diff options
Diffstat (limited to 'example.c')
| -rw-r--r-- | example.c | 54 |
1 files changed, 39 insertions, 15 deletions
@@ -2,18 +2,19 @@ #if 0 /* in case someone actually tries to compile this */ /* example.c - an example of using libpng - * Last changed in libpng 1.4.2 [May 6, 2010] - * This file has been placed in the public domain by the authors. - * Maintained 1998-2010 Glenn Randers-Pehrson - * Maintained 1996, 1997 Andreas Dilger) - * Written 1995, 1996 Guy Eric Schalnat, Group 42, Inc.) + * Last changed in libpng 1.5.7 [December 15, 2011] + * Maintained 1998-2011 Glenn Randers-Pehrson + * Maintained 1996, 1997 Andreas Dilger + * Written 1995, 1996 Guy Eric Schalnat, Group 42, Inc. */ /* This is an example of how to use libpng to read and write PNG files. - * The file libpng.txt is much more verbose then this. If you have not + * The file libpng-manual.txt is much more verbose then this. If you have not * read it, do so first. This was designed to be a starting point of an * implementation. This is not officially part of libpng, is hereby placed * in the public domain, and therefore does not require a copyright notice. + * To the extent possible under law, the authors have waived all copyright and + * related or neighboring rights to this file. * * This file does not currently compile, because it is missing certain * parts, like allocating memory to hold an image. You will have to @@ -22,6 +23,10 @@ * see also the programs in the contrib directory. */ +#define _POSIX_SOURCE 1 /* libpng and zlib are POSIX-compliant. You may + * change this if your application uses non-POSIX + * extensions. */ + #include "png.h" /* The png_jmpbuf() macro, used in error handling, became available in @@ -31,7 +36,7 @@ */ #ifndef png_jmpbuf -# define png_jmpbuf(png_ptr) ((png_ptr)->jmpbuf) +# define png_jmpbuf(png_ptr) ((png_ptr)->png_jmpbuf) #endif /* Check to see if a file is a PNG file using png_sig_cmp(). png_sig_cmp() @@ -183,8 +188,15 @@ void read_png(FILE *fp, unsigned int sig_read) /* File is already open */ * are mutually exclusive. */ - /* Tell libpng to strip 16 bit/color files down to 8 bits/color */ + /* Tell libpng to strip 16 bit/color files down to 8 bits/color. + * Use accurate scaling if it's available, otherwise just chop off the + * low byte. + */ +#ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED + png_set_scale_16(png_ptr); +#else png_set_strip_16(png_ptr); +#endif /* Strip alpha bytes from the input data without combining with the * background (not recommended). @@ -286,7 +298,6 @@ void read_png(FILE *fp, unsigned int sig_read) /* File is already open */ /* An array of colors to which the image should be quantized */ png_color std_color_cube[MAX_SCREEN_COLORS]; - /* Prior to libpng-1.4.2, this was png_set_dither(). */ png_set_quantize(png_ptr, std_color_cube, MAX_SCREEN_COLORS, MAX_SCREEN_COLORS, NULL, 0); } @@ -331,11 +342,16 @@ void read_png(FILE *fp, unsigned int sig_read) /* File is already open */ /* Add filler (or alpha) byte (before/after each RGB triplet) */ png_set_filler(png_ptr, 0xff, PNG_FILLER_AFTER); +#ifdef PNG_READ_INTERLACING_SUPPORTED /* Turn on interlace handling. REQUIRED if you are not using * png_read_image(). To see how to handle interlacing passes, * see the png_read_row() method below: */ number_passes = png_set_interlace_handling(png_ptr); +#else + number_passes = 1; +#endif /* PNG_READ_INTERLACING_SUPPORTED */ + /* Optional call to gamma correct and add the background to the palette * and update info structure. REQUIRED if you are expecting libpng to @@ -517,6 +533,7 @@ row_callback(png_structp png_ptr, png_bytep new_row, */ png_bytep old_row = ((png_bytep *)our_data)[row_num]; +#ifdef PNG_READ_INTERLACING_SUPPORTED /* If both rows are allocated then copy the new row * data to the corresponding row data. */ @@ -545,6 +562,7 @@ row_callback(png_structp png_ptr, png_bytep new_row, * to pass the current row as new_row, and the function will combine * the old row and the new row. */ +#endif /* PNG_READ_INTERLACING_SUPPORTED */ } end_callback(png_structp png_ptr, png_infop info) @@ -656,14 +674,18 @@ void write_png(char *file_name /* , ... other image information ... */) /* Optional significant bit (sBIT) chunk */ png_color_8 sig_bit; + /* If we are dealing with a grayscale image then */ sig_bit.gray = true_bit_depth; + /* Otherwise, if we are dealing with a color image then */ sig_bit.red = true_red_bit_depth; sig_bit.green = true_green_bit_depth; sig_bit.blue = true_blue_bit_depth; + /* If the image has an alpha channel then */ sig_bit.alpha = true_alpha_bit_depth; + png_set_sBIT(png_ptr, info_ptr, &sig_bit); @@ -676,20 +698,21 @@ void write_png(char *file_name /* , ... other image information ... */) text_ptr[0].key = "Title"; text_ptr[0].text = "Mona Lisa"; text_ptr[0].compression = PNG_TEXT_COMPRESSION_NONE; + text_ptr[0].itxt_length = 0; + text_ptr[0].lang = NULL; + text_ptr[0].lang_key = NULL; text_ptr[1].key = "Author"; text_ptr[1].text = "Leonardo DaVinci"; text_ptr[1].compression = PNG_TEXT_COMPRESSION_NONE; + text_ptr[1].itxt_length = 0; + text_ptr[1].lang = NULL; + text_ptr[1].lang_key = NULL; text_ptr[2].key = "Description"; text_ptr[2].text = "<long text>"; text_ptr[2].compression = PNG_TEXT_COMPRESSION_zTXt; -#ifdef PNG_iTXt_SUPPORTED - text_ptr[0].lang = NULL; - text_ptr[0].lang_key = NULL; - text_ptr[1].lang = NULL; - text_ptr[1].lang_key = NULL; + text_ptr[2].itxt_length = 0; text_ptr[2].lang = NULL; text_ptr[2].lang_key = NULL; -#endif png_set_text(png_ptr, info_ptr, text_ptr, 3); /* Other optional chunks like cHRM, bKGD, tRNS, tIME, oFFs, pHYs */ @@ -754,6 +777,7 @@ void write_png(char *file_name /* , ... other image information ... */) /* Turn on interlace handling if you are not using png_write_image() */ if (interlacing) number_passes = png_set_interlace_handling(png_ptr); + else number_passes = 1; |