WIP PNG to RGB values

png-to-rgb.cpp

// based off the code from http://zarb.org/~gc/html/libpng.html but simplified/stripped down by Lockheedmartin.
// Conversion to C++ by wolfy1339
#include <unistd.h>
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <cstdarg>
#include <png.h>

int x, y, width, height, r, g, b;

png_byte color_type;
png_byte bit_depth;

png_structp png_ptr;
png_infop info_ptr;
int num_passes;
png_bytep* row_pointers;


void exit_error(const char *s,...) {
        va_list args;
        va_start(args, s);
        vfprintf(stderr, s, args);
        fprintf(stderr, "\n");
        va_end(args);
        abort();
}
/*void exit_error(const char *s) {
	printf(s);
	printf("\n");
	abort();
}*/
int main(int argc, char ** argv) {
	if (argc == 1) {
		exit_error("No filename given");
	}

	char header[8];
	FILE *fp = fopen(argv[1], "rb");
	if (!fp) {
		exit_error("[reading file] File %s cannot be opened.", argv[1]);
		//exit_error("[reading file] File cannot be opened.");
	}
	fread(header, 1, 8, fp);
	if (png_sig_cmp(header, 0, 8)) 
		exit_error("[reading file] File %s is not a PNG file.", argv[1]);
		//exit_error("[reading file] File is not a PNG file.");


	png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, nullptr, nullptr, nullptr);
	if (!png_ptr)
		exit_error("[reading file] png_create_read_struct failed.");
	info_ptr=png_create_info_struct(png_ptr);
	if (!info_ptr)
		exit_error("[reading file] png_create_info_struct failed.");
	if (setjmp(png_jmpbuf(png_ptr)))
		exit_error("[reading file] Error during init_io");

	png_init_io(png_ptr, fp);
	png_set_sig_bytes(png_ptr, 8);
	png_read_info(png_ptr, info_ptr);
	
	width  = png_get_image_width(png_ptr, info_ptr);
	height = png_get_image_height(png_ptr, info_ptr);
	color_type = png_get_color_type(png_ptr, info_ptr);
	bit_depth = png_get_bit_depth(png_ptr, info_ptr);

	num_passes = png_set_interlace_handling(png_ptr);
	png_read_update_info(png_ptr, info_ptr);

	if (setjmp(png_jmpbuf(png_ptr)))
		exit_error("[reading file] Error during read_image");

	row_pointers = (png_bytep*) malloc(sizeof(png_bytep) * height);
	for (y=0; y < height; y++)
		row_pointers[y] = (png_byte*) malloc(png_get_rowbytes(png_ptr, info_ptr));

	png_read_image(png_ptr, row_pointers);

	fclose(fp);

	if (!((color_type == PNG_COLOR_TYPE_RGB)||(color_type == PNG_COLOR_TYPE_RGBA))) 
		exit_error("[print color info] Image is not RGB or RGBA...");

	for (y=0; y < height; y++) {
		png_byte* row = row_pointers[y];
		for (x=0; x<width; x++) {
			if (color_type == PNG_COLOR_TYPE_RGB) {
				png_byte *ptr = &(row[x*3]);
				printf("Pixel at position (%d,%d) has RGBA values (%d,%d,%d,%d)", x ,y, ptr[0], ptr[1], ptr[2], 0);
			}
			if (color_type == PNG_COLOR_TYPE_RGBA) {
				png_byte *ptr = &(row[x*4]);
				printf("Pixel at position (%d,%d) has RGBA values (%d,%d,%d,%d)", x, y, ptr[0], ptr[1], ptr[2], ptr[3]);
			}
			printf("\n");
		}
	}
	return 0;
}