Define abstract PageSize

This allows for easy extensibility of custom page sizes as well as for
defining more standard sizes.

Sources/PDFViewKit/EnvironmentKeys/PDFPageSizeKey.swift

@@ -10,15 +10,15 @@ import SwiftUI
 
 struct PDFPageSizeKey: EnvironmentKey {
 
-    static var defaultValue: DIN = .a4
+    static var defaultValue: PageSize = DIN.a4
 
 }
 
 // MARK: - EnvironmentValues shorthand extension
 
 public extension EnvironmentValues {
 
-    var pdfPageSize: DIN {
+    var pdfPageSize: PageSize {
         get { self[PDFPageSizeKey.self] }
         set { self[PDFPageSizeKey.self] = newValue }
     }
@@ -39,7 +39,7 @@ public extension View {
     ///     - size: The page size for the view and its descendants.
     ///     - force: Whether to apply the size to the view's frame.
     func pdfPageSize(
-        _ size: DIN,
+        _ size: PageSize,
         force: Bool = false
     ) -> some View {
         environment(\.pdfPageSize, size)

Sources/PDFViewKit/Modifiers/ApplyPDFSizeFrameModifier.swift

@@ -10,7 +10,7 @@ import SwiftUI
 
 private struct ApplyPDFSizeFrameModifier: ViewModifier {
 
-    public let size: DIN
+    public let size: PageSize
 
     @Environment(\.pdfRenderingDPI)
     private var pdfRenderingDPI
@@ -32,7 +32,7 @@ extension View {
     /// Applies the given PDF size to the view's frame, taking the current DPI setting into account.
     ///
     /// - Seealso: ``PDFRenderingDPIEnvironmentKey``
-    func applyPDFSizeFrame(size: DIN) -> some View {
+    func applyPDFSizeFrame(size: PageSize) -> some View {
         modifier(ApplyPDFSizeFrameModifier(size: size))
     }
 

Sources/PDFViewKit/PDFDocument.swift

@@ -23,6 +23,15 @@ public struct PDFDocument {
 
 }
 
+// MARK: Default page size for result builders
+
+private extension PDFDocument {
+
+    /// The default size used for pages implicitly created from views.
+    static let defaultPageSize: PageSize = DIN.a4
+
+}
+
 // MARK: - PDFPagesBuilder
 
 @resultBuilder
@@ -42,15 +51,21 @@ public enum PDFPagesBuilder {
     }
 
     public static func buildPartialBlock(first: some View) -> [PDFPage<AnyView>] {
-        [PDFPage(erasing: first)]
+        [PDFPage(
+            size: PDFDocument.defaultPageSize,
+            erasing: first
+        )]
     }
 
     public static func buildPartialBlock(
         accumulated: [PDFPage<AnyView>],
         next: some View
     ) -> [PDFPage<AnyView>] {
         var pages = accumulated
-        pages.append(PDFPage(erasing: next))
+        pages.append(PDFPage(
+            size: PDFDocument.defaultPageSize,
+            erasing: next
+        ))
         return pages
     }
 
@@ -73,15 +88,18 @@ public enum PDFDocumentBuilder {
 
     public static func buildPartialBlock(first: some View) -> PDFDocument {
         PDFDocument {
-            PDFPage {
+            PDFPage(size: PDFDocument.defaultPageSize) {
                 first
             }
         }
     }
 
     public static func buildPartialBlock(accumulated: PDFDocument, next: some View) -> PDFDocument {
         var pages = accumulated.pages
-        pages.append(PDFPage(erasing: next))
+        pages.append(PDFPage(
+            size: PDFDocument.defaultPageSize,
+            erasing: next
+        ))
         return PDFDocument(pages: pages)
     }
 

Sources/PDFViewKit/PDFPage.swift

@@ -14,12 +14,12 @@ import SwiftUI
 /// The alignment of the page's content is top leading.
 public struct PDFPage<Content: View>: View {
 
-    public let size: DIN
+    public let size: PageSize
 
     public let content: Content
 
     public init(
-        size: DIN = .a4,
+        size: PageSize,
         @ViewBuilder _ content: () -> Content
     ) {
         self.size = size
@@ -53,16 +53,21 @@ public extension PDFPage where Content == AnyView {
         }
     }
 
-    init(erasing view: some View) {
-        self.init(erasing: PDFPage({ AnyView(erasing: view) }))
+    init(
+        size: PageSize,
+        erasing view: some View
+    ) {
+        self.init(erasing: PDFPage(size: size) {
+            AnyView(erasing: view)
+        })
     }
 
 }
 
 // MARK: - Previews
 
 #Preview {
-    PDFPage {
+    PDFPage(size: DIN.a4) {
         Text("Hello, World")
     }
 }

Sources/PDFViewKit/PDFRenderer.swift

@@ -13,7 +13,7 @@ public enum PDFRenderer {
     public static func render(
         document: PDFDocument,
         to destination: URL,
-        atPageSize pageSize: DIN
+        atPageSize pageSize: some PageSize
     ) throws {
         let pdfSize = pageSize.size(atDPI: .print)
         let viewRenderingDPI: DPI = .display

Sources/PDFViewKit/DIN.swift → Sources/PDFViewKit/PageSizes/DIN.swift

@@ -8,9 +8,11 @@
 
 import Foundation
 
-// Source: https://de.wikipedia.org/wiki/Papierformat#Internationale_Papierformate_(ISO/DIN)
+/// Defines standard page sizes in the german DIN system.
 public enum DIN {
 
+    // Source: https://de.wikipedia.org/wiki/Papierformat#Internationale_Papierformate_(ISO/DIN)
+
     case a0
     case a1
     case a2
@@ -25,11 +27,11 @@ public enum DIN {
 
 }
 
-// MARK: Physical page sizes
+// MARK: PageSize
 
-public extension DIN {
+extension DIN: PageSize {
 
-    var width: Measurement<UnitLength> {
+    public var width: Measurement<UnitLength> {
         switch self {
         case .a0:
             Measurement(
@@ -99,7 +101,7 @@ public extension DIN {
         }
     }
 
-    var height: Measurement<UnitLength> {
+    public var height: Measurement<UnitLength> {
         switch self {
         case .a0:
             Measurement(
@@ -169,20 +171,3 @@ public extension DIN {
     }
 
 }
-
-// MARK: Calculated properties based on physical sizes
-
-public extension DIN {
-
-    var aspectRatio: CGFloat {
-        width.converted(to: .millimeters).value / height.converted(to: .millimeters).value
-    }
-
-    func size(atDPI dpi: DPI) -> CGSize {
-        CGSize(
-            width: width.converted(to: .inches).value * dpi.rawValue,
-            height: height.converted(to: .inches).value * dpi.rawValue
-        )
-    }
-
-}

Sources/PDFViewKit/DPI.swift → Sources/PDFViewKit/PageSizes/DPI.swift

@@ -8,9 +8,11 @@
 
 import Foundation
 
+/// Defines specific dots per inch resolutions.
 public enum DPI: CGFloat {
 
     // based on https://www.adobe.com/uk/creativecloud/photography/discover/dots-per-inch-dpi-resolution.html
+
     case display = 96
     case displayHigh = 144 // 150%
 

Sources/PDFViewKit/PageSizes/PageSize.swift

@@ -0,0 +1,46 @@
+//
+//  PageSize.swift
+//  PDFViewKit
+//
+//  Copyright (C) 2024 Sören Gade
+//  See LICENSE for full license.
+//
+
+import Foundation
+
+/// A type that defines page sizes.
+public protocol PageSize {
+
+    /// The page's physical width.
+    var width: Measurement<UnitLength> { get }
+
+    /// The page's physical height.
+    var height: Measurement<UnitLength> { get }
+
+    /// The page's size aspect ratio.
+    var aspectRatio: CGFloat { get }
+
+    /// Calculates the page's dot size at the given ``DPI`` rendering scale.
+    ///
+    /// - Parameters:
+    ///     - dpi: The page resolution of dots per inch.
+    func size(atDPI dpi: DPI) -> CGSize
+
+}
+
+// MARK: Default implementation
+
+public extension PageSize {
+
+    var aspectRatio: CGFloat {
+        width.converted(to: .millimeters).value / height.converted(to: .millimeters).value
+    }
+
+    func size(atDPI dpi: DPI) -> CGSize {
+        CGSize(
+            width: width.converted(to: .inches).value * dpi.rawValue,
+            height: height.converted(to: .inches).value * dpi.rawValue
+        )
+    }
+
+}