Fixed Windows 10 theme

src/app/dev/platforms/desktop/DevToys.Windows/Controls/MicaWindowWithOverlay.xaml.cs

@@ -1,4 +1,5 @@
-using System.Windows;
+using System.Runtime.InteropServices;
+using System.Windows;
 using System.Windows.Automation.Peers;
 using System.Windows.Automation.Provider;
 using System.Windows.Controls;
@@ -14,6 +15,7 @@
 using Windows.Win32.Foundation;
 using Windows.Win32.Graphics.Dwm;
 using Windows.Win32.UI.Controls;
+using Windows.Win32.UI.WindowsAndMessaging;
 using Application = System.Windows.Application;
 using Button = System.Windows.Controls.Button;
 using Color = System.Windows.Media.Color;
@@ -333,6 +335,36 @@ private void ApplyBackdrop(HWND windowHandle)
             int parameter = DwmValues.True;
             NativeMethods.SetWindowAttribute(windowHandle, (DWMWINDOWATTRIBUTE)DWMWINDOWATTRIBUTE_EXTENDED.DWMWA_MICA_EFFECT, ref parameter);
         }
+        else
+        {
+            uint gradientColor = 0xFF202020;
+            if (_themeListener.ActualAppTheme == ApplicationTheme.Light)
+            {
+                gradientColor = 0xFFFFFFFF;
+            }
+
+            // Effect for Windows 10
+            var accentPolicy = new AccentPolicy
+            {
+                AccentState = AccentState.ACCENT_ENABLE_ACRYLICBLURBEHIND,
+                GradientColor = gradientColor
+            };
+
+            int accentStructSize = Marshal.SizeOf(accentPolicy);
+            nint accentPtr = Marshal.AllocHGlobal(accentStructSize);
+            Marshal.StructureToPtr(accentPolicy, accentPtr, false);
+
+            var data = new WindowCompositionAttributeData
+            {
+                Attribute = WindowCompositionAttribute.WCA_ACCENT_POLICY,
+                SizeOfData = accentStructSize,
+                Data = accentPtr
+            };
+
+            NativeMethods.SetWindowCompositionAttribute(windowHandle, ref data);
+
+            Marshal.FreeHGlobal(accentPtr);
+        }
     }
 
     private void ApplyResizeBorderThickness()
@@ -393,14 +425,6 @@ private void UpdateTheme()
         dictionaries.Remove(resourceDictionaryToRemove);
         dictionaries.Add(resourceDictionary);
         UpdateLayout();
-
-        bool isWindow10_17763_OrLower = Environment.OSVersion.Version < new Version(10, 0, 17763);
-
-        // If Windows 10 17763 or lower
-        if (isWindow10_17763_OrLower)
-        {
-            // Todo: Based on the app theme, apply a Background color to the Window.
-        }
     }
 
     private nint ShowSnapLayout(nint lParam, ref bool handled)

src/app/dev/platforms/desktop/DevToys.Windows/Native/AccentEdges.cs

@@ -0,0 +1,10 @@
+namespace DevToys.Windows.Native;
+
+[Flags]
+internal enum AccentEdges
+{
+    Left = 0x20,
+    Top = 0x40,
+    Right = 0x80,
+    Bottom = 0x100
+}

src/app/dev/platforms/desktop/DevToys.Windows/Native/AccentPolicy.cs

@@ -0,0 +1,12 @@
+using System.Runtime.InteropServices;
+
+namespace DevToys.Windows.Native;
+
+[StructLayout(LayoutKind.Sequential)]
+internal struct AccentPolicy
+{
+    public AccentState AccentState;
+    public int AccentFlags;
+    public uint GradientColor;
+    public int AnimationId;
+}

src/app/dev/platforms/desktop/DevToys.Windows/Native/AccentState.cs

@@ -0,0 +1,11 @@
+namespace DevToys.Windows.Native;
+
+internal enum AccentState
+{
+    ACCENT_DISABLED = 0,
+    ACCENT_ENABLE_GRADIENT = 1,
+    ACCENT_ENABLE_TRANSPARENTGRADIENT = 2,
+    ACCENT_ENABLE_BLURBEHIND = 3,
+    ACCENT_ENABLE_ACRYLICBLURBEHIND = 4,
+    ACCENT_INVALID_STATE = 5
+}

src/app/dev/platforms/desktop/DevToys.Windows/Native/NativeMethods.cs

@@ -58,4 +58,14 @@ internal static void EnableMinimizeAndMaximizeCapabilities(HWND windowHandle)
         PInvoke.EnableMenuItem(systemMenuHandle, (uint)PInvoke.SC_MINIMIZE, MENU_ITEM_FLAGS.MF_BYCOMMAND | MENU_ITEM_FLAGS.MF_ENABLED);
 #pragma warning restore CA1416 // Validate platform compatibility
     }
+
+    /// <summary>
+    /// Sets various information regarding DWM window attributes
+    /// </summary>
+    /// <param name="hwnd">The window handle whose information is to be changed</param>
+    /// <param name="data">Pointer to a structure which both specifies and delivers the attribute data</param>
+    /// <returns>Nonzero on success, zero otherwise.</returns>
+    [DllImport("user32.dll")]
+    internal static extern int SetWindowCompositionAttribute(IntPtr hwnd, ref WindowCompositionAttributeData data);
+
 }

src/app/dev/platforms/desktop/DevToys.Windows/Native/WindowCompositionAttribute.cs

@@ -0,0 +1,6 @@
+namespace DevToys.Windows.Native;
+
+internal enum WindowCompositionAttribute
+{
+    WCA_ACCENT_POLICY = 19
+}

src/app/dev/platforms/desktop/DevToys.Windows/Native/WindowCompositionAttributeData.cs

@@ -0,0 +1,11 @@
+using System.Runtime.InteropServices;
+
+namespace DevToys.Windows.Native;
+
+[StructLayout(LayoutKind.Sequential)]
+internal struct WindowCompositionAttributeData
+{
+    public WindowCompositionAttribute Attribute;
+    public IntPtr Data;
+    public int SizeOfData;
+}