I dunno that this makes it any easier...

I tried splitting up the sources to speed
up some compiling... but it didn't help.
I dunno that it's more readable this way.

I'm checkpointing this just in case.

backlight.cc

@@ -0,0 +1,65 @@
+#include "backlight.h"
+
+#include <iostream>
+#include <fstream>
+#include <algorithm>
+
+#include "power_console.h"
+
+int
+getBacklightPercent( const std::filesystem::path &backlightPath )
+{
+	std::ifstream i_max{ backlightPath / "max_brightness" };
+
+	int max;
+	i_max >> max;
+
+
+	std::ifstream inf{ backlightPath / "brightness" };
+	int in;
+	inf >> in;
+
+	return 100 * in / max;
+}
+
+std::filesystem::path getBacklightPath();
+
+
+namespace
+{
+	void
+	changeBrightness( int pct )
+	{
+		std::ifstream i_max{ getBacklightPath() / "max_brightness" };
+
+		int max;
+		i_max >> max;
+
+		// Clamp to never hit 0 backlight or pass max.
+		int adj= std::clamp( max * pct / 100, 1, max );
+		std::cerr << "Adjustment computed: " << adj << std::endl;
+
+		std::ofstream out{ getBacklightPath() / "brightness" };
+		out << adj;
+	}
+
+	void
+	increaseBrightness( int pct )
+	{
+		changeBrightness( pct );
+	}
+
+	void
+	decreaseBrightness( int pct )
+	{
+		changeBrightness( -pct );
+	}
+}
+
+void
+adjustBrightness( MouseWheelSlider *, void * )
+{
+	const int amount= brightness->value();
+	std::cerr << "Adjusting brightness by " << amount << std::endl;
+	changeBrightness( amount );
+}