Fix PDF page dimensions for rendered documents

.github/workflows/build.yml

@@ -15,5 +15,7 @@ jobs:
       - uses: swift-actions/setup-swift@v2
         with:
           swift-version: "6.2"
+      - name: Test
+        run: swift test --configuration release -v
       - name: Build
         run: swift build --configuration release -v

Package.swift

@@ -15,6 +15,10 @@ let package = Package(
         )
     ],
     targets: [
-        .target(name: "PDFViewKit")
+        .target(name: "PDFViewKit"),
+        .testTarget(
+            name: "PDFViewKitTests",
+            dependencies: ["PDFViewKit"]
+        )
     ]
 )

Sources/PDFViewKit/PDFRenderer.swift

@@ -16,11 +16,12 @@ public enum PDFRenderer {
         to destination: URL,
         atPageSize pageSize: some PageSize
     ) throws {
-        let pdfSize = pageSize.size(atDPI: .print)
+        let pdfSize = pageSize.size(atDPI: .pdf)
         let viewRenderingDPI: DPI = .display
         let viewSize = pageSize.size(atDPI: viewRenderingDPI)
 
-        let scaleFactor = pdfSize.width / viewSize.width
+        let viewToPDFScaleFactor = pdfSize.width / viewSize.width
+        let rasterizationScaleFactor = DPI.print.rawValue / viewRenderingDPI.rawValue
         var box = CGRect(
             origin: .zero,
             size: pdfSize
@@ -38,12 +39,12 @@ public enum PDFRenderer {
             let renderer = ImageRenderer(content: renderedView)
             renderer.proposedSize = ProposedViewSize(viewSize)
 
-            renderer.render(rasterizationScale: scaleFactor) { _, renderer in
+            renderer.render(rasterizationScale: rasterizationScaleFactor) { _, renderer in
                 context.beginPDFPage(nil)
 
                 context.scaleBy(
-                    x: scaleFactor,
-                    y: scaleFactor
+                    x: viewToPDFScaleFactor,
+                    y: viewToPDFScaleFactor
                 )
 
                 renderer(context)

Sources/PDFViewKit/PageSizes/DPI.swift

@@ -13,6 +13,8 @@ public enum DPI: CGFloat {
 
     // based on https://www.adobe.com/uk/creativecloud/photography/discover/dots-per-inch-dpi-resolution.html
 
+    case pdf = 72 // PDF user-space points (1/72 inch)
+
     case display = 96
     case displayHigh = 144 // 150%
 

Tests/PDFViewKitTests/PDFRendererTests.swift

@@ -0,0 +1,54 @@
+//
+//  PDFRendererTests.swift
+//  PDFViewKit
+//
+//  Copyright (C) 2026 Sören Gade
+//  See LICENSE for full license.
+//
+
+import Foundation
+import PDFKit
+@testable import PDFViewKit
+import SwiftUI
+import Testing
+
+@MainActor
+struct PDFRendererTests {
+
+    @Test
+    func renderedA4PageUsesPDFPointDimensions() throws {
+        let destination = FileManager.default.temporaryDirectory
+            .appendingPathComponent("PDFViewKit-A4-\(UUID().uuidString).pdf")
+        defer { try? FileManager.default.removeItem(at: destination) }
+
+        let document = PDFViewKit.PDFDocument {
+            Text("Hello, A4")
+        }
+
+        try PDFRenderer.render(
+            document: document,
+            to: destination,
+            atPageSize: DIN.a4
+        )
+
+        let pdfDocument = try #require(PDFDocument(url: destination))
+        let page = try #require(pdfDocument.page(at: 0))
+
+        let mediaBoxSize = page.bounds(for: .mediaBox).size
+
+        #expect(abs(mediaBoxSize.width - a4SizeInPDFPoints.width) < pointTolerance)
+        #expect(abs(mediaBoxSize.height - a4SizeInPDFPoints.height) < pointTolerance)
+    }
+
+    private var a4SizeInPDFPoints: CGSize {
+        CGSize(
+            width: 210 / 25.4 * DPI.pdf.rawValue,
+            height: 297 / 25.4 * DPI.pdf.rawValue
+        )
+    }
+
+    private var pointTolerance: CGFloat {
+        0.001
+    }
+
+}