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https://git.code.sf.net/p/libpng/code.git
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281 lines
8.5 KiB
C
281 lines
8.5 KiB
C
/*---------------------------------------------------------------------------
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rpng - simple PNG display program readpng.c
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---------------------------------------------------------------------------
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Copyright (c) 1998-2000 Greg Roelofs. All rights reserved.
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This software is provided "as is," without warranty of any kind,
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express or implied. In no event shall the author or contributors
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be held liable for any damages arising in any way from the use of
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this software.
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Permission is granted to anyone to use this software for any purpose,
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including commercial applications, and to alter it and redistribute
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it freely, subject to the following restrictions:
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1. Redistributions of source code must retain the above copyright
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notice, disclaimer, and this list of conditions.
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2. Redistributions in binary form must reproduce the above copyright
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notice, disclaimer, and this list of conditions in the documenta-
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tion and/or other materials provided with the distribution.
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3. All advertising materials mentioning features or use of this
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software must display the following acknowledgment:
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This product includes software developed by Greg Roelofs
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and contributors for the book, "PNG: The Definitive Guide,"
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published by O'Reilly and Associates.
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---------------------------------------------------------------------------*/
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#include <stdio.h>
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#include <stdlib.h>
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#include "png.h" /* libpng header; includes zlib.h */
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#include "readpng.h" /* typedefs, common macros, public prototypes */
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/* future versions of libpng will provide this macro: */
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#ifndef png_jmpbuf
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# define png_jmpbuf(png_ptr) ((png_ptr)->jmpbuf)
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#endif
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static png_structp png_ptr = NULL;
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static png_infop info_ptr = NULL;
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png_uint_32 width, height;
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int bit_depth, color_type;
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uch *image_data = NULL;
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void readpng_version_info(void)
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{
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fprintf(stderr, " Compiled with libpng %s; using libpng %s.\n",
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PNG_LIBPNG_VER_STRING, png_libpng_ver);
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fprintf(stderr, " Compiled with zlib %s; using zlib %s.\n",
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ZLIB_VERSION, zlib_version);
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}
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/* return value = 0 for success, 1 for bad sig, 2 for bad IHDR, 4 for no mem */
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int readpng_init(FILE *infile, ulg *pWidth, ulg *pHeight)
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{
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uch sig[8];
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/* first do a quick check that the file really is a PNG image; could
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* have used slightly more general png_sig_cmp() function instead */
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fread(sig, 1, 8, infile);
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if (!png_check_sig(sig, 8))
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return 1; /* bad signature */
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/* could pass pointers to user-defined error handlers instead of NULLs: */
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png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
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if (!png_ptr)
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return 4; /* out of memory */
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info_ptr = png_create_info_struct(png_ptr);
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if (!info_ptr) {
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png_destroy_read_struct(&png_ptr, NULL, NULL);
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return 4; /* out of memory */
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}
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/* we could create a second info struct here (end_info), but it's only
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* useful if we want to keep pre- and post-IDAT chunk info separated
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* (mainly for PNG-aware image editors and converters) */
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/* setjmp() must be called in every function that calls a PNG-reading
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* libpng function */
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if (setjmp(png_jmpbuf(png_ptr))) {
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png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
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return 2;
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}
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png_init_io(png_ptr, infile);
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png_set_sig_bytes(png_ptr, 8); /* we already read the 8 signature bytes */
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png_read_info(png_ptr, info_ptr); /* read all PNG info up to image data */
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/* alternatively, could make separate calls to png_get_image_width(),
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* etc., but want bit_depth and color_type for later [don't care about
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* compression_type and filter_type => NULLs] */
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png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type,
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NULL, NULL, NULL);
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*pWidth = width;
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*pHeight = height;
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/* OK, that's all we need for now; return happy */
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return 0;
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}
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/* returns 0 if succeeds, 1 if fails due to no bKGD chunk, 2 if libpng error;
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* scales values to 8-bit if necessary */
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int readpng_get_bgcolor(uch *red, uch *green, uch *blue)
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{
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png_color_16p pBackground;
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/* setjmp() must be called in every function that calls a PNG-reading
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* libpng function */
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if (setjmp(png_jmpbuf(png_ptr))) {
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png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
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return 2;
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}
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if (!png_get_valid(png_ptr, info_ptr, PNG_INFO_bKGD))
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return 1;
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/* it is not obvious from the libpng documentation, but this function
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* takes a pointer to a pointer, and it always returns valid red, green
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* and blue values, regardless of color_type: */
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png_get_bKGD(png_ptr, info_ptr, &pBackground);
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/* however, it always returns the raw bKGD data, regardless of any
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* bit-depth transformations, so check depth and adjust if necessary */
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if (bit_depth == 16) {
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*red = pBackground->red >> 8;
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*green = pBackground->green >> 8;
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*blue = pBackground->blue >> 8;
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} else if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8) {
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if (bit_depth == 1)
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*red = *green = *blue = pBackground->gray? 255 : 0;
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else if (bit_depth == 2)
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*red = *green = *blue = (255/3) * pBackground->gray;
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else /* bit_depth == 4 */
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*red = *green = *blue = (255/15) * pBackground->gray;
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} else {
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*red = (uch)pBackground->red;
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*green = (uch)pBackground->green;
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*blue = (uch)pBackground->blue;
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}
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return 0;
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}
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/* display_exponent == LUT_exponent * CRT_exponent */
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uch *readpng_get_image(double display_exponent, int *pChannels, ulg *pRowbytes)
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{
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double gamma;
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png_uint_32 i, rowbytes;
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png_bytepp row_pointers = NULL;
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/* setjmp() must be called in every function that calls a PNG-reading
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* libpng function */
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if (setjmp(png_jmpbuf(png_ptr))) {
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png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
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return NULL;
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}
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/* expand palette images to RGB, low-bit-depth grayscale images to 8 bits,
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* transparency chunks to full alpha channel; strip 16-bit-per-sample
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* images to 8 bits per sample; and convert grayscale to RGB[A] */
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if (color_type == PNG_COLOR_TYPE_PALETTE)
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png_set_expand(png_ptr);
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if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)
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png_set_expand(png_ptr);
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if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))
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png_set_expand(png_ptr);
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if (bit_depth == 16)
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png_set_strip_16(png_ptr);
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if (color_type == PNG_COLOR_TYPE_GRAY ||
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color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
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png_set_gray_to_rgb(png_ptr);
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/* unlike the example in the libpng documentation, we have *no* idea where
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* this file may have come from--so if it doesn't have a file gamma, don't
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* do any correction ("do no harm") */
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if (png_get_gAMA(png_ptr, info_ptr, &gamma))
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png_set_gamma(png_ptr, display_exponent, gamma);
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/* all transformations have been registered; now update info_ptr data,
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* get rowbytes and channels, and allocate image memory */
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png_read_update_info(png_ptr, info_ptr);
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*pRowbytes = rowbytes = png_get_rowbytes(png_ptr, info_ptr);
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*pChannels = (int)png_get_channels(png_ptr, info_ptr);
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if ((image_data = (uch *)malloc(rowbytes*height)) == NULL) {
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png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
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return NULL;
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}
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if ((row_pointers = (png_bytepp)malloc(height*sizeof(png_bytep))) == NULL) {
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png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
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free(image_data);
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image_data = NULL;
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return NULL;
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}
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Trace((stderr, "readpng_get_image: channels = %d, rowbytes = %ld, height = %ld\n", *pChannels, rowbytes, height));
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/* set the individual row_pointers to point at the correct offsets */
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for (i = 0; i < height; ++i)
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row_pointers[i] = image_data + i*rowbytes;
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/* now we can go ahead and just read the whole image */
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png_read_image(png_ptr, row_pointers);
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/* and we're done! (png_read_end() can be omitted if no processing of
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* post-IDAT text/time/etc. is desired) */
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free(row_pointers);
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row_pointers = NULL;
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png_read_end(png_ptr, NULL);
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return image_data;
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}
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void readpng_cleanup(int free_image_data)
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{
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if (free_image_data && image_data) {
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free(image_data);
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image_data = NULL;
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}
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if (png_ptr && info_ptr) {
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png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
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png_ptr = NULL;
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info_ptr = NULL;
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}
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}
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