Merge pull request #12726 from AvaloniaUI/win32_dpi_awareness_option

Add win32 platform options to select process DPI awareness

src/Windows/Avalonia.Win32/Win32Platform.cs

@@ -49,7 +49,6 @@ namespace Avalonia.Win32
 
         public Win32Platform()
         {
-            SetDpiAwareness();
             CreateMessageWindow();
             _dispatcher = new Win32DispatcherImpl(_hwnd);
         }
@@ -80,6 +79,9 @@ namespace Avalonia.Win32
         public static void Initialize(Win32PlatformOptions options)
         {
             s_options = options;
+
+            SetDpiAwareness();
+
             var renderTimer = options.ShouldRenderOnUIThread ? new UiThreadRenderTimer(60) : new DefaultRenderTimer(60);
 
             AvaloniaLocator.CurrentMutable
@@ -264,12 +266,31 @@ namespace Avalonia.Win32
             var user32 = LoadLibrary("user32.dll");
             var method = GetProcAddress(user32, nameof(SetProcessDpiAwarenessContext));
 
+            var dpiAwareness = Options.DpiAwareness;
+
             if (method != IntPtr.Zero)
             {
-                if (SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2) ||
+                if (dpiAwareness == Win32DpiAwareness.Unaware)
-                    SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE))
                 {
-                    return;
+                    if (SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_UNAWARE))
+                    {
+                        return;
+                    }
+                }
+                else if (dpiAwareness == Win32DpiAwareness.SystemDpiAware)
+                {
+                    if (SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_SYSTEM_AWARE))
+                    {
+                        return;
+                    }
+                }
+                else if (dpiAwareness == Win32DpiAwareness.PerMonitorDpiAware)
+                {
+                    if (SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2) ||
+                    SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE))
+                    {
+                        return;
+                    }
                 }
             }
 
@@ -278,11 +299,20 @@ namespace Avalonia.Win32
 
             if (method != IntPtr.Zero)
             {
-                SetProcessDpiAwareness(PROCESS_DPI_AWARENESS.PROCESS_PER_MONITOR_DPI_AWARE);
+                var awareness = (dpiAwareness) switch
+                {
+                    Win32DpiAwareness.Unaware => PROCESS_DPI_AWARENESS.PROCESS_DPI_UNAWARE,
+                    Win32DpiAwareness.SystemDpiAware => PROCESS_DPI_AWARENESS.PROCESS_SYSTEM_DPI_AWARE,
+                    Win32DpiAwareness.PerMonitorDpiAware => PROCESS_DPI_AWARENESS.PROCESS_PER_MONITOR_DPI_AWARE,
+                    _ => PROCESS_DPI_AWARENESS.PROCESS_PER_MONITOR_DPI_AWARE,
+                };
+
+                SetProcessDpiAwareness(awareness);
                 return;
             }
 
-            SetProcessDPIAware();
+            if (dpiAwareness != Win32DpiAwareness.Unaware)
+                SetProcessDPIAware();
         }
     }
 }

src/Windows/Avalonia.Win32/Win32PlatformOptions.cs

@@ -25,6 +25,27 @@ public enum Win32RenderingMode
     Wgl = 3
 }
 
+/// <summary>
+/// Represents the DPI Awareness for the application.
+/// </summary>
+public enum Win32DpiAwareness
+{
+    /// <summary>
+    /// The application is DPI unaware.
+    /// </summary>
+    Unaware,
+
+    /// <summary>
+    /// The application is system DPI aware. It will query DPI once and will not adjust to new DPI changes
+    /// </summary>
+    SystemDpiAware,
+
+    /// <summary>
+    /// The application is per-monitor DPI aware. It adjust its scale factor whenever DPI changes.
+    /// </summary>
+    PerMonitorDpiAware
+}
+
 /// <summary>
 /// Represents the Win32 window composition mode.
 /// </summary>
@@ -137,4 +158,9 @@ public class Win32PlatformOptions
     /// and <see cref="CompositionMode"/> only accepts null or <see cref="Win32CompositionMode.RedirectionSurface"/>.
     /// </summary>
     public IPlatformGraphics? CustomPlatformGraphics { get; set; }
+
+    /// <summary>
+    /// Gets or sets the application's DPI awareness.
+    /// </summary>
+    public Win32DpiAwareness DpiAwareness { get; set; } = Win32DpiAwareness.PerMonitorDpiAware;
 }