skb

/**************************************************************************************************
*
*       HOW TO REGULATE SCREEN BRIGHTNESS USING THE KEYBOARD IN AN OVERLY COMPLICATED WAY
*                                  You can compile this thing!!!
*
* This following tutorial is a command line utility in disguise.  It changes screen brightness  and
* other similar parameters,  i.e. those which are regulated by a text file which consists of *only*
* one integer. For instance, on my laptop, the screen brightness is regulated by the file
*
*            /sys/class/backlight/apple_backlight/brightness
*
* which is a simple text file containing the current screen brightness value.
* A similar parameter is keyboard brightness, which, on my laptop, is regulated by the file
*
*            /sys/class/leds/smc::kbd_backlight/brightness
*
* Obviously enough, by modifying those values I can modify screen and keyboard brightness.
* This utility does just that:  it reads the current value in those kind of files and changes it by
* the amount specified by the user.
* Yes, you can do this is one thousand different and probably better ways.  You can do this using a
* bash script, you can use xbacklight, whatever. Here is another, more intricate way.
*
* So, let's say you want to use this program to modify your screen brightness.
* First,  modify the path to the text file which regulates your screen brightness.  You can do this
* by changing the SCREEN_PATH definition below.  The first part of the path, /sys/class/backlight ,
* is likely to be the same for you too.
* Often  the screen brightness value must fall into a certain range.  You can define this range  by
* changing the MIN_SCREEN_BRIGHTNESS and MAX_SCREEN_BRIGHTNESS definitions below.
* Finally, compile the program by running:
*
*            # gcc skb.c -o skb
*
* You can now adjust your screen brightness by running:
*
*            # sudo ./skb -s n
*
* where n is the amount (positive or negative) by which you wish to modify the brightness.
*
* NOTE: since the file which regulates screen brightness is often write-protected, you are probably
*       required to run this program as root, i.e. using sudo.
*
*
* If  you also want to use this program to modify your keyboard brightness,  uncomment the keyboard
* definitions and the keyboard entry in the "case" construct, edit the path and the range and
* compile the program. You can now adjust your keyboard brightness by running:
*
*            # sudo ./skb -k n
*
* where n is the amount (positive or negative) by which you wish to modify the brightness.
*
* If  you want this program to modify parameter X which is regulated by a text file which  consists
* of  *only*  one integer, which integer must fall into a certain range, you can modify the generic
* deifinitions and the generic entry in the "case" construct to suit your needs.
*
*
* You can now move the compiled program skb to /usr/bin so that it can be found by your shell:
*
*            # sudo mv ./skb /usr/bin/
*
* For convenience,  you can allow your regular user to execute this program by adding the following
* line to your sudoers file (edit using the "visudo" command):
*
*            username ALL=NOPASSWD: /usr/bin/skb
*
* Lastly, and here comes the whole purpose of this thing, you can bind a keypress to its execution.
* This  way,  when  you  press that key your screen brightness will  change!  Isn't  that  magical?
* ... anyways, you can do this is many many ways.  If you use i3wm (and if you don't you're missing
* out) you can add the following line(s) to your config file:
*
*            bindsym a_key  exec sudo skb -s +1
*            bindsym another_key exec sudo skb -s -1
*            ...
*
* DONE
*
* FINAL NOTE: use this program at your own risk. It works well enough for me. I am just learning to
*             write in C.  If you find in this code some serious flaw that will cause a computer to
*             explode or worse,  please  report it to me.  You  can find me in the archlinux forums
*             under the name of stdi. If you just want to yell at me because this is most unuseful,
*             or because my english is so bad, again, archlinux forums.
*
**************************************************************************************************/

#include<stdio.h>
#include<stdlib.h>
#define ARG_NUM 3


/* Screen brightness configuration */
#define SCREEN_PATH "/sys/class/backlight/apple_backlight/brightness"
#define MIN_SCREEN_BRIGHTNESS 0
#define MAX_SCREEN_BRIGHTNESS 15


/* Keyboard brightness configuration */
/*
#define KEYBOARD_PATH "/sys/class/leds/smc::kbd_backlight/brightness"
#define MIN_KEYBOARD_BRIGHTNESS 0
#define MAX_KEYBOARD_BRIGHTNESS 255
*/


/* Generic parameter configuration */
/*
#define GENERIC_PATH "/path/to/a/file"
#define MIN_VALUE 0
#define MAX_VALUE 100
*/


/* Functions prototypes definition */
void change_file(char *file_path, int min, int max, int delta);

/*************************************************************************************************/

int main(int argc, char **argv){

   /* Definitions of required variables */
   int delta;

   /* Checks if the user called the program correctly */
   if(argc!=ARG_NUM){
      printf("\nRead the source code\n\n");
      return 0;
   }

   /* "Parses" the user input */
   sscanf(argv[2],"%d", &delta);

   /* Checks the user choice and execute the subsequent action */
   switch(argv[1][1]){


      /* To change screen brightness */
      case 's':
         change_file(SCREEN_PATH, MIN_SCREEN_BRIGHTNESS, MAX_SCREEN_BRIGHTNESS, delta);
         break;


      /* To change keyboard brightness */
      /*
      case 'k':
         change_file(KEYBOARD_PATH, MIN_KEYBOARD_BRIGHTNESS, MAX_KEYBOARD_BRIGHTNESS, delta);
         break;
      */


      /* To change parameter X */
      /*
      case 'g':
         change_file(GENERIC_PATH, MIN_VALUE, MAX_VALUE, delta)
         break;
      */


      default:
         printf("\nRead the source code\n\n");
         break;
   }

   return 0;

}


/*************************************************************************************************/


/*
*
* This function was written to edit those configuration files which consists of *only* one integer.
* One of those files is, for instance, the one that regulates the screen brightness.
* The function takes as input the path to the file (as a string of characters), the range where the
* integer in the file must fall (as max and min), and the amount by which changing the current
* value.
*
* WARNING: the content of the file is completely erased and replaced with the new value!
*
*/


void change_file(char *file_path, int min, int max, int delta){

   FILE *file_pointer;
   int init_value, final_value;

   /* Opens the file and checks it opened correctly */
   file_pointer=fopen(file_path, "r+");
   if(file_pointer==NULL){
      printf("Unable to open the file.\n");
      exit(1);
   }

   /* Reads the content of the file */
   fscanf(file_pointer, "%d", &init_value);

   /* Assigns the final value and makes sure it stays in the required range */
   final_value = init_value + delta;
   if(final_value>max)
      final_value=max;
   if(final_value<min)
      final_value=min;

   /* Goes to the beginning of the file and prints the final_value */
   rewind(file_pointer);
   fprintf(file_pointer, "%d", final_value);
   fclose(file_pointer);

}