ben-blinkenlights/ubb-vga/ppm.c

/*
 * ppm.c - Load a PPM image
 *
 * Written 2010-2011 by Werner Almesberger
 * Copyright 2010-2011 Werner Almesberger
 *
 * 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.
 */


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

#include "ppm.h"


static char *fgets_comment(char *line, int n, FILE *file)
{
	do {
		if (!fgets(line, n, file))
			return NULL;
	}
	while (*line == '#');
	return line;
}


uint8_t *load_ppm(const char *name, int *x, int *y)
{
	FILE *file;
	char line[100];
	int this_x, this_y, depth;
	int n;
	uint8_t *img;

	file = fopen(name, "r");
	if (!file) {
		perror(name);
		exit(1);
	}
	if (!fgets_comment(line, sizeof(line), file)) {
		fprintf(stderr, "can't read file type\n");
		exit(1);
	}
	if (strcmp(line, "P6\n")) {
		fprintf(stderr, "file type must be P6, not %s", line);
		exit(1);
	}
	if (!fgets_comment(line, sizeof(line), file)) {
		fprintf(stderr, "can't read resolution\n");
		exit(1);
	}
	if (sscanf(line, "%d %d", &this_x, &this_y) != 2) {
		fprintf(stderr, "can't parse resolution: %s", line);
		exit(1);
	}
	if (*x || *y) {
		if (*x != this_x || *y != this_y) {
			fprintf(stderr,
			    "resolution changed from %dx%d to %dx%d\n",
			    *x, *y, this_x, this_y);
			exit(1);
		}
	} else {
		*x = this_x;
		*y = this_y;
	}
	if (!fgets_comment(line, sizeof(line), file)) {
		fprintf(stderr, "can't read depth\n");
		exit(1);
	}
	if (sscanf(line, "%d", &depth) != 1) {
		fprintf(stderr, "can't parse depth: %s", line);
		exit(1);
	}
	if (depth != 255) {
		fprintf(stderr, "depth must be 255, not %d\n", depth);
		exit(1);
	}
	n = *x**y*3;
	img = malloc(n);
	if (!img) {
		perror("malloc");
		exit(1);
	}
	if (fread(img, 1, n, file) != n) {
		fprintf(stderr, "can't read %d bytes\n", n);
		exit(1);
	}
	fclose(file);
	return img;
}