slim/png.c

/****************************************************************************
    png.c - read and write png images using libpng routines.
    Distributed with Xplanet.
    Copyright (C) 2002 Hari Nair <hari@alumni.caltech.edu>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
****************************************************************************/

#include <stdio.h>
#include <stdlib.h>

#include <png.h>

int
read_png(const char *filename, int *width, int *height, unsigned char **rgb, 
	 unsigned char **alpha)
{
    FILE *infile = fopen(filename, "rb");

    png_structp png_ptr;
    png_infop info_ptr;
    png_bytepp row_pointers;

    unsigned char *ptr = NULL;
    png_uint_32 w, h;
    int bit_depth, color_type, interlace_type;
    int i;

    png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, 
                                     (png_voidp) NULL, 
                                     (png_error_ptr) NULL, 
                                     (png_error_ptr) NULL);
    if (!png_ptr) 
    {
        fclose(infile);
        return(0);
    }
  
    info_ptr = png_create_info_struct(png_ptr);
    if (!info_ptr)
    {
        png_destroy_read_struct(&png_ptr, (png_infopp) NULL, 
                                (png_infopp) NULL);
        fclose(infile);
        return(0);
    }
  
    if (setjmp(png_ptr->jmpbuf))
    {
        png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp) NULL);
        fclose(infile);
        return(0);
    }
  
    png_init_io(png_ptr, infile);
    png_read_info(png_ptr, info_ptr);

    png_get_IHDR(png_ptr, info_ptr, &w, &h, &bit_depth, &color_type,
                 &interlace_type, (int *) NULL, (int *) NULL);

    *width = (int) w;
    *height = (int) h;
    
    if (color_type == PNG_COLOR_TYPE_RGB_ALPHA
	|| color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
    {
	alpha[0] = malloc(*width * *height);
	if (alpha[0] == NULL)
	{
	    fprintf(stderr, "Can't allocate memory for alpha channel in PNG file.\n");
	    return(0); 
	}
    }

    /* Change a paletted/grayscale image to RGB */
    if (color_type == PNG_COLOR_TYPE_PALETTE && bit_depth <= 8) 
        png_set_expand(png_ptr);

    /* Change a grayscale image to RGB */
    if (color_type == PNG_COLOR_TYPE_GRAY 
        || color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
        png_set_gray_to_rgb(png_ptr);

    /* If the PNG file has 16 bits per channel, strip them down to 8 */
    if (bit_depth == 16) png_set_strip_16(png_ptr);

    /* use 1 byte per pixel */
    png_set_packing(png_ptr);

    row_pointers = malloc(*height * sizeof(png_bytep));
    if (row_pointers == NULL)
    {
        fprintf(stderr, "Can't allocate memory for PNG file.\n");
        return(0);
    }

    for (i = 0; i < *height; i++)
    {
        row_pointers[i] = malloc(4 * *width);
        if (row_pointers == NULL)
        {
            fprintf(stderr, "Can't allocate memory for PNG line.\n");
            return(0);
        }
    }

    png_read_image(png_ptr, row_pointers);

    rgb[0] = malloc(3 * *width * *height);
    if (rgb[0] == NULL)
    {
        fprintf(stderr, "Can't allocate memory for PNG file.\n");
        return(0);
    }

    if (alpha[0] == NULL)
    {
	ptr = rgb[0];
	for (i = 0; i < *height; i++)
	{
	    memcpy(ptr, row_pointers[i], 3 * *width);
	    ptr += 3 * *width;
	}
    }
    else
    {
	int j;
	ptr = rgb[0];
	for (i = 0; i < *height; i++)
	{
	    int ipos = 0;
	    for (j = 0; j < *width; j++)
	    {
		*ptr++ = row_pointers[i][ipos++];
		*ptr++ = row_pointers[i][ipos++];
		*ptr++ = row_pointers[i][ipos++];
		alpha[0][i * *width + j] = row_pointers[i][ipos++];
	    }
	}
    }

    png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp) NULL);

    for (i = 0; i < *height; i++) free(row_pointers[i]);
    free(row_pointers);

    fclose(infile);
    return(1);
}