Adjust the physical monitor brightness directly instead of multiplying gamma

LightBulb.PlatformInterop/DeviceContext.cs

@@ -1,11 +1,16 @@
-using System.Diagnostics;
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
 using System.Runtime.InteropServices;
 using LightBulb.PlatformInterop.Internal;
 
 namespace LightBulb.PlatformInterop;
 
-public partial class DeviceContext(nint handle) : NativeResource(handle)
+public partial class DeviceContext(nint handle, IReadOnlyList<PhysicalMonitor> physicalMonitors)
+    : NativeResource(handle)
 {
+    private readonly IReadOnlyList<PhysicalMonitor> _physicalMonitors = physicalMonitors;
     private int _gammaChannelOffset;
 
     private void SetGammaRamp(GammaRamp ramp)
@@ -48,10 +53,46 @@ public void SetGamma(double redMultiplier, double greenMultiplier, double blueMu
         SetGammaRamp(ramp);
     }
 
+    public void SetBrightness(double brightness)
+    {
+        // Brightness is a value from 0.0 to 1.0, convert to 0-100
+        var brightnessPercentage = (uint)Math.Clamp(brightness * 100, 0, 100);
+
+        foreach (var physicalMonitor in _physicalMonitors)
+        {
+            if (!NativeMethods.SetMonitorBrightness(physicalMonitor.Handle, brightnessPercentage))
+            {
+                Debug.WriteLine(
+                    $"Failed to set brightness on monitor #{physicalMonitor.Handle}. "
+                        + $"Error {Marshal.GetLastWin32Error()}."
+                );
+            }
+        }
+    }
+
     public void ResetGamma() => SetGamma(1, 1, 1);
 
     protected override void Dispose(bool disposing)
     {
+        if (_physicalMonitors.Any())
+        {
+            // This is a bit of a hack, but we need to convert the read-only list to an array
+            var physicalMonitorsArray = _physicalMonitors.ToArray();
+
+            if (
+                !NativeMethods.DestroyPhysicalMonitors(
+                    (uint)physicalMonitorsArray.Length,
+                    physicalMonitorsArray
+                )
+            )
+            {
+                Debug.WriteLine(
+                    "Failed to destroy physical monitors. "
+                        + $"Error {Marshal.GetLastWin32Error()}."
+                );
+            }
+        }
+
         // Don't reset gamma during dispose because this method is also called whenever
         // the device context gets invalidated.
         // Resetting gamma in such cases will cause unwanted flickering.
@@ -68,7 +109,10 @@ protected override void Dispose(bool disposing)
 
 public partial class DeviceContext
 {
-    public static DeviceContext? TryCreate(string deviceName)
+    public static DeviceContext? TryCreate(
+        string deviceName,
+        IReadOnlyList<PhysicalMonitor> physicalMonitors
+    )
     {
         var handle = NativeMethods.CreateDC(deviceName, deviceName, null, 0);
         if (handle == 0)
@@ -80,6 +124,6 @@ public partial class DeviceContext
             return null;
         }
 
-        return new DeviceContext(handle);
+        return new DeviceContext(handle, physicalMonitors);
     }
 }

LightBulb.PlatformInterop/Internal/NativeMethods.Dxva2.cs

@@ -0,0 +1,38 @@
+using System;
+using System.Runtime.InteropServices;
+
+namespace LightBulb.PlatformInterop.Internal;
+
+[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
+public struct PhysicalMonitor
+{
+    public nint Handle;
+
+    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
+    public string Description;
+}
+
+internal static partial class NativeMethods
+{
+    [DllImport("dxva2.dll", SetLastError = true)]
+    public static extern bool GetNumberOfPhysicalMonitorsFromHMONITOR(
+        nint hMonitor,
+        out uint pdwNumberOfPhysicalMonitors
+    );
+
+    [DllImport("dxva2.dll", SetLastError = true)]
+    public static extern bool GetPhysicalMonitorsFromHMONITOR(
+        nint hMonitor,
+        uint dwPhysicalMonitorArraySize,
+        [Out] PhysicalMonitor[] pPhysicalMonitorArray
+    );
+
+    [DllImport("dxva2.dll", SetLastError = true)]
+    public static extern bool SetMonitorBrightness(nint hMonitor, uint dwNewBrightness);
+
+    [DllImport("dxva2.dll", SetLastError = true)]
+    public static extern bool DestroyPhysicalMonitors(
+        uint dwPhysicalMonitorArraySize,
+        [In] PhysicalMonitor[] pPhysicalMonitorArray
+    );
+}

LightBulb.PlatformInterop/Monitor.cs

@@ -1,12 +1,42 @@
-using System.Collections.Generic;
+using System.Collections.Generic;
 using System.Diagnostics;
+using System.Linq;
 using System.Runtime.InteropServices;
 using LightBulb.PlatformInterop.Internal;
 
 namespace LightBulb.PlatformInterop;
 
 public partial class Monitor(nint handle) : NativeResource(handle)
 {
+    private PhysicalMonitor[]? TryGetPhysicalMonitors()
+    {
+        if (!NativeMethods.GetNumberOfPhysicalMonitorsFromHMONITOR(Handle, out var count))
+        {
+            Debug.WriteLine(
+                $"Failed to get physical monitor count for monitor #{Handle}. "
+                    + $"Error {Marshal.GetLastWin32Error()}."
+            );
+
+            return null;
+        }
+
+        if (count == 0)
+            return [];
+
+        var monitors = new PhysicalMonitor[count];
+        if (!NativeMethods.GetPhysicalMonitorsFromHMONITOR(Handle, count, monitors))
+        {
+            Debug.WriteLine(
+                $"Failed to get physical monitors for monitor #{Handle}. "
+                    + $"Error {Marshal.GetLastWin32Error()}."
+            );
+
+            return null;
+        }
+
+        return monitors;
+    }
+
     private MonitorInfoEx? TryGetMonitorInfo()
     {
         var monitorInfo = new MonitorInfoEx();
@@ -34,7 +64,11 @@ public partial class Monitor(nint handle) : NativeResource(handle)
         if (string.IsNullOrWhiteSpace(name))
             return null;
 
-        return DeviceContext.TryCreate(name);
+        var physicalMonitors = TryGetPhysicalMonitors();
+        if (physicalMonitors is null)
+            return null;
+
+        return DeviceContext.TryCreate(name, physicalMonitors);
     }
 
     protected override void Dispose(bool disposing) { }

LightBulb/Services/GammaService.cs

@@ -167,10 +167,12 @@ public void SetGamma(ColorConfiguration configuration)
         foreach (var deviceContext in _deviceContexts)
         {
             deviceContext.SetGamma(
-                GetRed(configuration) * configuration.Brightness,
-                GetGreen(configuration) * configuration.Brightness,
-                GetBlue(configuration) * configuration.Brightness
+                GetRed(configuration),
+                GetGreen(configuration),
+                GetBlue(configuration)
             );
+
+            deviceContext.SetBrightness(configuration.Brightness);
         }
 
         _isUpdatingGamma = false;