settings: default SW rendering on Windows+ARM

Default to software GUI rendering on Windows on ARM.
Users can explicitly set the config to re-enable HW accelerated
rendering if they wish.

Author: mjcheetham

docs/configuration.md

@@ -247,6 +247,10 @@ git config --global credential.guiSoftwareRendering true
 
 Defaults to false (use hardware acceleration where available).
 
+> [!NOTE]
+> Windows on ARM devices defaults to using software rendering to work around a
+> known Avalonia issue: <https://github.com/AvaloniaUI/Avalonia/issues/10405>
+
 **Also see: [GCM_GUI_SOFTWARE_RENDERING][gcm-gui-software-rendering]**
 
 ---

docs/environment.md

@@ -294,6 +294,10 @@ export GCM_GUI_SOFTWARE_RENDERING=1
 
 Defaults to false (use hardware acceleration where available).
 
+> [!NOTE]
+> Windows on ARM devices defaults to using software rendering to work around a
+> known Avalonia issue: <https://github.com/AvaloniaUI/Avalonia/issues/10405>
+
 **Also see: [credential.guiSoftwareRendering][credential-guisoftwarerendering]**
 
 ---

src/shared/Core/PlatformUtils.cs

@@ -53,6 +53,22 @@ public static bool IsDevBox()
 #endif
         }
 
+        /// <summary>
+        /// Returns true if the current process is running on an ARM processor.
+        /// </summary>
+        /// <returns>True if ARM(v6,hf) or ARM64, false otherwise</returns>
+        public static bool IsArm()
+        {
+            switch (RuntimeInformation.OSArchitecture)
+            {
+                case Architecture.Arm:
+                case Architecture.Arm64:
+                    return true;
+                default:
+                    return false;
+            }
+        }
+
         public static bool IsWindowsBrokerSupported()
         {
             if (!IsWindows())

src/shared/Core/Settings.cs

@@ -568,10 +568,15 @@ public bool UseSoftwareRendering
         {
             get
             {
+                // WORKAROUND: Some Windows ARM devices have a graphics driver issue that causes transparent windows
+                // when using hardware rendering. Until this is fixed, we will default to software rendering on these
+                // devices. Users can always override this setting back to HW-accelerated rendering if they wish.
+                bool defaultValue = PlatformUtils.IsWindows() && PlatformUtils.IsArm();
+
                 return TryGetSetting(KnownEnvars.GcmGuiSoftwareRendering,
                     KnownGitCfg.Credential.SectionName,
                     KnownGitCfg.Credential.GuiSoftwareRendering,
-                        out string str) && str.ToBooleanyOrDefault(false);
+                    out string str) ? str.ToBooleanyOrDefault(defaultValue) : defaultValue;
             }
         }