Light/Dark themer added for Winform title bar

MainForm.cs

@@ -13,7 +13,7 @@ using CefSharp.WinForms;
 
 namespace VRCX
 {
-    public partial class MainForm : Form
+    public partial class MainForm : WinformBase
     {
         public static MainForm Instance;
         public ChromiumWebBrowser Browser;

VRCX.csproj

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
   <PropertyGroup>
@@ -119,6 +119,10 @@
     <Compile Include="VRCXStorage.cs" />
     <Compile Include="JsonSerializer.cs" />
     <Compile Include="WinApi.cs" />
+    <Compile Include="WinformBase.cs">
+      <SubType>Form</SubType>
+    </Compile>
+    <Compile Include="WinformThemer.cs" />
     <EmbeddedResource Include="VRForm.resx">
       <DependentUpon>VRForm.cs</DependentUpon>
     </EmbeddedResource>

VRForm.cs

@@ -10,7 +10,7 @@ using CefSharp.WinForms;
 
 namespace VRCX
 {
-    public partial class VRForm : Form
+    public partial class VRForm : WinformBase
     {
         public static VRForm Instance;
         private ChromiumWebBrowser _browser1;

WinformBase.cs

@@ -0,0 +1,19 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows.Forms;
+
+namespace VRCX
+{
+    public class WinformBase : Form
+    {
+        protected override void OnHandleCreated(EventArgs e)
+        {
+            WinformThemer.SetThemeToGlobal(this);
+            base.OnHandleCreated(e);
+        }
+    }
+}

WinformThemer.cs

@@ -0,0 +1,77 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows.Forms;
+
+namespace VRCX
+{
+    //Based off DWMWA_USE_IMMERSIVE_DARK_MODE, documentation: https://docs.microsoft.com/en-us/windows/win32/api/dwmapi/ne-dwmapi-dwmwindowattribute
+    //dwAttribute was 19 before Windows 20H1, 20 after Windows 20H1
+
+    internal static class WinformThemer
+    {
+        [DllImport("DwmApi")]
+        private static extern int DwmSetWindowAttribute(IntPtr hwnd, int dwAttribute, int[] pvAttribute, int cbAttribute);
+
+        [DllImport("DwmApi")]
+        private static extern int DwmGetWindowAttribute(IntPtr hwnd, int dwAttribute, IntPtr pvAttribute, int cbAttribute);
+
+        private static int currentTheme = 0;
+
+        /// <summary>
+        /// Sets the global theme of the app
+        /// Light = 0
+        /// Dark = 1
+        /// </summary>
+        public static void SetGlobalTheme(int theme)
+        {
+            currentTheme = theme;
+            foreach (Form form in Application.OpenForms)
+            {
+                SetThemeToGlobal(form);
+            }
+        }
+
+        /// <summary>
+        /// Gets the global theme of the app
+        /// Light = 0
+        /// Dark = 1
+        /// </summary>
+        public static int GetGlobalTheme() => currentTheme;
+
+        public static void SetThemeToGlobal(Form form)
+        {
+            SetThemeToGlobal(form.Handle);
+        }
+
+        private static void SetThemeToGlobal(IntPtr handle)
+        {
+            if (GetTheme(handle) != currentTheme)
+            {
+                if (DwmSetWindowAttribute(handle, 19, new[] { currentTheme }, 4) != 0)
+                    DwmSetWindowAttribute(handle, 20, new[] { currentTheme }, 4);
+            }
+        }
+
+        private static int GetTheme(IntPtr handle)
+        {
+            //Allocate needed memory
+            IntPtr curThemePtr = Marshal.AllocHGlobal(4);
+
+            //See what window state it currently is
+            if (DwmGetWindowAttribute(handle, 19, curThemePtr, 4) != 0)
+                DwmGetWindowAttribute(handle, 20, curThemePtr, 4);
+
+            //Read current theme (light = 0, dark = 1)
+            int theme = Marshal.ReadInt32(curThemePtr);
+
+            //Free previously allocated
+            Marshal.FreeHGlobal(curThemePtr);
+
+            return theme;
+        }
+    }
+}