// compile ...
// gcc -std=gnu99 -Wall image.c -o image `pkg-config --cflags --libs gtk+-3.0`
// on thales@mathematik.uni-ulm.de

#include <gdk-pixbuf/gdk-pixbuf.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdbool.h>
#include <errno.h>


bool string_to_int(char* s, int* val) {
   char* endptr;
   errno = 0; /* reset errno */
   int i = strtol(s, &endptr, 10);
   if (endptr == s) return false; /* conversion failed */
   if (*endptr) return false; /* unexpected characters behind the integer */
   if (errno) return false; /* out of range */
   *val = i;
   return true;
}

bool string_to_double(char* s, double* val) {
   char* endptr;
   errno = 0; /* reset errno */
   double x = strtod(s, &endptr);
   if (endptr == s) return false; /* conversion failed */
   if (*endptr) return false; /* unexpected characters behind the double */
   if (errno) return false; /* out of range */
   *val = x;
   return true;
}

int main(int argc, char** argv) {
    g_type_init();
    
    // parameters
    int width = 100;
    int height = 100;
    
    // read command line arguments
    // ...
    
    // check arguments
    // ...
    
    // create image buffer:
    GdkPixbuf* pixbuf = gdk_pixbuf_new(GDK_COLORSPACE_RGB, FALSE, 8, width, height);
    // more info:  http://developer.gnome.org/gdk-pixbuf/stable/gdk-pixbuf-The-GdkPixbuf-Structure.html    

    int n_channels = gdk_pixbuf_get_n_channels (pixbuf); // == 3 because is_alpha(pixbuf) == FALSE
    // rowstride: number of bytes between the start of a row and the start of the next row
    //   --> also einfach Laenge einer Zeile; das habe ich in der Uebung falsch erklaert: Entschuldigung!
    int rowstride = gdk_pixbuf_get_rowstride (pixbuf); 
    guchar* pixels = gdk_pixbuf_get_pixels (pixbuf);
    
    for (int y = 0; y < height; ++y) {
        for (int x = 0; x < width; ++x) {
            // get pixel p
            guchar* p = pixels + y * rowstride + x * n_channels;
            // set RGB
            p[0] = 0; // red
            p[1] = 255; // green
            p[2] = 0; // blue
        }
    }
    
    // save image
    gdk_pixbuf_save (pixbuf, "image.jpg", "jpeg", NULL, "quality", "100", NULL);
}