Add Upscaling CIFilter + CIImageProcessorKernel

Package.swift

@@ -23,6 +23,10 @@ let package = Package(
             ]
         ),
         .target(name: "Upscaling"),
-        .testTarget(name: "UpscalingTests", dependencies: ["Upscaling"], resources: [.process("Resources")])
+        .testTarget(
+            name: "UpscalingTests",
+            dependencies: ["Upscaling"],
+            resources: [.process("Resources")]
+        )
     ]
 )

Sources/Upscaling/CoreImage/UpscalingFilter.swift

@@ -0,0 +1,48 @@
+import CoreImage
+import Foundation
+#if canImport(MetalFX)
+import MetalFX
+#endif
+
+// MARK: - UpscalingFilter
+
+public class UpscalingFilter: CIFilter {
+    // MARK: Public
+
+    public var inputImage: CIImage?
+    public var outputSize: CGSize?
+
+    override public var outputImage: CIImage? {
+        #if canImport(MetalFX)
+        guard let device, let inputImage, let outputSize else { return nil }
+
+        if spatialScaler?.inputSize != inputImage.extent.size || spatialScaler?.outputSize != outputSize {
+            let spatialScalerDescriptor = MTLFXSpatialScalerDescriptor()
+            spatialScalerDescriptor.inputSize = inputImage.extent.size
+            spatialScalerDescriptor.outputSize = outputSize
+            spatialScalerDescriptor.colorTextureFormat = .bgra8Unorm
+            spatialScalerDescriptor.outputTextureFormat = .bgra8Unorm
+            spatialScalerDescriptor.colorProcessingMode = .perceptual
+            spatialScaler = spatialScalerDescriptor.makeSpatialScaler(device: device)
+        }
+
+        guard let spatialScaler else { return nil }
+
+        return try? UpscalingImageProcessorKernel.apply(
+            withExtent: CGRect(origin: .zero, size: spatialScaler.outputSize),
+            inputs: [inputImage],
+            arguments: ["spatialScaler": spatialScaler]
+        )
+        #else
+        return inputImage
+        #endif
+    }
+
+    // MARK: Private
+
+    private let device = MTLCreateSystemDefaultDevice()
+
+    #if canImport(MetalFX)
+    private var spatialScaler: MTLFXSpatialScaler?
+    #endif
+}

Sources/Upscaling/CoreImage/UpscalingImageProcessorKernel.swift

@@ -0,0 +1,47 @@
+import CoreImage
+import Foundation
+#if canImport(MetalFX)
+import MetalFX
+#endif
+
+// MARK: - UpscalingImageProcessorKernel
+
+public class UpscalingImageProcessorKernel: CIImageProcessorKernel {
+    override public class var synchronizeInputs: Bool { false }
+    override public class var outputFormat: CIFormat { .BGRA8 }
+
+    override public class func formatForInput(at _: Int32) -> CIFormat { .BGRA8 }
+
+    override public class func process(
+        with inputs: [any CIImageProcessorInput]?,
+        arguments: [String: Any]?,
+        output: any CIImageProcessorOutput
+    ) throws {
+        #if canImport(MetalFX)
+        guard let spatialScaler = arguments?["spatialScaler"] as? MTLFXSpatialScaler,
+              let inputTexture = inputs?.first?.metalTexture,
+              let outputTexture = output.metalTexture,
+              let commandBuffer = output.metalCommandBuffer else {
+            return
+        }
+        spatialScaler.colorTexture = inputTexture
+        spatialScaler.outputTexture = outputTexture
+        spatialScaler.encode(commandBuffer: commandBuffer)
+        #endif
+    }
+
+    override public class func roi(
+        forInput _: Int32,
+        arguments: [String: Any]?,
+        outputRect: CGRect
+    ) -> CGRect {
+        #if canImport(MetalFX)
+        guard let spatialScaler = arguments?["spatialScaler"] as? MTLFXSpatialScaler else {
+            return .null
+        }
+        return CGRect(origin: .zero, size: spatialScaler.inputSize)
+        #else
+        return outputRect
+        #endif
+    }
+}

Sources/Upscaling/Extensions/MTLFXSpatialScaler+Extensions.swift

@@ -0,0 +1,13 @@
+#if canImport(MetalFX)
+import MetalFX
+
+extension MTLFXSpatialScaler {
+    var inputSize: CGSize {
+        CGSize(width: inputWidth, height: inputHeight)
+    }
+
+    var outputSize: CGSize {
+        CGSize(width: outputWidth, height: outputHeight)
+    }
+}
+#endif

Tests/UpscalingTests/UpscalingTests.swift

@@ -1,3 +1,5 @@
+import CoreImage
+import MetalFX
 @testable import Upscaling
 import XCTest
 
@@ -42,4 +44,21 @@ final class UpscalingTests: XCTestCase {
         // ensure progress works
         throw XCTSkip("unimplemented")
     }
+
+    func testFilter() async throws {
+        let inputImage = CIImage(
+            contentsOf: Bundle.module.url(forResource: "ladybird", withExtension: "jpg")!
+        )!
+        let outputSize = CGSize(
+            width: inputImage.extent.width * 8,
+            height: inputImage.extent.height * 8
+        )
+
+        let filter = UpscalingFilter()
+        filter.inputImage = inputImage
+        filter.outputSize = outputSize
+        let outputImage = filter.outputImage!
+        // TODO: - diff images
+        XCTAssertEqual(outputImage.extent.size, outputSize)
+    }
 }