brightness.c (like xbacklight, except it actually works for me)

brightness.c

/* brightness.c - Because xbacklight doesn't work for me.
 * Features: Cubic ease-in-out interpolation of brightness over time.
 *
 * Currently works with a single target device from /sys/class/backlight.
 * Previously only worked on intel_backlight, has since been adapted to search
 * for the proper controller.
 *
 * Ethan McTague <ethan@tague.me> - January 28, 2018
 * Public domain - free to use/modify without any restrictions.
 *
 * gcc brightness.c -o brightness -lm
 * sudo install -m a=rxs brightness /usr/local/bin
 */
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <unistd.h>
#include <dirent.h>

#define TARGET_DIR "/sys/class/backlight/"
#define BUF_SIZE 500


// Cubic bezier (ctrl points c1, c2 + anchor points a1, a2 + time u).
float
cubic_bezier (float u, float c1, float c2, float a1, float a2)
{
  return pow(u, 3) * (a2 + 3 * (c1 - c2) - a1) + 3 * pow(u, 2)
             * (a1 - 2 * c1 + c2) + 3 * u * (c1 - a1) + a1;
}


// Ease-in-out bezier (range: 0 to 1).
float
ease_in_out (float u)
{
  return cubic_bezier(u, .42, .58, 0, 1);
}


// Interpolate linearly between two values.
float
interpolate (float u, float a, float b) {
  return a + u * (b - a);
}


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

  // Complain if no value provided.
  if (argc != 2)
  {
    fprintf(stderr,
        "Usage: %s [+/-][value]\n\n"
        "Ethan McTague <ethan@tague.me> - January 28, 2018\n"
        "Public domain - free to use/modify without any restrictions.\n",
        argv[0]);
    return 1;
  }


  // Read the backlights directory to find the appropriate backlight controller.
  DIR* dir = opendir(TARGET_DIR);

  if (dir == NULL)
  {
    fprintf(stderr, "Could not open %s for file listing.\n", TARGET_DIR);
    return 2;
  }

  // Skip over '.' and '..'.
  readdir(dir); readdir(dir);

  // Complain if there aren't any backlights to control.
  struct dirent *ent = readdir(dir);
  if (ent == NULL || (ent->d_type != DT_DIR && ent->d_type != DT_LNK))
  {
    fprintf(stderr, "No subdirectories in %s.\n", TARGET_DIR);
    return 3;
  }

  // Write the target paths.
  char target_out[BUF_SIZE];
  char target_max[BUF_SIZE];
  snprintf(target_out, BUF_SIZE, TARGET_DIR "%s/brightness", ent->d_name);
  snprintf(target_max, BUF_SIZE, TARGET_DIR "%s/max_brightness", ent->d_name);

  closedir(dir);


  // Get value from first argument.
  int newval = atoi(argv[1]);


  // Get original value for smooth and relative.
  int orig;
  FILE* cur = fopen(target_out, "r");

  if (cur == NULL)
  {
    fprintf(stderr, "Could not open %s for reading.\n", target_out);
    return 2;
  }

  fscanf(cur, "%d", &orig);
  fclose(cur);
  

  // Relative positioning if '+' or '-' prefix is used.
  if (argv[1][0] == '+' || argv[1][0] == '-')
    newval = orig + newval;


  // Read maximum brightness.
  int max;
  FILE* maxin = fopen(target_max, "r");

  if (maxin == NULL)
  {
    fprintf(stderr, "Could not open %s for reading.\n", target_max);
    return 3;
  }

  fscanf(maxin, "%d", &max);
  fclose(maxin);


  // Clamp within valid range (and avoid 0 despite it being valid.)
  if (newval < 1) newval = 1;
  if (newval > max) newval = max;


  // Repeatedly quickly adjust brightness over time for a nice smooth change.
  for (float n = 0; n < 1; n += 0.01)
  {
    usleep(5000);

    // Save to output file.
    FILE* out = fopen(target_out, "w");
    if (out == NULL)
    {
      fprintf(stderr, "Could not open %s for writing.\n", target_out);
      return 4;
    }

    float ival = interpolate(ease_in_out(n), (float)orig, (float)newval);
    fprintf(out, "%d", (int)ival);
    fclose(out);
  }


  return 0;
}

build-install.sh

#!/bin/sh
gcc brightness.c -o brightness -lm
sudo install -m a=rxs brightness /usr/local/bin