[Extensibility] Resizetizer: Enable external backend processing

src/SingleProject/Resizetizer/src/DpiPath.cs

@@ -312,9 +312,34 @@ public static DpiPath[] SplashScreen
 
 		}
 
+		public static class Generic
+		{
+			public static DpiPath Original =>
+				new DpiPath("", 1.0m);
+
+			public static DpiPath[] Image
+				=> new[]
+				{
+					new DpiPath("", 1.0m),
+					new DpiPath("", 2.0m, null, "@2x"),
+				};
+
+			public static DpiPath[] AppIcon
+				=> new[]
+				{
+					new DpiPath("", 1.0m, null, "-16x16", new SKSize(16, 16)),
+					new DpiPath("", 1.0m, null, "-32x32", new SKSize(32, 32)),
+					new DpiPath("", 1.0m, null, "-48x48", new SKSize(48, 48)),
+					new DpiPath("", 1.0m, null, "-128x128", new SKSize(128, 128)),
+					new DpiPath("", 1.0m, null, "-256x256", new SKSize(256, 256)),
+					new DpiPath("", 1.0m, null, "-512x512", new SKSize(512, 512)),
+					new DpiPath("", 1.0m, null, "-1024x1024", new SKSize(1024, 1024)),
+				};
+		}
+
 		public static DpiPath GetOriginal(string platform)
 		{
-			switch (platform.ToLowerInvariant())
+			switch ((platform ?? string.Empty).ToLowerInvariant())
 			{
 				case "ios":
 					return DpiPath.Ios.Original;
@@ -326,14 +351,14 @@ public static DpiPath GetOriginal(string platform)
 					return DpiPath.Wpf.Original;
 				case "tizen":
 					return DpiPath.Tizen.Original;
+				default:
+					return DpiPath.Generic.Original;
 			}
-
-			return null;
 		}
 
 		public static DpiPath[] GetDpis(string platform)
 		{
-			switch (platform.ToLowerInvariant())
+			switch ((platform ?? string.Empty).ToLowerInvariant())
 			{
 				case "ios":
 					return DpiPath.Ios.Image;
@@ -345,16 +370,16 @@ public static DpiPath[] GetDpis(string platform)
 					return DpiPath.Wpf.Image;
 				case "tizen":
 					return DpiPath.Tizen.Image;
+				default:
+					return DpiPath.Generic.Image;
 			}
-
-			return null;
 		}
 
 		public static DpiPath[] GetAppIconDpis(string platform, string appIconName)
 		{
-			DpiPath[] result = null;
+			DpiPath[] result;
 
-			switch (platform.ToLowerInvariant())
+			switch ((platform ?? string.Empty).ToLowerInvariant())
 			{
 				case "ios":
 					result = DpiPath.Ios.AppIcon;
@@ -371,6 +396,9 @@ public static DpiPath[] GetAppIconDpis(string platform, string appIconName)
 				case "tizen":
 					result = DpiPath.Tizen.AppIcon;
 					break;
+				default:
+					result = DpiPath.Generic.AppIcon;
+					break;
 			}
 
 			foreach (var r in result)

src/SingleProject/Resizetizer/src/nuget/buildTransitive/Microsoft.Maui.Resizetizer.After.targets

@@ -113,7 +113,14 @@
 
     <PropertyGroup Condition="'$(_ResizetizerIsAndroidApp)' == 'True' Or '$(_ResizetizerIsiOSApp)' == 'True' Or '$(_ResizetizerIsWPFApp)' == 'True' Or '$(_ResizetizerIsWindowsAppSdk)' == 'True' Or '$(_ResizetizerIsTizenApp)' == 'True'">
         <_ResizetizerIsCompatibleApp>True</_ResizetizerIsCompatibleApp>
+    </PropertyGroup>
+
+    <!-- External backends opt in by setting ResizetizerPlatformType in their targets. -->
+    <PropertyGroup Condition="'$(_ResizetizerIsCompatibleApp)' != 'True' And '$(ResizetizerPlatformType)' != ''">
+        <_ResizetizerIsCompatibleApp>True</_ResizetizerIsCompatibleApp>
+    </PropertyGroup>
 
+    <PropertyGroup Condition="'$(_ResizetizerIsCompatibleApp)' == 'True'">
         <ResizetizeDependsOnTargets>
             $(ResizetizeDependsOnTargets);
             ResizetizeCollectItems;
@@ -254,7 +261,7 @@
 
     <!-- Collect images from referenced projects -->
     <Target Name="ResizetizeCollectItems"
-        Condition="'$(_ResizetizerIsCompatibleApp)' == 'True' And '$(DisableResizetizer)' != 'true'"
+        Condition="'$(DisableResizetizer)' != 'true'"
         BeforeTargets="$(ResizetizeCollectItemsBeforeTargets)"
         AfterTargets="$(ResizetizeCollectItemsAfterTargets)">
 
@@ -375,6 +382,7 @@
             <_MauiAssetItemMetadata Condition="'$(_ResizetizerIsiOSApp)' == 'True'">Link</_MauiAssetItemMetadata>
             <_MauiAssetItemMetadata Condition="'$(_ResizetizerIsWindowsAppSdk)' == 'True'">TargetPath</_MauiAssetItemMetadata>
             <_MauiAssetItemMetadata Condition="'$(_ResizetizerIsTizenApp)' == 'True'">TizenTpkFileName</_MauiAssetItemMetadata>
+            <_MauiAssetItemMetadata Condition="'$(_MauiAssetItemMetadata)' == ''">Link</_MauiAssetItemMetadata>
         </PropertyGroup>
         <GetMauiAssetPath
             ProjectDirectory="$(MSBuildProjectDirectory)"
@@ -395,8 +403,17 @@
         <ItemGroup Condition="'$(_ResizetizerIsTizenApp)' == 'True'">
             <TizenResource Include="@(_MauiAssetItemWithMetadata)" />
         </ItemGroup>
+        <ItemGroup>
+            <MauiProcessedAsset Include="@(_MauiAssetItemWithMetadata)" />
+        </ItemGroup>
     </Target>
 
+    <!-- External backends add packaging targets to ResizetizerAfterAssetProcessingTargets. -->
+    <Target Name="ResizetizerAfterAssetProcessing"
+        AfterTargets="ProcessMauiAssets"
+        DependsOnTargets="$(ResizetizerAfterAssetProcessingTargets)"
+        Condition="'$(EnableMauiAssetProcessing)' == 'true'" />
+
     <Target Name="ProcessMauiSplashScreens"
         Condition="'$(EnableMauiSplashScreenProcessing)' == 'true'"
         Inputs="$(MSBuildThisFileFullPath);$(_ResizetizerTaskAssemblyName);$(_MauiSplashInputsFile);@(MauiSplashScreen)"
@@ -533,6 +550,7 @@
 
         <ItemGroup>
             <_MauiFontCopied Include="$(_MauiIntermediateFonts)*" />
+            <MauiProcessedFont Include="@(MauiFont->'$(_MauiIntermediateFonts)%(Filename)%(Extension)')" />
         </ItemGroup>
 
         <!-- iOS -->
@@ -606,6 +624,12 @@
         </ItemGroup>
     </Target>
 
+    <!-- External backends add packaging targets to ResizetizerAfterFontProcessingTargets. -->
+    <Target Name="ResizetizerAfterFontProcessing"
+        AfterTargets="ProcessMauiFonts"
+        DependsOnTargets="$(ResizetizerAfterFontProcessingTargets)"
+        Condition="'$(EnableMauiFontProcessing)' == 'true'" />
+
     <Target Name="_ReadResizetizeImagesOutputs">
         <ReadLinesFromFile File="$(_ResizetizerOutputsFile)" Condition="Exists ('$(_ResizetizerOutputsFile)')">
             <Output TaskParameter="Lines" ItemName="_ResizetizerOutputs" />
@@ -657,6 +681,38 @@
             Files="@(_ResizetizerImagesToDelete)"
         />
 
+        <ItemGroup>
+            <MauiProcessedImage Include="@(_ResizetizerCollectedImages)" />
+        </ItemGroup>
+
+        <!-- Touch/create our stamp file for outputs -->
+        <Touch Files="$(_ResizetizerStampFile)" AlwaysCreate="True" />
+        <WriteLinesToFile
+            File="$(_ResizetizerOutputsFile)"
+            Lines="@(_ResizetizerCollectedImages->'%(Identity)')"
+            Overwrite="true"
+            WriteOnlyWhenDifferent="true"
+        />
+
+        <!-- Include our images and stamp file as filewrites so they don't get rm'd -->
+        <ItemGroup>
+            <FileWrites Include="@(_ResizetizerCollectedImages)" />
+            <FileWrites Include="$(_ResizetizerStampFile)" />
+            <FileWrites Include="$(_ResizetizerOutputsFile)" />
+        </ItemGroup>
+    </Target>
+
+    <!-- External backends add packaging targets to ResizetizerAfterImageProcessingTargets. -->
+    <Target Name="ResizetizerAfterImageProcessing"
+        AfterTargets="ResizetizeImages"
+        BeforeTargets="_ResizetizeInjectPlatformItems"
+        DependsOnTargets="$(ResizetizerAfterImageProcessingTargets)"
+        Condition="'$(EnableMauiImageProcessing)' == 'true'" />
+
+    <Target Name="_ResizetizeInjectPlatformItems"
+        AfterTargets="ResizetizeImages"
+        Condition="'$(EnableMauiImageProcessing)' == 'true' And ('$(_ResizetizerIsAndroidApp)' == 'True' Or '$(_ResizetizerIsiOSApp)' == 'True' Or '$(_ResizetizerIsWindowsAppSdk)' == 'True' Or '$(_ResizetizerIsWPFApp)' == 'True' Or '$(_ResizetizerIsTizenApp)' == 'True')">
+
         <!-- iOS -->
         <ItemGroup Condition="'$(_ResizetizerIsiOSApp)' == 'True'">
             <!-- Batch the collectd items into BundleResource which iOS expects -->
@@ -729,20 +785,6 @@
             <FileWrites Include="@(_ResizetizerCollectedImages)" />
         </ItemGroup>
 
-        <!-- Touch/create our stamp file for outputs -->
-        <Touch Files="$(_ResizetizerStampFile)" AlwaysCreate="True" />
-        <WriteLinesToFile
-            File="$(_ResizetizerOutputsFile)"
-            Lines="@(_ResizetizerCollectedImages->'%(Identity)')"
-            Overwrite="true"
-            WriteOnlyWhenDifferent="true"
-        />
-
-        <!-- Include our images and stamp file as filewrites so they don't get rm'd -->
-        <ItemGroup>
-            <FileWrites Include="$(_ResizetizerStampFile)" />
-            <FileWrites Include="$(_ResizetizerOutputsFile)" />
-        </ItemGroup>
     </Target>
 
     <!--

src/SingleProject/Resizetizer/test/UnitTests/DpiPathTests.cs

@@ -44,14 +44,56 @@ public void MatchesAnyCase(string platform)
 			}
 
 			[Theory]
-			[InlineData("ANDROID123")]
-			[InlineData("Cars")]
-			[InlineData("123")]
-			public void ReturnsNullOnInvalidPlatform(string platform)
+			[InlineData("macos-appkit")]
+			[InlineData("gtk")]
+			[InlineData("custom-platform")]
+			public void ReturnsFallbackForUnknownPlatform(string platform)
 			{
-				var paths = DpiPath.GetOriginal(platform);
+				var path = DpiPath.GetOriginal(platform);
+
+				Assert.Equal("", path.Path);
+				Assert.Equal(1.0m, path.Scale);
+			}
+		}
+
+		public class GetDpis
+		{
+			[Theory]
+			[InlineData("macos-appkit")]
+			[InlineData("gtk")]
+			[InlineData("custom-platform")]
+			public void ReturnsGenericDesktopFallback(string platform)
+			{
+				var paths = DpiPath.GetDpis(platform);
+
+				Assert.Collection(paths,
+					path => Assert.Equal(1.0m, path.Scale),
+					path =>
+					{
+						Assert.Equal(2.0m, path.Scale);
+						Assert.Equal("@2x", path.ScaleSuffix);
+					});
+			}
+		}
+
+		public class GetAppIconDpis
+		{
+			[Theory]
+			[InlineData("macos-appkit")]
+			[InlineData("gtk")]
+			[InlineData("custom-platform")]
+			public void ReturnsGenericDesktopFallback(string platform)
+			{
+				var paths = DpiPath.GetAppIconDpis(platform, "appicon");
 
-				Assert.Null(paths);
+				Assert.Collection(paths,
+					path => Assert.Equal(16, path.Size!.Value.Width),
+					path => Assert.Equal(32, path.Size!.Value.Width),
+					path => Assert.Equal(48, path.Size!.Value.Width),
+					path => Assert.Equal(128, path.Size!.Value.Width),
+					path => Assert.Equal(256, path.Size!.Value.Width),
+					path => Assert.Equal(512, path.Size!.Value.Width),
+					path => Assert.Equal(1024, path.Size!.Value.Width));
 			}
 		}
 	}

src/SingleProject/Resizetizer/test/UnitTests/ResizetizeImagesTests.cs

@@ -1824,5 +1824,26 @@ public void ShouldResize(string filename, string baseSize, bool resize)
 				Assert.Equal(resize, size.Resize);
 			}
 		}
+
+		public class ExecuteForCustomPlatform : ExecuteForApp
+		{
+			public ExecuteForCustomPlatform(ITestOutputHelper output)
+				: base(output)
+			{
+			}
+
+			[Fact]
+			public void UsesGenericDesktopFallback()
+			{
+				var task = GetNewTask("custom-platform", new TaskItem("images/camera.svg", ResizeMetadata));
+
+				var success = task.Execute();
+
+				Assert.True(success, LogErrorEvents.FirstOrDefault()?.Message);
+				AssertFileSize("camera.png", 1792, 1792);
+				AssertFileSize("camera@2x.png", 3584, 3584);
+				Assert.Equal(2, task.CopiedResources.Length);
+			}
+		}
 	}
 }

src/TestUtils/src/Microsoft.Maui.IntegrationTests/ResizetizerTests.cs

@@ -99,4 +99,43 @@ public void CollectsAssets(string id, string libid, bool unpackaged)
 			Assert.True(File.Exists(Path.Combine(appDir, $"obj\\Debug\\{DotNetCurrent}-windows10.0.19041.0\\win-x64\\resizetizer\\r\\the_image.scale-100.png")),
 				"Windows was missing the image file.");
 	}
+
+	[Fact]
+	public void CustomBackendProcessesImagesWithoutBuiltInOutputInjection()
+	{
+		SetTestIdentifier("custom-backend");
+		var projectDir = TestDirectory;
+		var projectFile = Path.Combine(projectDir, "CustomBackend.csproj");
+		var imageFile = Path.Combine(projectDir, "image.svg");
+
+		File.WriteAllText(imageFile, BlankSvgContents);
+		File.WriteAllText(projectFile,
+			$$"""
+			<Project Sdk="Microsoft.NET.Sdk">
+			  <PropertyGroup>
+			    <TargetFramework>{{DotNetCurrent}}</TargetFramework>
+			    <ResizetizerPlatformType>custom-backend</ResizetizerPlatformType>
+			    <ResizetizerAfterImageProcessingTargets>VerifyCustomBackendImages</ResizetizerAfterImageProcessingTargets>
+			  </PropertyGroup>
+			  <ItemGroup>
+			    <PackageReference Include="Microsoft.Maui.Resizetizer" Version="{{MauiPackageVersion}}" />
+			    <MauiImage Include="image.svg" />
+			  </ItemGroup>
+			  <Target Name="VerifyCustomBackendImages">
+			    <Error Condition="'@(MauiProcessedImage)' == ''" Text="Custom backends must receive processed images." />
+			    <Error Condition="'@(ContentWithTargetPath)' != ''" Text="Custom backends must not receive built-in output injection." />
+			    <WriteLinesToFile File="$(_MauiIntermediateImages)custom-backend.items" Lines="@(MauiProcessedImage)" />
+			  </Target>
+			  <Target Name="VerifyCustomBackendResources" DependsOnTargets="ResizetizeImages" />
+			</Project>
+			""");
+
+		Assert.True(DotnetInternal.Build(projectFile, "Debug", target: "VerifyCustomBackendResources", properties: BuildProps, output: _output),
+			$"Custom backend project failed to process images. Check test output for errors.");
+
+		var outputsFile = Path.Combine(projectDir, "obj", "Debug", DotNetCurrent, "resizetizer", "r", "custom-backend.items");
+		var processedImages = File.ReadAllLines(outputsFile);
+		Assert.Equal(2, processedImages.Length);
+		Assert.All(processedImages, path => Assert.True(File.Exists(path), $"Processed image does not exist: {path}"));
+	}
 }