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* Copyright (C) 1991-1997, Thomas G. Lane.
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* This file is part of the Independent JPEG Group's software.
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* For conditions of distribution and use, see the accompanying README file.
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* This file contains routines to write output images in GIF format.
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**************************************************************************
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* NOTE: to avoid entanglements with Unisys' patent on LZW compression, *
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* this code has been modified to output "uncompressed GIF" files. *
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* There is no trace of the LZW algorithm in this file. *
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**************************************************************************
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* These routines may need modification for non-Unix environments or
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* specialized applications. As they stand, they assume output to
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* an ordinary stdio stream.
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* This code is loosely based on ppmtogif from the PBMPLUS distribution
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* of Feb. 1991. That file contains the following copyright notice:
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* Based on GIFENCODE by David Rowley <mgardi@watdscu.waterloo.edu>.
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* Lempel-Ziv compression based on "compress" by Spencer W. Thomas et al.
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* Copyright (C) 1989 by Jef Poskanzer.
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* Permission to use, copy, modify, and distribute this software and its
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* documentation for any purpose and without fee is hereby granted, provided
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* that the above copyright notice appear in all copies and that both that
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* copyright notice and this permission notice appear in supporting
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* documentation. This software is provided "as is" without express or
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* We are also required to state that
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* "The Graphics Interchange Format(c) is the Copyright property of
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* CompuServe Incorporated. GIF(sm) is a Service Mark property of
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* CompuServe Incorporated."
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#include "cdjpeg.h" /* Common decls for cjpeg/djpeg applications */
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/* Private version of data destination object */
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struct djpeg_dest_struct pub; /* public fields */
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j_decompress_ptr cinfo; /* back link saves passing separate parm */
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/* State for packing variable-width codes into a bitstream */
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int n_bits; /* current number of bits/code */
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int maxcode; /* maximum code, given n_bits */
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INT32 cur_accum; /* holds bits not yet output */
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int cur_bits; /* # of bits in cur_accum */
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/* State for GIF code assignment */
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int ClearCode; /* clear code (doesn't change) */
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int EOFCode; /* EOF code (ditto) */
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int code_counter; /* counts output symbols */
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/* GIF data packet construction buffer */
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int bytesinpkt; /* # of bytes in current packet */
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char packetbuf[256]; /* workspace for accumulating packet */
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typedef gif_dest_struct * gif_dest_ptr;
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/* Largest value that will fit in N bits */
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#define MAXCODE(n_bits) ((1 << (n_bits)) - 1)
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* Routines to package finished data bytes into GIF data blocks.
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* A data block consists of a count byte (1..255) and that many data bytes.
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flush_packet (gif_dest_ptr dinfo)
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/* flush any accumulated data */
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if (dinfo->bytesinpkt > 0) { /* never write zero-length packet */
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dinfo->packetbuf[0] = (char) dinfo->bytesinpkt++;
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if (JFWRITE(dinfo->pub.output_file, dinfo->packetbuf, dinfo->bytesinpkt)
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!= (size_t) dinfo->bytesinpkt)
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ERREXIT(dinfo->cinfo, JERR_FILE_WRITE);
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dinfo->bytesinpkt = 0;
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/* Add a character to current packet; flush to disk if necessary */
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#define CHAR_OUT(dinfo,c) \
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{ (dinfo)->packetbuf[++(dinfo)->bytesinpkt] = (char) (c); \
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if ((dinfo)->bytesinpkt >= 255) \
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flush_packet(dinfo); \
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/* Routine to convert variable-width codes into a byte stream */
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output (gif_dest_ptr dinfo, int code)
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/* Emit a code of n_bits bits */
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/* Uses cur_accum and cur_bits to reblock into 8-bit bytes */
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dinfo->cur_accum |= ((INT32) code) << dinfo->cur_bits;
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dinfo->cur_bits += dinfo->n_bits;
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while (dinfo->cur_bits >= 8) {
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CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF);
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dinfo->cur_accum >>= 8;
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dinfo->cur_bits -= 8;
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/* The pseudo-compression algorithm.
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* In this module we simply output each pixel value as a separate symbol;
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* thus, no compression occurs. In fact, there is expansion of one bit per
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* pixel, because we use a symbol width one bit wider than the pixel width.
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* GIF ordinarily uses variable-width symbols, and the decoder will expect
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* to ratchet up the symbol width after a fixed number of symbols.
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* To simplify the logic and keep the expansion penalty down, we emit a
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* GIF Clear code to reset the decoder just before the width would ratchet up.
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* Thus, all the symbols in the output file will have the same bit width.
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* Note that emitting the Clear codes at the right times is a mere matter of
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* counting output symbols and is in no way dependent on the LZW patent.
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* With a small basic pixel width (low color count), Clear codes will be
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* needed very frequently, causing the file to expand even more. So this
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* simplistic approach wouldn't work too well on bilevel images, for example.
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* But for output of JPEG conversions the pixel width will usually be 8 bits
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* (129 to 256 colors), so the overhead added by Clear symbols is only about
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* one symbol in every 256.
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compress_init (gif_dest_ptr dinfo, int i_bits)
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/* Initialize pseudo-compressor */
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/* init all the state variables */
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dinfo->n_bits = i_bits;
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dinfo->maxcode = MAXCODE(dinfo->n_bits);
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dinfo->ClearCode = (1 << (i_bits - 1));
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dinfo->EOFCode = dinfo->ClearCode + 1;
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dinfo->code_counter = dinfo->ClearCode + 2;
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/* init output buffering vars */
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dinfo->bytesinpkt = 0;
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dinfo->cur_accum = 0;
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/* GIF specifies an initial Clear code */
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output(dinfo, dinfo->ClearCode);
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compress_pixel (gif_dest_ptr dinfo, int c)
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/* Accept and "compress" one pixel value.
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* The given value must be less than n_bits wide.
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/* Output the given pixel value as a symbol. */
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/* Issue Clear codes often enough to keep the reader from ratcheting up
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if (dinfo->code_counter < dinfo->maxcode) {
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dinfo->code_counter++;
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output(dinfo, dinfo->ClearCode);
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dinfo->code_counter = dinfo->ClearCode + 2; /* reset the counter */
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compress_term (gif_dest_ptr dinfo)
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/* Clean up at end */
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/* Send an EOF code */
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output(dinfo, dinfo->EOFCode);
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/* Flush the bit-packing buffer */
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if (dinfo->cur_bits > 0) {
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CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF);
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/* Flush the packet buffer */
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/* GIF header construction */
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put_word (gif_dest_ptr dinfo, unsigned int w)
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/* Emit a 16-bit word, LSB first */
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putc(w & 0xFF, dinfo->pub.output_file);
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putc((w >> 8) & 0xFF, dinfo->pub.output_file);
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put_3bytes (gif_dest_ptr dinfo, int val)
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/* Emit 3 copies of same byte value --- handy subr for colormap construction */
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putc(val, dinfo->pub.output_file);
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putc(val, dinfo->pub.output_file);
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putc(val, dinfo->pub.output_file);
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emit_header (gif_dest_ptr dinfo, int num_colors, JSAMPARRAY colormap)
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/* Output the GIF file header, including color map */
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/* If colormap==NULL, synthesize a gray-scale colormap */
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int BitsPerPixel, ColorMapSize, InitCodeSize, FlagByte;
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int cshift = dinfo->cinfo->data_precision - 8;
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if (num_colors > 256)
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ERREXIT1(dinfo->cinfo, JERR_TOO_MANY_COLORS, num_colors);
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/* Compute bits/pixel and related values */
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while (num_colors > (1 << BitsPerPixel))
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ColorMapSize = 1 << BitsPerPixel;
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if (BitsPerPixel <= 1)
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InitCodeSize = BitsPerPixel;
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* Write the GIF header.
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* Note that we generate a plain GIF87 header for maximum compatibility.
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putc('G', dinfo->pub.output_file);
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putc('I', dinfo->pub.output_file);
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putc('F', dinfo->pub.output_file);
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putc('8', dinfo->pub.output_file);
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putc('7', dinfo->pub.output_file);
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putc('a', dinfo->pub.output_file);
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/* Write the Logical Screen Descriptor */
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put_word(dinfo, (unsigned int) dinfo->cinfo->output_width);
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put_word(dinfo, (unsigned int) dinfo->cinfo->output_height);
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FlagByte = 0x80; /* Yes, there is a global color table */
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FlagByte |= (BitsPerPixel-1) << 4; /* color resolution */
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FlagByte |= (BitsPerPixel-1); /* size of global color table */
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putc(FlagByte, dinfo->pub.output_file);
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putc(0, dinfo->pub.output_file); /* Background color index */
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putc(0, dinfo->pub.output_file); /* Reserved (aspect ratio in GIF89) */
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/* Write the Global Color Map */
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/* If the color map is more than 8 bits precision, */
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/* we reduce it to 8 bits by shifting */
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for (i=0; i < ColorMapSize; i++) {
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if (i < num_colors) {
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if (colormap != NULL) {
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if (dinfo->cinfo->out_color_space == JCS_RGB) {
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/* Normal case: RGB color map */
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putc(GETJSAMPLE(colormap[0][i]) >> cshift, dinfo->pub.output_file);
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putc(GETJSAMPLE(colormap[1][i]) >> cshift, dinfo->pub.output_file);
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putc(GETJSAMPLE(colormap[2][i]) >> cshift, dinfo->pub.output_file);
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/* Grayscale "color map": possible if quantizing grayscale image */
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put_3bytes(dinfo, GETJSAMPLE(colormap[0][i]) >> cshift);
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/* Create a gray-scale map of num_colors values, range 0..255 */
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put_3bytes(dinfo, (i * 255 + (num_colors-1)/2) / (num_colors-1));
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/* fill out the map to a power of 2 */
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put_3bytes(dinfo, 0);
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/* Write image separator and Image Descriptor */
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putc(',', dinfo->pub.output_file); /* separator */
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put_word(dinfo, 0); /* left/top offset */
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put_word(dinfo, (unsigned int) dinfo->cinfo->output_width); /* image size */
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put_word(dinfo, (unsigned int) dinfo->cinfo->output_height);
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/* flag byte: not interlaced, no local color map */
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putc(0x00, dinfo->pub.output_file);
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/* Write Initial Code Size byte */
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putc(InitCodeSize, dinfo->pub.output_file);
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/* Initialize for "compression" of image data */
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compress_init(dinfo, InitCodeSize+1);
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* Startup: write the file header.
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start_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
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gif_dest_ptr dest = (gif_dest_ptr) dinfo;
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if (cinfo->quantize_colors)
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emit_header(dest, cinfo->actual_number_of_colors, cinfo->colormap);
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emit_header(dest, 256, (JSAMPARRAY) NULL);
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* Write some pixel data.
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* In this module rows_supplied will always be 1.
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put_pixel_rows (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo,
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JDIMENSION rows_supplied)
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gif_dest_ptr dest = (gif_dest_ptr) dinfo;
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register JSAMPROW ptr;
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register JDIMENSION col;
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ptr = dest->pub.buffer[0];
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for (col = cinfo->output_width; col > 0; col--) {
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compress_pixel(dest, GETJSAMPLE(*ptr++));
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* Finish up at the end of the file.
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finish_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
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gif_dest_ptr dest = (gif_dest_ptr) dinfo;
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/* Flush "compression" mechanism */
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/* Write a zero-length data block to end the series */
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putc(0, dest->pub.output_file);
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/* Write the GIF terminator mark */
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putc(';', dest->pub.output_file);
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/* Make sure we wrote the output file OK */
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fflush(dest->pub.output_file);
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if (ferror(dest->pub.output_file))
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ERREXIT(cinfo, JERR_FILE_WRITE);
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* The module selection routine for GIF format output.
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GLOBAL(djpeg_dest_ptr)
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jinit_write_gif (j_decompress_ptr cinfo)
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/* Create module interface object, fill in method pointers */
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dest = (gif_dest_ptr)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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SIZEOF(gif_dest_struct));
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dest->cinfo = cinfo; /* make back link for subroutines */
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dest->pub.start_output = start_output_gif;
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dest->pub.put_pixel_rows = put_pixel_rows;
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dest->pub.finish_output = finish_output_gif;
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if (cinfo->out_color_space != JCS_GRAYSCALE &&
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cinfo->out_color_space != JCS_RGB)
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ERREXIT(cinfo, JERR_GIF_COLORSPACE);
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/* Force quantization if color or if > 8 bits input */
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if (cinfo->out_color_space != JCS_GRAYSCALE || cinfo->data_precision > 8) {
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/* Force quantization to at most 256 colors */
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cinfo->quantize_colors = TRUE;
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if (cinfo->desired_number_of_colors > 256)
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cinfo->desired_number_of_colors = 256;
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/* Calculate output image dimensions so we can allocate space */
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jpeg_calc_output_dimensions(cinfo);
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if (cinfo->output_components != 1) /* safety check: just one component? */
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ERREXIT(cinfo, JERR_GIF_BUG);
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/* Create decompressor output buffer. */
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dest->pub.buffer = (*cinfo->mem->alloc_sarray)
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((j_common_ptr) cinfo, JPOOL_IMAGE, cinfo->output_width, (JDIMENSION) 1);
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dest->pub.buffer_height = 1;
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return (djpeg_dest_ptr) dest;
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#endif /* GIF_SUPPORTED */
added
removed
source/Irrlicht/jpeglib/wrgif.c
