Create a custom appearance stream generator in Swift for iOS

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//
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//  Copyright © 2019-2025 PSPDFKit GmbH. All rights reserved.
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//
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//  The Nutrient sample applications are licensed with a modified BSD license.
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//  Please see License for details. This notice may not be removed from this file.
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//
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import PSPDFKit
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import PSPDFKitUI
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class AppearanceStreamGeneratorWithCustomDrawingExample: Example {
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    override init() {
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        super.init()
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        title = "Appearance Stream Generator with a custom drawing block"
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        contentDescription = "Shows how to add additional custom drawing for a vector stamp annotation."
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        category = .annotations
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        priority = 70
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    }
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    override func invoke(with delegate: ExampleRunnerDelegate) -> UIViewController {
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        let document = AssetLoader.document(for: .annualReport)
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        document.annotationSaveMode = .disabled
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        let logoURL = AssetLoader.assetURL(for: "PSPDFKit Logo.pdf")
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        let pageIndex: PageIndex = 0
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        // Add a stamp annotation.
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        let stampAnnotation = StampAnnotation()
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        stampAnnotation.boundingBox = CGRect(x: 180.0, y: 150.0, width: 444.0, height: 500.0)
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        stampAnnotation.color = UIColor(red: 0, green: 100 / 255, blue: 0, alpha: 1)
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        stampAnnotation.fillColor = UIColor.clear
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        stampAnnotation.alpha = 0.5
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        stampAnnotation.lineWidth = 5
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        stampAnnotation.pageIndex = pageIndex
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        // Create the appearance stream generator and setup its drawing block.
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        let appearanceStreamGenerator = FileAppearanceStreamGenerator(fileURL: logoURL)
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        appearanceStreamGenerator.drawingBlock = { context in
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            // Custom drawing: Draw a green square border around the stamp.
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            let box = stampAnnotation.boundingBox
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            let color = stampAnnotation.color
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            context.saveGState()
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            guard let colorRef = color?.cgColor else {
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                return
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            }
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            context.setStrokeColor(colorRef)
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            context.stroke(box)
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            context.setFillColor(colorRef)
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            let lineWidth = stampAnnotation.lineWidth
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            let strokeRect: CGRect = box.insetBy(dx: lineWidth / 2.0, dy: lineWidth / 2.0)
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            let path = CGPath(rect: strokeRect, transform: nil)
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            context.setLineWidth(lineWidth)
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            context.setAlpha(stampAnnotation.alpha)
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            context.addPath(path)
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            context.drawPath(using: .stroke)
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            context.restoreGState()
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        }
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        // Set the annotation's appearance stream generator.
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        stampAnnotation.appearanceStreamGenerator = appearanceStreamGenerator
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        document.add(annotations: [stampAnnotation])
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        let controller = PDFViewController(document: document)
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        return controller
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    }
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}