Render drawings on PDF pages using Swift for iOS

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//
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//  Copyright © 2021-2026 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 PageDrawingExample: Example {
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    override init() {
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        super.init()
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            title = "Draw Overlay Text On All Pages"
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            contentDescription = "Shows how to add custom drawing rendering on pages."
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            category = .miscellaneous
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            priority = 501
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    }
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    override func invoke(with delegate: ExampleRunnerDelegate) -> UIViewController {
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        let document = AssetLoader.document(for: .welcome)
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        document.title = "Draw overlay text on all pages"
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        let pdfController = PDFViewController(document: document)
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        let drawBlock: PDFRenderDrawBlock = { context, _, cropBox, _ in
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            // Careful, this code is executed on background threads. Only use thread-safe drawing methods.
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            // Set up the text and it's drawing attributes.
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            let overlayText = "Example Overlay"
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            let attributes: [NSAttributedString.Key: Any] = [
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                .font: UIFont.boldSystemFont(ofSize: 24.0),
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                .foregroundColor: UIColor.blue
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            ]
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            // Set text drawing mode (fill).
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            context.setTextDrawingMode(.fill)
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            // Calculate the font box to center the text on the page.
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            let boundingBox = overlayText.size(withAttributes: attributes)
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            let point = CGPoint(x: round((cropBox.size.width - boundingBox.width) / 2), y: round((cropBox.size.height - boundingBox.height) / 2))
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            // Finally draw the text.
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            overlayText.draw(at: point, withAttributes: attributes)
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        }
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        document.updateRenderOptions(for: .all) { options in
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            options.drawBlock = drawBlock
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        }
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        return pdfController
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    }
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}