pngio.h from FreePop at Krugle

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// Helper functions for reading a writing PNG files.
// By Brendon Higgins: bh_doc@users.sf.net
// Released in Nov 2003 under GPL. See www.gnu.org if you don't know what that is.

#include <stdio.h>
#include <png.h>
    
typedef struct {
    unsigned char red, green, blue, alpha;
} colour;

typedef struct {
    FILE* fp;
    png_structp png;
    png_infop info;
    png_infop end;
    colour** rows;
} pngstuff;

int open_png(char *filename, pngstuff* ret) {
    png_uint_32 width, height;
    int y, bit_depth, colour_type, interlace_type;

    ret->fp = fopen(filename, "rb");
    if (!ret->fp) {
        return 1;
    }

    ret->png = png_create_read_struct(
        PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    if (!ret->png) {
        fclose(ret->fp);
        return 2;
    }

    ret->info = png_create_info_struct(ret->png);
    if (!ret->info) {
        png_destroy_read_struct(&ret->png, NULL, NULL);
        fclose(ret->fp);
        return 3;
    }

    ret->end = png_create_info_struct(ret->png);
    if (!ret->end) {
        png_destroy_read_struct(&ret->png, &ret->info, NULL);
        fclose(ret->fp);
        return 4;
    }

    if (setjmp(png_jmpbuf(ret->png))) {
        png_destroy_read_struct(&ret->png, &ret->info, &ret->end);
        fclose(ret->fp);
        return 5;
    }

    png_init_io(ret->png, ret->fp);
    png_read_info(ret->png, ret->info);
    png_get_IHDR(ret->png, ret->info, &width, &height, &bit_depth,
        &colour_type, &interlace_type, NULL, NULL);
    png_set_strip_16(ret->png);
    png_set_packing(ret->png);
    if (colour_type == PNG_COLOR_TYPE_PALETTE) {
        png_set_palette_to_rgb(ret->png);
    }

    if (colour_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8) {
        png_set_gray_1_2_4_to_8(ret->png);
    }
      
    if (png_get_valid(ret->png, ret->info, PNG_INFO_tRNS)) {
        png_set_tRNS_to_alpha(ret->png);
    }
        
    png_set_filler(ret->png, 0xff, PNG_FILLER_AFTER);
    
    if (colour_type == PNG_COLOR_TYPE_GRAY ||
        colour_type == PNG_COLOR_TYPE_GRAY_ALPHA) {
        png_set_gray_to_rgb(ret->png);
    }

    ret->rows = (colour**) malloc(height * sizeof(colour*));
    for (y = 0; y < height; ++y) {
        ret->rows[y] = (colour*) malloc(width * sizeof(colour));
    }

    png_read_image(ret->png, (png_bytepp) ret->rows);
    png_read_end(ret->png, ret->info);
    
    return 0;
}

void close_png(pngstuff* p) {
    png_destroy_read_struct(&p->png, &p->info, &p->end);
    fclose(p->fp);
    p->fp = NULL;
}

int write_png(char* filename, colour** rows, int width, int height) {
    FILE* fp_out;
    png_structp ppng_out;
    png_infop pinfo_out;

    fp_out = fopen(filename, "wb");
    if (!fp_out) {
        return 1;
    }
    
    ppng_out = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    if (!ppng_out) {
        fclose(fp_out);
        return 2;
    }
    
    pinfo_out = png_create_info_struct(ppng_out);
    if (!pinfo_out) {
        png_destroy_write_struct(&ppng_out, NULL);
        fclose(fp_out);
        return 3;
    }
        
    png_init_io(ppng_out, fp_out);
    png_set_IHDR(ppng_out, pinfo_out, width, height, 8,
        PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE,
        PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
    
    png_set_rows(ppng_out, pinfo_out, (png_bytepp)rows);

    if (setjmp(png_jmpbuf(ppng_out))) {
        png_destroy_write_struct(&ppng_out, &pinfo_out);
        fclose(fp_out);
        return 4;
    }

    png_write_png(ppng_out, pinfo_out, PNG_TRANSFORM_IDENTITY, NULL);

    png_destroy_write_struct(&ppng_out, &pinfo_out);
    fclose(fp_out);
    
    return 0;
}
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