PDF page scale and resize using Swift for iOS

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//
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//  Copyright © 2016-2026 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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/// Shows how to scale pages with `PSPDFProcessor`.
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final class PageScalingExample: Example {
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    // MARK: Lifecycle
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    override init() {
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        super.init()
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        contentDescription = "Shows how to scale pages with PSPDFProcessor"
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        category = .documentProcessing
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        priority = 13
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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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        return PageScalingPDFViewController(document: document)
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    }
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}
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/// Scales pages of it's document.
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private final class PageScalingPDFViewController: PDFViewController {
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    // MARK: Lifecycle
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    override func commonInit(with document: Document?, configuration: PDFConfiguration) {
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        super.commonInit(with: document, configuration: configuration)
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        let actions = [("Page Size", #selector(showPageSize)), ("Scale", #selector(scale))]
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        let barButtonItems = actions.map { title, selector in
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            UIBarButtonItem(title: title, style: .plain, target: self, action: selector)
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        }
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        navigationItem.setRightBarButtonItems(barButtonItems.reversed(), for: .document, animated: false)
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    }
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    // MARK: Bar Button Item Actions
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    /// Scales all pages of the current document.
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    ///
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    /// - Parameter sender: Action sender.
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    @objc
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    private func scale(_ sender: UIBarButtonItem) {
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        guard let document else {
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            print("Processor configuration needs a valid document")
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            return
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        }
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        guard let configuration = Processor.Configuration(document: document) else { return }
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        // We want to scale down every page to half it's size.
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        let newPageSizes: [(PageIndex, CGSize)] = pageSizes!.map { ($0.0, CGSize(width: $0.1!.width / 2, height: $0.1!.height / 2)) }
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        for (page, pageSize) in newPageSizes {
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            configuration.scalePage(page, to: pageSize)
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        }
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        let scaledDocumentURL = FileHelper.temporaryPDFFileURL(prefix: "scaled")
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        do {
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            // Process annotations.
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            // `PSPDFProcessor` doesn't modify the document, but creates an output file instead.
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            let processor = Processor(configuration: configuration, securityOptions: nil)
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            processor.delegate = self
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            try processor.write(toFileURL: scaledDocumentURL)
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        } catch {
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            print("Error while processing document: \(error)")
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            return
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        }
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        presentProcessedDocument(scaledDocumentURL)
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    }
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    /// Shows the current page size as an alert.
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    ///
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    /// - Parameter sender: Action sender.
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    @objc
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    private func showPageSize(_ sender: UIBarButtonItem) {
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        let pageSize = pageSizeForPage(at: pageIndex)!
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        let message = "Height: \(pageSize.height)\nWidth: \(pageSize.width)"
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        let alertController = UIAlertController(title: "Page Size", message: message, preferredStyle: .alert)
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        let alertAction = UIAlertAction(title: "Dismiss", style: .default)
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        alertController.addAction(alertAction)
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        present(alertController, animated: true, completion: nil)
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    }
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    // MARK: Helper
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    /// Page sizes of the document.
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    ///
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    /// - Returns: Array of tuples (page number, page size)
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    private var pageSizes: [(PageIndex, CGSize?)]? {
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        guard let document else { return nil }
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        return (0..<document.pageCount).flatMap { [($0, self.pageSizeForPage(at: $0))] }
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    }
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    /// Gets a page's size.
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    ///
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    /// - Parameter page: Page to get size from.
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    /// - Returns: Page size.
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    private func pageSizeForPage(at index: PageIndex) -> CGSize? {
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        let pageInfo = document?.pageInfoForPage(at: index)
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        return pageInfo?.size
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    }
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    /// Presents a processed document.
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    ///
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    /// - Parameter processedDocumentURL: `URL` of processed document.
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    private func presentProcessedDocument(_ processedDocumentURL: URL) {
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        let processedDocument = Document(url: processedDocumentURL)
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        let pdfController = PageScalingPDFViewController(document: processedDocument)
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        let rightBarButtonItems = Array(pdfController.navigationItem.rightBarButtonItems(for: .document)!.dropFirst())
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        pdfController.navigationItem.setRightBarButtonItems(rightBarButtonItems, for: .document, animated: false)
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        let navigationController = UINavigationController(rootViewController: pdfController)
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        present(navigationController, animated: true, completion: nil)
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    }
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}
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extension PageScalingPDFViewController: ProcessorDelegate {
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    nonisolated func processor(_ processor: Processor, didProcessPage currentPage: UInt, totalPages: UInt) {
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        print("Progress: \(currentPage + 1) of \(totalPages)")
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    }
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}