Add internal render resolution scale and fix DPI Issue (#468)

* Add internal render resolution scale and fix embedded surface DPI scaling

Adds a GUI-configurable internal resolution scale (Graphics tab) that
renders offscreen color/depth targets below native guest resolution
and upscales on present, trading image quality for GPU headroom.
Storage/UAV images and sampled asset textures are left untouched, and
texture-alias/feedback-loop lookups compare against each target's
logical (unscaled) size so scaled render targets are still found
correctly when sampled back.

Also fixes the embedded game surface not filling the window: the
isolated emulator child process had no declared DPI awareness, so
Windows silently downscaled every window-geometry query it made
against the GUI-owned surface HWND by the display's DPI factor,
leaving an unfilled black margin on scaled displays.

* Remove flaky Gen5ScalarMemoryFallbackTests

* Restore Gen5ScalarMemoryFallbackTests

---------

Co-authored-by: Spooks4576 <Spooks4576@users.noreply.github.com>

src/SharpEmu.GUI/GameSurfaceHost.cs

@@ -351,6 +351,13 @@ public sealed class GameSurfaceHost : NativeControlHost
         var width = Math.Max(1, (int)Math.Round(Bounds.Width * renderScale));
         var height = Math.Max(1, (int)Math.Round(Bounds.Height * renderScale));
         var sizeChanged = _surface.PixelWidth != width || _surface.PixelHeight != height;
+        if (Environment.GetEnvironmentVariable("SHARPEMU_TRACE_SURFACE_SIZE") == "1")
+        {
+            Console.Error.WriteLine(
+                $"[GUI][TRACE] GameSurfaceHost.UpdateSurfaceSize bounds={Bounds.Width}x{Bounds.Height} " +
+                $"scale={renderScale} computed={width}x{height} changed={sizeChanged} " +
+                $"prevSurface={_surface.PixelWidth}x{_surface.PixelHeight}");
+        }
         _surface.UpdatePixelSize(width, height);
 
         if (!sizeChanged)

src/SharpEmu.GUI/GuiSettings.cs

@@ -53,6 +53,9 @@ public sealed class GuiSettings
     /// <summary>Names of SHARPEMU_* switches set to "1" in the emulator's environment at launch.</summary>
     public List<string> EnvironmentToggles { get; set; } = new();
 
+    /// <summary>Internal render resolution scale (1.0 = native, 0.5 = half).</summary>
+    public double RenderResolutionScale { get; set; } = 1.0;
+
     /// <summary>
     /// Discord application ID used for Rich Presence; the default is the
     /// SharpEmu application. Override to rebrand what Discord shows as
@@ -96,6 +99,10 @@ public sealed class GuiSettings
         settings.LogLevel ??= "Info";
         settings.Language ??= "en";
         settings.DiscordClientId ??= "1525606762248540221";
+        if (settings.RenderResolutionScale <= 0 || settings.RenderResolutionScale > 2.0)
+        {
+            settings.RenderResolutionScale = 1.0;
+        }
 
         return settings;
     }

src/SharpEmu.GUI/MainWindow.axaml

@@ -400,6 +400,29 @@ SPDX-License-Identifier: GPL-2.0-or-later
                 </StackPanel>
               </ScrollViewer>
             </TabItem>
+            <TabItem x:Name="GraphicsTabItem" Header="Graphics" FontSize="15">
+              <ScrollViewer>
+                <StackPanel Margin="0,14,0,16" Spacing="16" MaxWidth="1280" HorizontalAlignment="Left">
+
+                  <Border Classes="card">
+                    <StackPanel Spacing="14">
+                      <TextBlock x:Name="RenderingSectionTitle" Classes="sectionTitle" Text="RENDERING" />
+
+                      <local:SettingRow x:Name="RenderResolutionRow" Label="Internal resolution"
+                                        Description="Render offscreen targets below native resolution and upscale on present. Lower values trade image quality for GPU headroom; takes effect on next launch.">
+                        <ComboBox x:Name="RenderResolutionBox" Width="160" SelectedIndex="0"
+                                  VerticalAlignment="Center" CornerRadius="8">
+                          <ComboBoxItem x:Name="RenderResolution100Item" Content="100% (native)" Tag="1.0" />
+                          <ComboBoxItem x:Name="RenderResolution75Item" Content="75%" Tag="0.75" />
+                          <ComboBoxItem x:Name="RenderResolution50Item" Content="50%" Tag="0.5" />
+                          <ComboBoxItem x:Name="RenderResolution25Item" Content="25%" Tag="0.25" />
+                        </ComboBox>
+                      </local:SettingRow>
+                    </StackPanel>
+                  </Border>
+                </StackPanel>
+              </ScrollViewer>
+            </TabItem>
             <TabItem x:Name="EnvTabItem" Header="Environment" FontSize="15">
               <ScrollViewer>
                 <StackPanel Margin="0,14,0,16" Spacing="16" MaxWidth="1280" HorizontalAlignment="Left">

src/SharpEmu.GUI/MainWindow.axaml.cs

@@ -192,6 +192,18 @@ public partial class MainWindow : Window
         // it is open already uses the new values.
         LogLevelBox.SelectionChanged += (_, _) => _settings.LogLevel = SelectedLogLevel();
         TraceImportsBox.ValueChanged += (_, _) => _settings.ImportTraceLimit = (int)(TraceImportsBox.Value ?? 0);
+        RenderResolutionBox.SelectionChanged += (_, _) =>
+        {
+            if (RenderResolutionBox.SelectedItem is ComboBoxItem { Tag: string tag } &&
+                double.TryParse(
+                    tag,
+                    System.Globalization.NumberStyles.Float,
+                    System.Globalization.CultureInfo.InvariantCulture,
+                    out var scale))
+            {
+                _settings.RenderResolutionScale = scale;
+            }
+        };
         StrictToggle.IsCheckedChanged += (_, _) => _settings.StrictDynlibResolution = StrictToggle.IsChecked == true;
         LogToFileToggle.IsCheckedChanged += (_, _) => _settings.LogToFile = LogToFileToggle.IsChecked == true;
         OverrideLogFileToggle.IsCheckedChanged += (_, _) =>
@@ -869,6 +881,13 @@ public partial class MainWindow : Window
             _ => 2,
         };
         TraceImportsBox.Value = Math.Clamp(_settings.ImportTraceLimit, 0, 4096);
+        RenderResolutionBox.SelectedIndex = _settings.RenderResolutionScale switch
+        {
+            >= 0.875 => 0,
+            >= 0.625 => 1,
+            >= 0.375 => 2,
+            _ => 3,
+        };
         StrictToggle.IsChecked = _settings.StrictDynlibResolution;
         LogToFileToggle.IsChecked = _settings.LogToFile;
         OverrideLogFileToggle.IsChecked = _settings.OverrideLogFile;
@@ -1788,6 +1807,12 @@ public partial class MainWindow : Window
             _appliedEnvironmentVariables.Add(name);
         }
 
+        Environment.SetEnvironmentVariable(
+            "SHARPEMU_RENDER_SCALE",
+            _settings.RenderResolutionScale.ToString(
+                "0.###",
+                System.Globalization.CultureInfo.InvariantCulture));
+
         if (SharpEmuLog.TryParseLevel(effective.LogLevel, out var logLevel))
         {
             SharpEmuLog.MinimumLevel = logLevel;
@@ -2030,8 +2055,6 @@ public partial class MainWindow : Window
                 RestoreGameViewToFull();
                 GameView.Background = Brushes.Black;
                 GameView.IsHitTestVisible = true;
-                _gameSurfaceHost?.SetPresentationVisible(true);
-                _gameSurfaceHost?.SetCursorAutoHide(true);
                 LibraryPage.IsVisible = false;
                 OptionsPage.IsVisible = false;
                 LibraryToolbar.IsVisible = false;
@@ -2040,6 +2063,19 @@ public partial class MainWindow : Window
                 LaunchBar.IsVisible = false;
                 HideSessionLoading();
                 UpdateSessionBarVisibility();
+
+                // Defer so the layout pass from the margin change above settles first.
+                Dispatcher.UIThread.Post(() =>
+                {
+                    if (!_isRunning || _isStopping)
+                    {
+                        return;
+                    }
+
+                    _gameSurfaceHost?.RefreshSurfaceSize();
+                    _gameSurfaceHost?.SetPresentationVisible(true);
+                    _gameSurfaceHost?.SetCursorAutoHide(true);
+                });
             }
         });
     }