ppm2png.c

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "lodepng.h"

#define IS_BLANK(ch) ((ch) == '\n' || (ch) == '\t' || (ch) == '\r' || (ch) == ' ' || (ch) == 0x7F)

static void ppmSkipLine(char **cur) {
    for (;;) {
        char ch = **cur;
        (*cur)++;
        
        if (ch == 0) {
            (*cur)--;
            break;
            
        } else if (ch == '\n') {
            break;
        }
    }
}

// read a number
static int ppmReadNumber(char **cur, unsigned int *res) {
    unsigned int value = 0;
    
    for (;;) {
        //int ch = fgetc(fp);
        char ch = **cur;
        (*cur)++;
        
        if (IS_BLANK(ch)) {
            // skip blank characters
            continue;
            
        } else if (ch == '#') {
            // skip the comment
            ppmSkipLine(cur);
            continue;
            
        } else if (ch >= '0' && ch <= '9') {
            // found a number, 
            value = ch - '0';
            break;
            
        } else if (ch == 0) {
            // EOF
            (*cur)--;
            
        } else {
            // found another character, it's invalid or EOF
            return 0;
        }
    }
    
    // read the number
    for (;;) {
        //int ch = fgetc(fp);
        char ch = **cur;
        (*cur)++;
        
        if (ch >= '0' && ch <= '9') {
            value = (value * 10) + (ch - '0');
            
        } else if (IS_BLANK(ch)) {
            break; // success
            
        } else if (ch == 0 || ch == '#') {
            (*cur)--;
            break; // success
            
        } else {
            // any other character is invalid or EOF
            return 0;
        }
    }
    
    *res = value;
    return 1;
}

#define READ_NUMBER(name) do { if (!ppmReadNumber(&cur, &(name))) { fprintf(stderr, "Failed to read " #name "\n"); return 1; } } while (0)

int main(int argc, char *argv[]) {
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <filename>\n", argv[0]);
        return 1;
    }
    
    FILE *fp = fopen(argv[1], "rb");
    if (!fp) {
        fprintf(stderr, "Failed to open %s\n", argv[1]);
        return 1;
    }
    
    // trying to buf everything
    fseek(fp, 0, SEEK_END);
    unsigned long size = ftell(fp);
    fseek(fp, 0, SEEK_SET);
    
    char *data = (char*)malloc(size+1);
    
    fread(data, 1, size, fp);
    data[size] = 0; // EOF
    
    char *cur = data;
    
    //fread(buf, 1, 2, fp);
    if (cur[0] != 'P' && cur[1] != '3') {
        fprintf(stderr, "File is not a PPM file\n");
        return 1;
    }
    
    cur += 2;
    
    unsigned int width, height;
    READ_NUMBER(width);
    READ_NUMBER(height);
    
    unsigned int maxval;
    READ_NUMBER(maxval);
    
    printf("Dimensions: %ux%u\n", width, height);
    
    unsigned char *image = (unsigned char*)malloc(width * height * 3);
    
    unsigned char *curimg = image;
    
    for (unsigned int x = 0; x < width; x++) {
        for (unsigned int y = 0; y < height; y++) {
            unsigned int red, green, blue;
            READ_NUMBER(red);
            READ_NUMBER(green);
            READ_NUMBER(blue);
            
            // do the division thingy
            red = (unsigned int)round(((double)red / (double)maxval) * 255.0);
            green = (unsigned int)round(((double)green / (double)maxval) * 255.0);
            blue = (unsigned int)round(((double)blue / (double)maxval) * 255.0);
            
            *curimg++ = red;
            *curimg++ = green;
            *curimg++ = blue;
        }
    }
    
    printf("Encoding PNG...\n");
    
    int length = strlen(argv[1]);
    char *target = (char*)malloc(length + 5);
    memcpy(target, argv[1], length+1);
    
    // get filename for target
    // if filename ends with ".ppm", replace with ".png"
    if (strcmp(target + length - 4, ".ppm") == 0) {
        memcpy(target + length - 4, ".png", 4);
        
    } else {
        // otherwise, just append png
        memcpy(target + length, ".png", 5); // include null terminator
    }
    
    unsigned error = lodepng_encode24_file(target, image, width, height);
    
    /*if there's an error, display it*/
    if(error) printf("error %u: %s\n", error, lodepng_error_text(error));
    return 0;
}