write_png.c

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/*!
   \file lib/pngdriver/write_png.c
 
   \brief GRASS png display driver - write PPM image (lower level functions)
 
   (C) 2007-2014 by Glynn Clements and the GRASS Development Team
 
   This program is free software under the GNU General Public License
   (>=v2). Read the file COPYING that comes with GRASS for details.
 
   \author Glynn Clements
 */
 
#include <stdio.h>
#include <stdlib.h>
#include <png.h>
 
#include <grass/gis.h>
#include <grass/glocale.h>
 
#include "pngdriver.h"
 
static void write_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
    png_size_t check;
    FILE *fp;
 
    if (png_ptr == NULL)
        return;
 
    fp = (FILE *)png_get_io_ptr(png_ptr);
    if (fp == NULL)
        return;
 
    check = fwrite(data, 1, length, fp);
 
    if (check != length)
        G_fatal_error(_("Unable to write PNG"));
}
 
static void output_flush(png_structp png_ptr)
{
    FILE *fp;
 
    if (png_ptr == NULL)
        return;
 
    fp = (FILE *)png_get_io_ptr(png_ptr);
    if (fp == NULL)
        return;
 
    fflush(fp);
}
 
void write_png(void)
{
    static jmp_buf jbuf;
    static png_struct *png_ptr;
    static png_info *info_ptr;
    FILE *output;
    int x, y;
    unsigned int *p;
    png_bytep line;
    const char *str;
    int compress;
 
    png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, &jbuf, NULL, NULL);
    if (!png_ptr)
        G_fatal_error(_("Unable to allocate PNG structure"));
 
    info_ptr = png_create_info_struct(png_ptr);
    if (!info_ptr)
        G_fatal_error(_("Unable to allocate PNG structure"));
 
    if (setjmp(png_jmpbuf(png_ptr)))
        G_fatal_error(_("Unable to write PNG file"));
 
    output = fopen(png.file_name, "wb");
    if (!output)
        G_fatal_error(_("Unable to open output PNG file <%s>"), png.file_name);
 
    png_set_write_fn(png_ptr, output, write_data, output_flush);
 
    png_set_IHDR(png_ptr, info_ptr, png.width, png.height, 8,
                 png.true_color ? PNG_COLOR_TYPE_RGB_ALPHA
                                : PNG_COLOR_TYPE_PALETTE,
                 PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT,
                 PNG_FILTER_TYPE_DEFAULT);
 
    if (png.true_color)
        png_set_invert_alpha(png_ptr);
    else {
        png_color png_pal[256];
        int i;
 
        for (i = 0; i < 256; i++) {
            png_pal[i].red = png.palette[i][0];
            png_pal[i].green = png.palette[i][1];
            png_pal[i].blue = png.palette[i][2];
        }
 
        png_set_PLTE(png_ptr, info_ptr, png_pal, 256);
 
        if (png.has_alpha) {
            png_byte trans = (png_byte)0;
 
            png_set_tRNS(png_ptr, info_ptr, &trans, 1, NULL);
        }
    }
 
    str = getenv("GRASS_RENDER_FILE_COMPRESSION");
    if (str && sscanf(str, "%d", &compress) == 1)
        png_set_compression_level(png_ptr, compress);
 
    png_write_info(png_ptr, info_ptr);
 
    line = G_malloc(png.width * 4);
 
    for (y = 0, p = png.grid; y < png.height; y++) {
        png_bytep q = line;
 
        if (png.true_color)
            for (x = 0; x < png.width; x++, p++) {
                unsigned int c = *p;
                int r, g, b, a;
 
                png_get_pixel(c, &r, &g, &b, &a);
                *q++ = (png_byte)r;
                *q++ = (png_byte)g;
                *q++ = (png_byte)b;
                *q++ = (png_byte)a;
            }
        else
            for (x = 0; x < png.width; x++, p++, q++)
                *q = (png_byte)*p;
 
        png_write_row(png_ptr, line);
    }
 
    G_free(line);
 
    png_write_end(png_ptr, info_ptr);
 
    png_destroy_write_struct(&png_ptr, &info_ptr);
 
    fclose(output);
}