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+/*
+ * 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>.
+ * 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 */
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