Update gamma on all monitors directly

Fixes #100

LightBulb.WindowsApi/GammaManager.cs

@@ -1,25 +1,28 @@
 using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Windows.Forms;
 using LightBulb.WindowsApi.Internal;
 using LightBulb.WindowsApi.Models;
 
 namespace LightBulb.WindowsApi
 {
-    public class GammaManager : IDisposable
+    // This class doesn't use GetDC(IntPtr.Zero) to get DC for virtual screen because
+    // that doesn't work on Win10 with multi-monitor setup since v1903.
+    // https://github.com/Tyrrrz/LightBulb/issues/100
+    public partial class GammaManager : IDisposable
     {
         private readonly object _lock = new object();
-
-        private readonly IntPtr _window;
-        private readonly IntPtr _deviceContext;
+        private readonly IReadOnlyList<IntPtr> _deviceContextHandles;
 
         private int _gammaChannelOffset;
 
-        public GammaManager(IntPtr window)
+        public GammaManager(IReadOnlyList<IntPtr> deviceContextHandles)
         {
-            _window = window;
-            _deviceContext = NativeMethods.GetDC(window);
+            _deviceContextHandles = deviceContextHandles;
         }
 
-        public GammaManager() : this(NativeMethods.GetDesktopWindow())
+        public GammaManager() : this(GetDeviceContextHandlesForAllMonitors())
         {
         }
 
@@ -65,14 +68,25 @@ public void SetGamma(ColorBalance colorBalance)
                 var ramp = CreateGammaRamp(colorBalance);
 
                 // Set gamma
-                NativeMethods.SetDeviceGammaRamp(_deviceContext, ref ramp);
+                foreach (var hdc in _deviceContextHandles)
+                    NativeMethods.SetDeviceGammaRamp(hdc, ref ramp);
             }
         }
 
         public void Dispose()
         {
-            NativeMethods.ReleaseDC(_window, _deviceContext);
+            foreach (var hdc in _deviceContextHandles)
+                NativeMethods.DeleteDC(hdc);
+
             GC.SuppressFinalize(this);
         }
     }
+
+    public partial class GammaManager
+    {
+        private static IReadOnlyList<IntPtr> GetDeviceContextHandlesForAllMonitors() =>
+            Screen.AllScreens
+                .Select(s => NativeMethods.CreateDC(s.DeviceName, null, null, IntPtr.Zero))
+                .ToArray();
+    }
 }

LightBulb.WindowsApi/Internal/NativeMethods.cs

@@ -6,42 +6,42 @@
 namespace LightBulb.WindowsApi.Internal
 {
     [SuppressMessage("ReSharper", "InconsistentNaming")]
-    internal static class NativeMethods
+    internal static partial class NativeMethods
     {
-        [DllImport("user32.dll", EntryPoint = "GetDC", SetLastError = true)]
-        public static extern IntPtr GetDC(IntPtr hWnd);
-
-        [DllImport("user32.dll", EntryPoint = "ReleaseDC", SetLastError = true)]
-        public static extern int ReleaseDC(IntPtr hWnd, IntPtr hDC);
-
-        [DllImport("gdi32.dll", EntryPoint = "SetDeviceGammaRamp", SetLastError = true)]
-        public static extern bool SetDeviceGammaRamp(IntPtr hDC, ref GammaRamp lpRamp);
-
-        [DllImport("gdi32.dll", EntryPoint = "GetDeviceGammaRamp", SetLastError = true)]
-        public static extern bool GetDeviceGammaRamp(IntPtr hDC, out GammaRamp lpRamp);
-
         [DllImport("user32.dll", EntryPoint = "RegisterHotKey", SetLastError = true)]
-        public static extern bool RegisterHotKey(IntPtr hWnd, int id, int fsModifiers, int vk);
+        public static extern bool RegisterHotKey(IntPtr hwnd, int id, int fsModifiers, int vk);
 
         [DllImport("user32.dll", EntryPoint = "UnregisterHotKey", SetLastError = true)]
-        public static extern bool UnregisterHotKey(IntPtr hWnd, int id);
-
-        [DllImport("user32.dll", EntryPoint = "GetDesktopWindow", SetLastError = true)]
-        public static extern IntPtr GetDesktopWindow();
+        public static extern bool UnregisterHotKey(IntPtr hwnd, int id);
 
         [DllImport("user32.dll", EntryPoint = "GetForegroundWindow", SetLastError = true)]
         public static extern IntPtr GetForegroundWindow();
 
         [DllImport("user32.dll", EntryPoint = "GetWindowRect", SetLastError = true)]
-        public static extern bool GetWindowRect(IntPtr hWnd, out Rect lpRect);
+        public static extern bool GetWindowRect(IntPtr hwnd, out Rect lpRect);
 
         [DllImport("user32.dll", EntryPoint = "GetClientRect", SetLastError = true)]
-        public static extern bool GetClientRect(IntPtr hWnd, out Rect lpRect);
+        public static extern bool GetClientRect(IntPtr hwnd, out Rect lpRect);
 
         [DllImport("user32.dll", EntryPoint = "IsWindowVisible", SetLastError = true)]
-        public static extern bool IsWindowVisible(IntPtr hWnd);
+        public static extern bool IsWindowVisible(IntPtr hwnd);
 
         [DllImport("user32.dll", EntryPoint = "GetClassName", CharSet = CharSet.Unicode, SetLastError = true)]
-        public static extern int GetClassName(IntPtr hWnd, StringBuilder lpClassName, int nMaxCount);
+        public static extern int GetClassName(IntPtr hwnd, StringBuilder lpClassName, int nMaxCount);
+    }
+
+    internal static partial class NativeMethods
+    {
+        [DllImport("gdi32.dll", EntryPoint = "CreateDC", SetLastError = true)]
+        public static extern IntPtr CreateDC(string lpszDriver, string lpszDevice, string lpszOutput, IntPtr lpInitData);
+
+        [DllImport("gdi32.dll", EntryPoint = "DeleteDC", SetLastError = true)]
+        public static extern bool DeleteDC(IntPtr hdc);
+
+        [DllImport("gdi32.dll", EntryPoint = "GetDeviceGammaRamp", SetLastError = true)]
+        public static extern bool GetDeviceGammaRamp(IntPtr hdc, out GammaRamp lpRamp);
+
+        [DllImport("gdi32.dll", EntryPoint = "SetDeviceGammaRamp", SetLastError = true)]
+        public static extern bool SetDeviceGammaRamp(IntPtr hdc, ref GammaRamp lpRamp);
     }
 }