Changes to minimize the code changes required to the actual source files

Directory.Build.props

@@ -2,8 +2,9 @@
   <PropertyGroup>
     <RepositoryName>wpf</RepositoryName>
     <WindowsDesktopARM64Support>true</WindowsDesktopARM64Support>
-    <TargetFramework>net8.0</TargetFramework>
-    <TargetFrameworkVersion>8.0</TargetFrameworkVersion>
+    <TargetFramework>net481</TargetFramework>
+    <TargetFrameworkVersion>4.8.1</TargetFrameworkVersion>
+    <RunRefApiCompat>false</RunRefApiCompat>
   </PropertyGroup>
   <!-- Normalize $(TestWpfArcadeSdkPath) by appending a '\' to it if one is missing -->
   <PropertyGroup Condition="'$(TestWpfArcadeSdkPath)'!=''">
@@ -22,6 +23,11 @@
     <WpfArcadeSdkTargets>$(WpfArcadeSdkPath)Sdk\Sdk.targets</WpfArcadeSdkTargets>
   </PropertyGroup>
 
+  <ItemDefinitionGroup Condition="'$(TargetFrameworkIdentifier)'=='.NETFramework'">
+    <!-- We always want MSBuild properties generated that point at the restored location of each package. -->
+    <PackageReference GeneratePathProperty="true" />
+  </ItemDefinitionGroup>
+
   <Import Project="$(WpfArcadeSdkProps)"
           Condition="Exists('$(WpfArcadeSdkProps)') And Exists('$(WpfArcadeSdkTargets)')"/>
 

Directory.Build.targets

@@ -7,4 +7,35 @@
           Project="Sdk.targets"
           Condition="!Exists('$(WpfArcadeSdkProps)') Or !Exists('$(WpfArcadeSdkTargets)')"/>
 
+  <PropertyGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework' and '$(SignAssembly)' != 'false' and '$(PublicSign)' == 'true'">
+    <!-- Don't public sign .NETFramework assemblies -->
+    <DelaySign>true</DelaySign>
+    <PublicSign>false</PublicSign>
+  </PropertyGroup>
+
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)'=='.NETFramework'">
+    <PackageReference Include="$(SystemIOPackagingPackage)" Version="$(SystemIOPackagingVersion)" ExcludeAssets="compile" />
+    <PackageReference Include="$(SystemMemoryPackage)" Version="$(SystemMemoryPackageVersion)" />
+  </ItemGroup>
+
+  <Target Condition="'$(TargetFrameworkIdentifier)'=='.NETFramework'" Name="FixNetFxReferences" BeforeTargets="ResolveAssemblyReferences">
+    <ItemGroup>
+      <Reference Remove="WindowsBase" />
+      <Reference Remove="$(FrameworkPathOverride)\WindowsBase.dll" />
+      <Reference Remove="$(PkgSystem_IO_Packaging)\lib\net462\System.IO.Packaging.dll" />
+    </ItemGroup>
+    <ItemGroup>
+      <Reference Include="Accessibility" />
+      <Reference Include="System.IO.Compression" />
+      <Reference Include="System.Security" />
+      <Reference Include="System.Windows.Forms" />
+      <Reference Include="$(PkgSystem_IO_Packaging)\lib\netstandard2.0\System.IO.Packaging.dll" />
+    </ItemGroup>
+  </Target>
+
+  <Target Condition="'$(TargetFrameworkIdentifier)'=='.NETFramework'" Name="AliasNetFxReferences" AfterTargets="ResolveAssemblyReferences" BeforeTargets="CoreCompile">
+    <ItemGroup>
+      <ReferencePath Include="@(ReferencePath->WithMetadataValue('FileName', 'System'))" Aliases="System" />
+    </ItemGroup>
+  </Target>
 </Project>

eng/Versions.props

@@ -36,6 +36,7 @@
     <SystemDrawingCommonVersion>8.0.12</SystemDrawingCommonVersion>
     <SystemDirectoryServicesVersion>8.0.0</SystemDirectoryServicesVersion>
     <SystemIOPackagingVersion>8.0.1</SystemIOPackagingVersion>
+    <SystemMemoryPackageVersion>4.6.0</SystemMemoryPackageVersion>
     <SystemReflectionMetadataLoadContextVersion>8.0.1</SystemReflectionMetadataLoadContextVersion>
     <SystemReflectionTypeExtensionsPackageVersion>4.6.0-preview4.19176.11</SystemReflectionTypeExtensionsPackageVersion>
     <SystemResourcesExtensionsVersion>8.0.0</SystemResourcesExtensionsVersion>
@@ -95,6 +96,7 @@
     <SystemDirectoryServicesPackage>System.DirectoryServices</SystemDirectoryServicesPackage>
     <MicrosoftDotNetWpfDncEngPackage>Microsoft.DotNet.Wpf.DncEng</MicrosoftDotNetWpfDncEngPackage>
     <SystemIOPackagingPackage>System.IO.Packaging</SystemIOPackagingPackage>
+    <SystemMemoryPackage>System.Memory</SystemMemoryPackage>
     <SystemReflectionMetadataLoadContextPackage>System.Reflection.MetadataLoadContext</SystemReflectionMetadataLoadContextPackage>
   </PropertyGroup>
   <PropertyGroup>

eng/WpfArcadeSdk/tools/Wpf.Cpp.props

@@ -247,7 +247,8 @@
       <!--<AdditionalOptions>/Zc:twoPhase- %(AdditionalOptions)</AdditionalOptions>-->
       <!--<ConformanceMode>false</ConformanceMode>-->
 
-      <AdditionalOptions Condition="'$(ManagedCxx)'=='true'">%(AdditionalOptions) /clr:netcore /wd4956</AdditionalOptions>
+      <AdditionalOptions Condition="('$(ManagedCxx)'=='true') and ('$(TargetFramework)'!='net481')">%(AdditionalOptions) /clr:netcore /wd4956</AdditionalOptions>
+      <AdditionalOptions Condition="('$(ManagedCxx)'=='true') and ('$(TargetFramework)'=='net481')">%(AdditionalOptions) /wd4956</AdditionalOptions>
       <ShowIncludes Condition="'$(ShowIncludes)'=='true'">true</ShowIncludes>
     </ClCompile>
     <Link>

eng/WpfArcadeSdk/tools/Wpf.Cpp.targets

@@ -381,6 +381,15 @@ using namespace System::Runtime::Versioning;
       <Output ItemName="_NugetReferencesForCppCli" TaskParameter="Result" />
     </FilterItem1ByItem2>
   </Target>
+  <Target
+    Name="GetPackagePathProperties"
+    Returns="%40(NugetPackagePaths)">
+    <ItemGroup>
+      <NugetPackagePaths Include="PkgSystem_IO_Packaging">
+        <Value>%24(PkgSystem_IO_Packaging)</Value>
+      </NugetPackagePaths>
+    </ItemGroup>
+  </Target>
   <ItemGroup>
     <NugetReferencesForCppCli Include="%40(_NugetReferencesForCppCli->'%25(OriginalItemSpec)')" />
   </ItemGroup>
@@ -410,11 +419,24 @@ using namespace System::Runtime::Versioning;
       </ProjectToBuild>
     </ItemGroup>
     <MSBuild Projects="@(ProjectToBuild)"
-             Targets="Restore;ResolveReferences;IdentifyNugetReferences"
+             Targets="Restore"
+             Properties="TargetFramework=$(TargetFramework);Platform=$(Architecture);RuntimeIdentifier=win-$(Architecture);ForceEvalOnNextMsBuild=true" />
+
+    <MSBuild Projects="@(ProjectToBuild)"
+             Targets="ResolveReferences;IdentifyNugetReferences;GetPackagePathProperties"
              Properties="TargetFramework=$(TargetFramework);Platform=$(Architecture);RuntimeIdentifier=win-$(Architecture)">
-      <Output  TaskParameter="TargetOutputs" ItemName="NugetReferencesForCppCli" />
+      <Output TaskParameter="TargetOutputs" ItemName="MixedTargetOutputs" />
     </MSBuild>
 
+    <ItemGroup>
+      <NugetReferencesForCppCli Condition="'%(MixedTargetOutputs.MSBuildSourceTargetName)'=='ResolveReferences'" Include="@(MixedTargetOutputs)" />
+      <NugetPackagePaths Condition="'%(MixedTargetOutputs.MSBuildSourceTargetName)'=='GetPackagePathProperties'" Include="@(MixedTargetOutputs)" />
+    </ItemGroup>
+
+    <CreateProperty Value="%(NugetPackagePaths.Value)">
+      <Output TaskParameter="Value" PropertyName="%(NugetPackagePaths.Identity)" />
+    </CreateProperty>
+
     <!--
       Add the newly discovered list of .NET core references to $(AdditionalExplicitAssemblyReferences)
     -->

packaging/Microsoft.NET.Sdk.WindowsDesktop/Microsoft.NET.Sdk.WindowsDesktop.ArchNeutral.csproj

@@ -28,6 +28,6 @@
   </ItemGroup>
 
   <!-- Windows Forms validation and packaging -->
-  <Import Project="Microsoft.NET.Sdk.WindowsDesktop.WinForms.Packaging.targets" />
+  <Import Condition="$(TargetFramework.StartsWith('net4'))!='true'" Project="Microsoft.NET.Sdk.WindowsDesktop.WinForms.Packaging.targets" />
 
 </Project>

src/Microsoft.DotNet.Wpf/src/DirectWriteForwarder/DirectWriteForwarder.vcxproj

@@ -29,17 +29,20 @@
   <PropertyGroup>
     <UseDestinationLibFolder>true</UseDestinationLibFolder>
     <TargetFrameworkIdentifier>.NETCoreApp</TargetFrameworkIdentifier>
+    <TargetFrameworkIdentifier Condition="$(TargetFramework.StartsWith('net4'))!='true'">.NETFramework</TargetFrameworkIdentifier>
     <RestoreProjectStyle>Unknown</RestoreProjectStyle>
-    <!-- 
+    <!--
       Opting out of this to ensure _WindowsBaseReference is used as 
       OutputItemsType in the project reference later.
     -->
     <LegacyNativeReferenceResolution>true</LegacyNativeReferenceResolution>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
   <PropertyGroup>
-    <Keyword>NetCoreCProj</Keyword>
-    <CLRSupport>pure</CLRSupport>
+    <Keyword Condition="'$(TargetFrameworkIdentifier)'!='.NETFramework'">NetCoreCProj</Keyword>
+    <Keyword Condition="'$(TargetFrameworkIdentifier)'=='.NETFramework'">ManagedCProj</Keyword>
+    <CLRSupport Condition="'$(TargetFrameworkIdentifier)'!='.NETFramework'">pure</CLRSupport>
+    <CLRSupport Condition="'$(TargetFrameworkIdentifier)'=='.NETFramework'">true</CLRSupport>
     <WindowsTargetPlatformVersion>10.0</WindowsTargetPlatformVersion>
     <ConfigurationType>DynamicLibrary</ConfigurationType>
   </PropertyGroup>
@@ -89,7 +92,7 @@
   <!--
     PackageReferences to pass to CppCliHelper target
   -->
-  <ItemGroup>
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)'!='.NETFramework'">
     <AdditionalPackageReference Include="$(SystemIOPackagingPackage)" Version="$(SystemIOPackagingVersion)" />
   </ItemGroup>
   <!--

src/Microsoft.DotNet.Wpf/src/PresentationBuildTasks/PresentationBuildTasks.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>net472;net8.0</TargetFrameworks>
+    <TargetFrameworks>net472;net481;net8.0</TargetFrameworks>
     <EnableDefaultItems>false</EnableDefaultItems>
     <EnablePInvokeAnalyzer>true</EnablePInvokeAnalyzer>
 
@@ -51,7 +51,7 @@
   <!--
     Limit the assemblies that are packaged into Microsoft.NET.Sdk.WindowsDesktop
   -->
-  <ItemGroup Condition="'$(TargetFramework)'=='net472'">
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)'=='.NETFramework'">
     <PackagingAssemblyContent Include="PresentationBuildTasks.dll" />
     <PackagingAssemblyContent Include="System.Collections.Immutable.dll" />
     <PackagingAssemblyContent Include="System.Memory.dll" />

src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/DpiUtil/DpiUtil+ProcessDpiAwarenessHelper.cs

@@ -2,10 +2,17 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#if NETFX
+extern alias System;
+#endif
 
 namespace MS.Internal
 {
+#if NETFX
+    using System::Microsoft.Win32.SafeHandles;
+#else
     using Microsoft.Win32.SafeHandles;
+#endif
     using MS.Win32;
     using System;
     using System.Diagnostics;

src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/FontCache/FontCacheUtil.cs

@@ -661,7 +661,11 @@ private static string NormalizeFontFamilyReference(string fontFamilyReference, i
             {
                 // No fragment separator. The entire string is a family name so convert to uppercase
                 // and add a fragment separator at the beginning.
+#if NETFX
+                return string.Concat("#", fontFamilyReference.Substring(startIndex, length)).ToUpperInvariant();
+#else
                 return string.Concat("#", fontFamilyReference.AsSpan(startIndex, length)).ToUpperInvariant();
+#endif
             }
             else if (fragmentIndex + 1 == startIndex + length)
             {

src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/IO/Packaging/ByteRangeDownloader.cs

@@ -797,9 +797,13 @@ static private bool CheckContentRange(WebHeaderCollection responseHeaders, int b
             }
 
             // Get the first byte offset of the range (XXX)
-            int firstByteOffset = Int32.Parse(contentRange.AsSpan(ByteRangeUnit.Length,
-                                                                        index - ByteRangeUnit.Length),
-                                                NumberStyles.None, NumberFormatInfo.InvariantInfo);
+            int firstByteOffset = Int32.Parse(
+#if NETFX
+                contentRange.Substring(ByteRangeUnit.Length, index - ByteRangeUnit.Length),
+#else
+                contentRange.AsSpan(ByteRangeUnit.Length, index - ByteRangeUnit.Length),
+#endif
+                NumberStyles.None, NumberFormatInfo.InvariantInfo);
 
             ReadOnlySpan<char> contentRangeSpan = contentRange.AsSpan(index + 1);
             // ContentRange: YYY/ZZZ
@@ -811,7 +815,13 @@ static private bool CheckContentRange(WebHeaderCollection responseHeaders, int b
             }
 
             // Get the last byte offset of the range (YYY)
-            int lastByteOffset = Int32.Parse(contentRangeSpan.Slice(0, index), NumberStyles.None, NumberFormatInfo.InvariantInfo);
+            int lastByteOffset = Int32.Parse(
+#if NETFX
+                contentRangeSpan.Slice(0, index).ToString(),
+#else
+                contentRangeSpan.Slice(0, index),
+#endif
+                NumberStyles.None, NumberFormatInfo.InvariantInfo);
 
             // Get the instance length
             // ContentRange: ZZZ
@@ -822,7 +832,13 @@ static private bool CheckContentRange(WebHeaderCollection responseHeaders, int b
                 //  if it is not an integer or the integer is bigger than Int32 since HttpWebRequest.AddRange
                 //  only supports Int32
                 //  Once HttpWebRequest.AddRange start supporting Int64 we should change it to Int64 and long
-                Int32.Parse(contentRangeSpan, NumberStyles.None, NumberFormatInfo.InvariantInfo);
+                Int32.Parse(
+#if NETFX
+                    contentRangeSpan.ToString(),
+#else
+                    contentRangeSpan,
+#endif
+                    NumberStyles.None, NumberFormatInfo.InvariantInfo);
             }
 
             // The response is considered to be successful if

src/Microsoft.DotNet.Wpf/src/PresentationCore/PresentationCore.csproj

@@ -1360,6 +1360,13 @@
     <Compile Include="System\Windows\Resources\AssemblyAssociatedContentFileAttribute.cs" />
   </ItemGroup>
 
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)'=='.NETFramework'">
+    <Compile Include="$(WpfSharedDir)\OtherAssemblyAttrs.Global.cs" />
+    <Compile Include="$(WpfSharedDir)\System\DictionaryHelpers.cs" />
+    <Compile Include="$(WpfSharedDir)\System\InternalArgumentNullException.cs" />
+    <Compile Include="$(WpfSharedDir)\System\ReferenceEqualityComparer.cs" />
+  </ItemGroup>
+
   <ItemGroup>
     <NetCoreReference Include="Microsoft.Win32.Primitives" />
     <NetCoreReference Include="Microsoft.Win32.Registry" />
@@ -1405,8 +1412,8 @@
 
   <ItemGroup>
     <PackageReference Include="System.Configuration.ConfigurationManager" Version="$(SystemConfigurationConfigurationManagerPackageVersion)" />
-    <PackageReference Include="System.Windows.Extensions" Version="$(SystemWindowsExtensionsPackageVersion)" />
-    <PackageReference Include="$(SystemIOPackagingPackage)" Version="$(SystemIOPackagingVersion)" />
+    <PackageReference Condition="'$(TargetFrameworkIdentifier)'!='.NETFramework'" Include="System.Windows.Extensions" Version="$(SystemWindowsExtensionsPackageVersion)" />
+    <PackageReference Condition="'$(TargetFrameworkIdentifier)'!='.NETFramework'" Include="$(SystemIOPackagingPackage)" Version="$(SystemIOPackagingVersion)" />
   </ItemGroup>
 
   <ItemGroup>

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/InputScopeConverter.cs

@@ -120,7 +120,11 @@ public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo c
 
                 if (!spanSource.IsEmpty)
                 {
+#if NETFX
+                    sn = (InputScopeNameValue)Enum.Parse(typeof(InputScopeNameValue), spanSource.ToString());
+#else
                     sn = Enum.Parse<InputScopeNameValue>(spanSource);
+#endif
                 }
             }
 

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Animation/KeyTimeConverter.cs

@@ -189,7 +189,11 @@ public override object ConvertTo(
                                     keyTime.Percent * 100.0,
                                     destinationType);
 
+#if NETFX
+                            return string.Concat(returnValue, "%");
+#else
                             return string.Concat(returnValue, (ReadOnlySpan<char>)stackalloc char[] { '%' });
+#endif
 
                         case KeyTimeType.TimeSpan:
 

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/CharacterMetrics.cs

@@ -169,7 +169,11 @@ private static double[] ParseMetrics(string s)
                     // Non-empty field; convert it to double.
                     ReadOnlySpan<char> field = s.AsSpan(i, k - i);
                     if (!double.TryParse(
+#if NETFX
+                        field.ToString(),
+#else
                         field,
+#endif
                         NumberStyles.AllowDecimalPoint | NumberStyles.AllowLeadingSign,
                         System.Windows.Markup.TypeConverterHelper.InvariantEnglishUS,
                         out metrics[fieldIndex]

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Color.cs

@@ -279,7 +279,11 @@ internal string ConvertToString(string format, IFormatProvider provider)
             {
                 if (format == null)
                 {
+#if NETFX
+                    return $"#{this.sRgbColor.a:X2}{this.sRgbColor.r:X2}{this.sRgbColor.g:X2}{this.sRgbColor.b:X2}";
+#else
                     return string.Create(provider, stackalloc char[128], $"#{this.sRgbColor.a:X2}{this.sRgbColor.r:X2}{this.sRgbColor.g:X2}{this.sRgbColor.b:X2}");
+#endif
                 }
                 else
                 {

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/UniqueEventHelper.cs

@@ -7,6 +7,10 @@
 
 namespace System.Windows.Media
 {
+#if NETFX
+    using ArgumentNullException = System.Xaml.ArgumentNullException;
+#endif
+
     /// <summary>
     /// Aids in making events unique. i.e. you register the same function for
     /// the same event twice, but it will only be called once for each time

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Navigation/BaseUriHelper.cs

@@ -643,7 +643,11 @@ private static byte[] ParseAssemblyKey(string assemblyKey)
                 byte[] keyToken = new byte[byteCount];
                 for (int i = 0; i < byteCount; i++)
                 {
+#if NETFX
+                    keyToken[i] = byte.Parse(assemblyKey.Substring(i * 2, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture);
+#else
                     keyToken[i] = byte.Parse(assemblyKey.AsSpan(i * 2, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture);
+#endif
                 }
 
                 return keyToken;

src/Microsoft.DotNet.Wpf/src/PresentationCore/ref/PresentationCore-ref.csproj

@@ -11,7 +11,6 @@
     <GenerateResourcesSRNamespace>MS.Internal.PresentationCore</GenerateResourcesSRNamespace>
     <ResolveAssemblyWarnOrErrorOnTargetArchitectureMismatch>None</ResolveAssemblyWarnOrErrorOnTargetArchitectureMismatch>
     <Platforms>AnyCPU;x64;arm64</Platforms>
-
   </PropertyGroup>
 
   <ItemGroup>
@@ -63,8 +62,8 @@
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="System.Configuration.ConfigurationManager" Version="$(SystemConfigurationConfigurationManagerPackageVersion)" />
-    <PackageReference Include="System.Windows.Extensions" Version="$(SystemWindowsExtensionsPackageVersion)" />
-    <PackageReference Include="$(SystemIOPackagingPackage)" Version="$(SystemIOPackagingVersion)" />
+    <PackageReference Condition="'$(TargetFrameworkIdentifier)'!='.NETFramework'" Include="System.Windows.Extensions" Version="$(SystemWindowsExtensionsPackageVersion)" />
+    <PackageReference Condition="'$(TargetFrameworkIdentifier)'!='.NETFramework'" Include="$(SystemIOPackagingPackage)" Version="$(SystemIOPackagingVersion)" />
   </ItemGroup>
   <ItemGroup>
     <!-- required for internals access -->