap != NULL) {

	if (dinfo->cinfo->out_color_space == JCS_RGB) {

	  /* Normal case: RGB color map */

	  putc(GETJSAMPLE(colormap[0][i]) >> cshift, dinfo->pub.output_file);

	  putc(GETJSAMPLE(colormap[1][i]) >> cshift, dinfo->pub.output_file);

	  putc(GETJSAMPLE(colormap[2][i]) >> cshift, dinfo->pub.output_file);

	} else {

	  /* Grayscale "color map": possible if quantizing grayscale image */

	  put_3bytes(dinfo, GETJSAMPLE(colormap[0][i]) >> cshift);

	}

      } else {

	/* Create a gray-scale map of num_colors values, range 0..255 */

	put_3bytes(dinfo, (i * 255 + (num_colors-1)/2) / (num_colors-1));

      }

    } else {

      /* fill out the map to a power of 2 */

      put_3bytes(dinfo, 0);

    }

  }

  /* Write image separator and Image Descriptor */

  putc(',', dinfo->pub.output_file); /* separator */

  put_word(dinfo, 0);		/* left/top offset */

  put_word(dinfo, 0);

  put_word(dinfo, (unsigned int) dinfo->cinfo->output_width); /* image size */

  put_word(dinfo, (unsigned int) dinfo->cinfo->output_height);

  /* flag byte: not interlaced, no local color map */

  putc(0x00, dinfo->pub.output_file);

  /* Write Initial Code Size byte */

  putc(InitCodeSize, dinfo->pub.output_file);

  /* Initialize for "compression" of image data */

  compress_init(dinfo, InitCodeSize+1);

}

/*

 * Startup: write the file header.

 */

METHODDEF(void)

start_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)

{

  gif_dest_ptr dest = (gif_dest_ptr) dinfo;

  if (cinfo->quantize_colors)

    emit_header(dest, cinfo->actual_number_of_colors, cinfo->colormap);

  else

    emit_header(dest, 256, (JSAMPARRAY) NULL);

}

/*

 * Write some pixel data.

 * In this module rows_supplied will always be 1.

 */

METHODDEF(void)

put_pixel_rows (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo,

		JDIMENSION rows_supplied)

{

  gif_dest_ptr dest = (gif_dest_ptr) dinfo;

  register JSAMPROW ptr;

  register JDIMENSION col;

  ptr = dest->pub.buffer[0];

  for (col = cinfo->output_width; col > 0; col--) {

    compress_pixel(dest, GETJSAMPLE(*ptr++));

  }

}

/*

 * Finish up at the end of the file.

 */

METHODDEF(void)

finish_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)

{

  gif_dest_ptr dest = (gif_dest_ptr) dinfo;

  /* Flush "compression" mechanism */

  compress_term(dest);

  /* Write a zero-length data block to end the series */

  putc(0, dest->pub.output_file);

  /* Write the GIF terminator mark */

  putc(';', dest->pub.output_file);

  /* Make sure we wrote the output file OK */

  fflush(dest->pub.output_file);

  if (ferror(dest->pub.output_file))

    ERREXIT(cinfo, JERR_FILE_WRITE);

}

/*

 * The module selection routine for GIF format output.

 */

GLOBAL(djpeg_dest_ptr)

jinit_write_gif (j_decompress_ptr cinfo)

{

  gif_dest_ptr dest;

  /* Create module interface object, fill in method pointers */

  dest = (gif_dest_ptr)

      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

				  SIZEOF(gif_dest_struct));

  dest->cinfo = cinfo;		/* make back link for subroutines */

  dest->pub.start_output = start_output_gif;

  dest->pub.put_pixel_rows = put_pixel_rows;

  dest->pub.finish_output = finish_output_gif;

  if (cinfo->out_color_space != JCS_GRAYSCALE &&

      cinfo->out_color_space != JCS_RGB)

    ERREXIT(cinfo, JERR_GIF_COLORSPACE);

  /* Force quantization if color or if > 8 bits input */

  if (cinfo->out_color_space != JCS_GRAYSCALE || cinfo->data_precision > 8) {

    /* Force quantization to at most 256 colors */

    cinfo->quantize_colors = TRUE;

    if (cinfo->desired_number_of_colors > 256)

      cinfo->desired_number_of_colors = 256;

  }

  /* Calculate output image dimensions so we can allocate space */

  jpeg_calc_output_dimensions(cinfo);

  if (cinfo->output_components != 1) /* safety check: just one component? */

    ERREXIT(cinfo, JERR_GIF_BUG);

  /* Create decompressor output buffer. */

  dest->pub.buffer = (*cinfo->mem->alloc_sarray)

    ((j_common_ptr) cinfo, JPOOL_IMAGE, cinfo->output_width, (JDIMENSION) 1);

  dest->pub.buffer_height = 1;

  return (djpeg_dest_ptr) dest;

}

#endif /* GIF_SUPPORTED */