ref: 556618eb07d1ac6e2c629a60acd53c45d53261be
dir: /sys/src/cmd/gs/jpeg/wrgif.c/
/* * 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 */