PHOTOMETRY --- doom-emacs -- automatic theme adjustment based on ambient light

README.md

Adding automatic light/dark theme switching to doom-emacs running on a mac with ambient light sensor.

Idea adapted from: Matt Bilyeu https://matthewbilyeu.com/blog/2018-04-09/setting-emacs-theme-based-on-ambient-light

Installation

1. Make the lmutracker executable using clang and place it in your custom doom directory:

   $ cd ~/.doom.d/    # start in your custom doom directory, wherever that is for you.
   $ touch lmutracker.mm # copy in the contents of this file however you like
   $ clang -o lmutracker lmutracker.mm -framework IOKit -framework CoreFoundation  # this makes the executable
   

2. Add the relevant elisp to your doom config (e.g. "~/.doom.d/config.el") Edit values for light-theme and dark-theme to match your preferences.
3. Restart emacs and watch the theme automatically adjust to ambient light. By default, light sensor is probed every 10seconds. Use keybind SPC t p to toggle photometry on/off.

config.el

;; photometry
;; I want to be able to toggle "photometry" (automatic theme switching),
;; but I don't know how to properly build a module or properly code in elisp.

;; Here I start by defining an integer variable that tracks the state of
;; photometry being on or off.
(defvar photometry-mode 0)  ; photometry is recorded as "off"

;; Set light and dark theme choices here!
(defconst light-theme 'doom-solarized-light)
(defconst dark-theme 'doom-nova)

(defun photometry ()
  "Function for sensing light and changing themes based on apparent brightness
as reported through lmutracker executable."
  (let* ((current-light-sensor-reading
          (string-to-number
           (shell-command-to-string
            ;; this assumes you put the `lmutracker` executable
            ;; in your doom-config directory ("~/.doom.d/" or "~/.config/doom/")
            (concat doom-private-dir "lmutracker")))))
    (if (< current-light-sensor-reading 100000) ; test if environment is low-light
        (unless (eq doom-theme dark-theme) ; if theme is not yet dark
          (setq doom-theme dark-theme)     ; change to dark theme
          (doom//reload-theme))
      (when (eq doom-theme dark-theme)     ; if theme is dark
        (setq doom-theme light-theme)      ; change to light theme
        (doom//reload-theme)))))

(defun photometry/toggle ()
  "Toggle photometry on/off. Photometry is a function that changes the theme
over time based on ambient light sensor readings."
  (interactive)
  (if (zerop photometry-mode)
      (and (setq photometry-mode (1+ photometry-mode))
           (run-with-timer 0 10 #'photometry)) ; integer controls the update interval
    (and (setq photometry-mode (1- photometry-mode))
         (cancel-function-timers 'photometry))))

;; Add keybind so photometry can be toggled with `SPC t p`
(map! (:leader
        (:desc "toggle" :prefix "t"
          :desc "Photometry" :n "p" #'photometry/toggle)))

;; When on mac, use photometry for automatic theme adjustment
(when (eq system-type 'darwin)
  (setq doom-theme dark-theme) ; starting (dark) theme
  (photometry/toggle))         ; toggle photometry on!

lmutracker.mm

// lmutracker.mm
//
// clang -o lmutracker lmutracker.mm -framework IOKit -framework CoreFoundation
// 
// copied from Matt Bilyeu <https://matthewbilyeu.com/blog/2018-04-09/setting-emacs-theme-based-on-ambient-light>

#include <mach/mach.h>
#import <IOKit/IOKitLib.h>
#import <CoreFoundation/CoreFoundation.h>

static double updateInterval = 0.1;
static io_connect_t dataPort = 0;

void updateTimerCallBack(CFRunLoopTimerRef timer, void *info) {
  kern_return_t kr;
  uint32_t outputs = 2;
  uint64_t values[outputs];

  kr = IOConnectCallMethod(dataPort, 0, nil, 0, nil, 0, values, &outputs, nil, 0);
  if (kr == KERN_SUCCESS) {
    printf("%8lld", values[0]);
    exit(0);
  }

  if (kr == kIOReturnBusy) {
    return;
  }

  mach_error("I/O Kit error:", kr);
  exit(kr);
}

int main(void) {
  kern_return_t kr;
  io_service_t serviceObject;
  CFRunLoopTimerRef updateTimer;

  serviceObject = IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching("AppleLMUController"));
  if (!serviceObject) {
    fprintf(stderr, "failed to find ambient light sensors\n");
    exit(1);
  }

  kr = IOServiceOpen(serviceObject, mach_task_self(), 0, &dataPort);
  IOObjectRelease(serviceObject);
  if (kr != KERN_SUCCESS) {
    mach_error("IOServiceOpen:", kr);
    exit(kr);
  }

  setbuf(stdout, NULL);

  updateTimer = CFRunLoopTimerCreate(kCFAllocatorDefault,
                  CFAbsoluteTimeGetCurrent() + updateInterval, updateInterval,
                  0, 0, updateTimerCallBack, NULL);
  CFRunLoopAddTimer(CFRunLoopGetCurrent(), updateTimer, kCFRunLoopDefaultMode);
  CFRunLoopRun();

  exit(0);
}

it's doesn't works anymore on new Macbooks (with touchbar)

https://stackoverflow.com/a/52150583/1397675