feat(backlight): add brightness control

include/modules/backlight.hpp

@@ -50,6 +50,8 @@ class Backlight : public ALabel {
   template <class ForwardIt, class Inserter>
   static void enumerate_devices(ForwardIt first, ForwardIt last, Inserter inserter, udev *udev);
 
+  bool handleScroll(GdkEventScroll* e);
+
   const std::string preferred_device_;
   static constexpr int EPOLL_MAX_EVENTS = 16;
 

man/waybar-backlight.5.scd

@@ -58,16 +58,25 @@ The *backlight* module displays the current backlight level.
 
 *on-scroll-up*: ++
 	typeof: string ++
-	Command to execute when performing a scroll up on the module.
+	Command to execute when performing a scroll up on the module. This replaces the default behaviour of brightness control.
 
 *on-scroll-down*: ++
 	typeof: string
-	Command to execute when performing a scroll down on the module.
+	Command to execute when performing a scroll down on the module. This replaces the default behaviour of brightness control.
 
 *smooth-scrolling-threshold*: ++
 	typeof: double
 	Threshold to be used when scrolling.
 
+*reverse-scrolling*: ++
+	typeof: bool ++
+	Option to reverse the scroll direction.
+
+*scroll-step*: ++
+	typeof: float ++
+	default: 1.0 ++
+	The speed in which to change the brightness when scrolling.
+
 # EXAMPLE:
 
 ```

src/modules/backlight.cpp

@@ -106,6 +106,10 @@ waybar::modules::Backlight::Backlight(const std::string &id, const Json::Value &
     dp.emit();
   }
 
+  // Set up scroll handler
+  event_box_.add_events(Gdk::SCROLL_MASK | Gdk::SMOOTH_SCROLL_MASK);
+  event_box_.signal_scroll_event().connect(sigc::mem_fun(*this, &Backlight::handleScroll));
+
   udev_thread_ = [this] {
     std::unique_ptr<udev, UdevDeleter> udev{udev_new()};
     check_nn(udev.get(), "Udev new failed");
@@ -264,3 +268,71 @@ void waybar::modules::Backlight::enumerate_devices(ForwardIt first, ForwardIt la
     upsert_device(first, last, inserter, dev.get());
   }
 }
+
+bool waybar::modules::Backlight::handleScroll(GdkEventScroll *e) {
+  // Check if the user has set a custom command for scrolling
+  if (config_["on-scroll-up"].isString() || config_["on-scroll-down"].isString()) {
+    return AModule::handleScroll(e);
+  }
+
+  // Check scroll direction
+  auto dir = AModule::getScrollDir(e);
+  if (dir == SCROLL_DIR::NONE) {
+    return true;
+  }
+
+  if (config_["reverse-scrolling"].asBool()) {
+    if (dir == SCROLL_DIR::UP) {
+      dir = SCROLL_DIR::DOWN;
+    } else if (dir == SCROLL_DIR::DOWN) {
+      dir = SCROLL_DIR::UP;
+    }
+  }
+
+  // Get scroll step
+  double step = 1;
+
+  if (config_["scroll-step"].isDouble()) {
+    step = config_["scroll-step"].asDouble();
+  }
+
+  // Get the best device
+  decltype(devices_) devices;
+  {
+    std::scoped_lock<std::mutex> lock(udev_thread_mutex_);
+    devices = devices_;
+  }
+  const auto best = best_device(devices.cbegin(), devices.cend(), preferred_device_);
+
+  if (best == nullptr) {
+    return true;
+  }
+
+  // Compute the absolute step
+  const auto abs_step = static_cast<int>(round(step * best->get_max() / 100.0f));
+
+  // Compute the new value
+  int new_value = best->get_actual();
+
+  if (dir == SCROLL_DIR::UP) {
+      new_value += abs_step;
+  } else if (dir == SCROLL_DIR::DOWN) {
+      new_value -= abs_step;
+  }
+
+  // Clamp the value
+  new_value = std::clamp(new_value, 0, best->get_max());
+
+  // Get a udev instance
+  std::unique_ptr<udev, UdevDeleter> udev{udev_new()};
+  check_nn(udev.get(), "Udev new failed");
+
+  // Get the udev device
+  std::unique_ptr<udev_device, UdevDeviceDeleter> dev{udev_device_new_from_subsystem_sysname(udev.get(), "backlight", std::string(best->name()).c_str())};
+  check_nn(dev.get(), "Udev device new failed");
+
+  // Set the new value
+  udev_device_set_sysattr_value(dev.get(), "brightness", std::to_string(new_value).c_str());
+
+  return true;
+}