[GcodePreview]Fix background on dark theme (#29837)

src/modules/previewpane/GcodePreviewHandler/GcodePreviewHandlerControl.cs

@@ -29,6 +29,14 @@ namespace Microsoft.PowerToys.PreviewHandler.Gcode
         /// </summary>
         private bool _infoBarAdded;
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="GcodePreviewHandlerControl"/> class.
+        /// </summary>
+        public GcodePreviewHandlerControl()
+        {
+            SetBackgroundColor(Settings.BackgroundColor);
+        }
+
         /// <summary>
         /// Start the preview on the Control.
         /// </summary>
@@ -124,7 +132,7 @@ namespace Microsoft.PowerToys.PreviewHandler.Gcode
         {
             _pictureBox = new PictureBox();
             _pictureBox.BackgroundImage = image;
-            _pictureBox.BackgroundImageLayout = ImageLayout.Center;
+            _pictureBox.BackgroundImageLayout = Width >= image.Width && Height >= image.Height ? ImageLayout.Center : ImageLayout.Zoom;
             _pictureBox.Dock = DockStyle.Fill;
             Controls.Add(_pictureBox);
         }

src/modules/previewpane/GcodePreviewHandler/Settings.cs

@@ -0,0 +1,38 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace Microsoft.PowerToys.PreviewHandler.Gcode
+{
+    internal sealed class Settings
+    {
+        /// <summary>
+        /// Gets the color of the window background.
+        /// Even though this is not a setting yet, it's retrieved from a "Settings" class to be aligned with other preview handlers that contain this setting.
+        /// It's possible it can be converted into a setting in the future.
+        /// </summary>
+        public static Color BackgroundColor
+        {
+            get
+            {
+                if (GetTheme() == "dark")
+                {
+                    return Color.FromArgb(30, 30, 30); // #1e1e1e
+                }
+                else
+                {
+                    return Color.White;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Returns the theme.
+        /// </summary>
+        /// <returns>Theme that should be used.</returns>
+        public static string GetTheme()
+        {
+            return Common.UI.ThemeManager.GetWindowsBaseColor().ToLowerInvariant();
+        }
+    }
+}

src/modules/previewpane/GcodePreviewHandlerCpp/GcodePreviewHandler.cpp

@@ -1,5 +1,6 @@
 #include "pch.h"
 #include "GcodePreviewHandler.h"
+#include "../powerpreview/powerpreviewConstants.h"
 
 #include <shellapi.h>
 #include <Shlwapi.h>
@@ -9,6 +10,7 @@
 #include <common/logger/logger.h>
 #include <common/SettingsAPI/settings_helpers.h>
 #include <common/utils/process_path.h>
+#include <common/Themes/windows_colors.h>
 
 extern HINSTANCE g_hInst;
 extern long g_cDllRef;
@@ -202,6 +204,8 @@ IFACEMETHODIMP GcodePreviewHandler::Unload()
 
 IFACEMETHODIMP GcodePreviewHandler::SetBackgroundColor(COLORREF color)
 {
+    HBRUSH brush = CreateSolidBrush(WindowsColors::is_dark_mode() ? powerpreviewConstants::DARK_THEME_COLOR : powerpreviewConstants::LIGHT_THEME_COLOR);
+    SetClassLongPtr(m_hwndParent, GCLP_HBRBACKGROUND, reinterpret_cast<LONG_PTR>(brush));
     return S_OK;
 }
 

src/modules/previewpane/GcodePreviewHandlerCpp/GcodePreviewHandlerCpp.vcxproj

@@ -102,6 +102,9 @@
     <ProjectReference Include="..\..\..\common\SettingsAPI\SettingsAPI.vcxproj">
       <Project>{6955446d-23f7-4023-9bb3-8657f904af99}</Project>
     </ProjectReference>
+    <ProjectReference Include="..\..\..\common\Themes\Themes.vcxproj">
+      <Project>{98537082-0fdb-40de-abd8-0dc5a4269bab}</Project>
+    </ProjectReference>
   </ItemGroup>
   <Import Project="..\..\..\..\deps\spdlog.props" />
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />