Implement View.italic and Font.italic modifiers

Sources/AppKitBackend/AppKitBackend.swift

@@ -633,8 +633,11 @@ public final class AppKitBackend: AppBackend {
         onChange: @escaping (Bool) -> Void
     ) {
         let toggle = toggle as! NSButton
+        toggle.attributedTitle = Self.attributedString(
+            for: label,
+            in: environment.with(\.multilineTextAlignment, .center)
+        )
         toggle.isEnabled = environment.isEnabled
-        toggle.title = label
         toggle.onAction = { toggle in
             let toggle = toggle as! NSButton
             onChange(toggle.state == .on)
@@ -1131,15 +1134,23 @@ public final class AppKitBackend: AppBackend {
     private static func font(for font: Font.Resolved) -> NSFont {
         let size = CGFloat(font.pointSize)
         let weight = weight(for: font.weight)
+
+        let nsFont: NSFont
         switch font.identifier.kind {
             case .system:
                 switch font.design {
                     case .default:
-                        return NSFont.systemFont(ofSize: size, weight: weight)
+                        nsFont = NSFont.systemFont(ofSize: size, weight: weight)
                     case .monospaced:
-                        return NSFont.monospacedSystemFont(ofSize: size, weight: weight)
+                        nsFont = NSFont.monospacedSystemFont(ofSize: size, weight: weight)
                 }
         }
+
+        if font.isItalic {
+            return NSFontManager.shared.convert(nsFont, toHaveTrait: .italicFontMask)
+        } else {
+            return nsFont
+        }
     }
 
     private static func weight(for weight: Font.Weight) -> NSFont.Weight {

Sources/Gtk/Utility/CSS/CSSProperty.swift

@@ -70,6 +70,10 @@ public struct CSSProperty: Equatable {
         CSSProperty(key: "font-family", value: family)
     }
 
+    public static func fontStyle(_ style: String) -> CSSProperty {
+        CSSProperty(key: "font-style", value: style)
+    }
+
     public static func rgba(_ color: Color) -> String {
         let red = color.red * 255
         let green = color.green * 255

Sources/Gtk3/Utility/CSS/CSSProperty.swift

@@ -70,6 +70,10 @@ public struct CSSProperty: Equatable {
         CSSProperty(key: "font-family", value: family)
     }
 
+    public static func fontStyle(_ style: String) -> CSSProperty {
+        CSSProperty(key: "font-style", value: style)
+    }
+
     public static func rgba(_ color: Color) -> String {
         let red = color.red * 255
         let green = color.green * 255

Sources/Gtk3Backend/Gtk3Backend.swift

@@ -799,6 +799,10 @@ public final class Gtk3Backend: AppBackend {
         toggle.toggled = { widget in
             onChange(widget.active)
         }
+        toggle.css.clear()
+        // This is a control, but we set isControl to false anyway because isControl overrides
+        // the button background and makes the on and off states of the toggle look identical.
+        toggle.css.set(properties: Self.cssProperties(for: environment, isControl: false))
     }
 
     public func setState(ofToggle toggle: Widget, to state: Bool) {
@@ -1474,6 +1478,10 @@ public final class Gtk3Backend: AppBackend {
                 }
         }
 
+        if font.isItalic {
+            properties.append(.fontStyle("italic"))
+        }
+
         if isControl {
             switch environment.colorScheme {
                 case .light:

Sources/GtkBackend/GtkBackend.swift

@@ -775,6 +775,10 @@ public final class GtkBackend: AppBackend {
         toggle.toggled = { widget in
             onChange(widget.active)
         }
+        toggle.css.clear()
+        // This is a control, but we set isControl to false anyway because isControl overrides
+        // the button background and makes the on and off states of the toggle look identical.
+        toggle.css.set(properties: Self.cssProperties(for: environment, isControl: false))
     }
 
     public func setState(ofToggle toggle: Widget, to state: Bool) {
@@ -1525,6 +1529,10 @@ public final class GtkBackend: AppBackend {
                 }
         }
 
+        if font.isItalic {
+            properties.append(.fontStyle("italic"))
+        }
+
         if isControl {
             switch environment.colorScheme {
                 case .light:

Sources/SwiftCrossUI/Values/Font.swift

@@ -56,6 +56,13 @@ public struct Font: Hashable, Sendable {
         return font
     }
 
+    /// Selects whether or not to italicize the font.
+    public func italic(_ italic: Bool = true) -> Font {
+        var font = self
+        font.overlay.italicize = italic
+        return font
+    }
+
     /// Overrides the font's weight. Takes an optional for convenience. Does
     /// nothing if given `nil`.
     public func weight(_ weight: Weight?) -> Font {
@@ -167,6 +174,10 @@ public struct Font: Hashable, Sendable {
         /// overlay has been applied if one is present.
         var emphasize: Bool = false
 
+        /// If `true`, overrides the font to be italicized. If `false`, does
+        /// nothing.
+        var italicize: Bool = false
+
         /// Overrides the font's design.
         var design: Design?
 
@@ -185,6 +196,9 @@ public struct Font: Hashable, Sendable {
             if emphasize {
                 resolvedFont.weight = emphasizedWeight
             }
+            if italicize {
+                resolvedFont.isItalic = true
+            }
             if let pointSize {
                 resolvedFont.pointSize = pointSize
             }
@@ -212,6 +226,7 @@ public struct Font: Hashable, Sendable {
         public var lineHeight: Double
         public var weight: Weight
         public var design: Design
+        public var isItalic: Bool
     }
 
     public struct Context: Sendable {
@@ -237,7 +252,8 @@ public struct Font: Hashable, Sendable {
                             //   constant ratio).
                             lineHeight: (size * 1.25).rounded(.awayFromZero),
                             weight: weight ?? .regular,
-                            design: design ?? .default
+                            design: design ?? .default,
+                            isItalic: false
                         )
                 }
             case .dynamic(let textStyle):
@@ -248,7 +264,8 @@ public struct Font: Hashable, Sendable {
                     pointSize: resolvedTextStyle.pointSize,
                     lineHeight: resolvedTextStyle.lineHeight,
                     weight: resolvedTextStyle.weight,
-                    design: .default
+                    design: .default,
+                    isItalic: false
                 )
         }
 

Sources/SwiftCrossUI/Views/Modifiers/Style/FontModifier.swift

@@ -29,7 +29,7 @@
     /// a ``Font/TextStyle``, forces the style's emphasized weight to be
     /// used.
     ///
     /// Deprecated and renamed for clarity. Use ``View.fontWeight(_:)``
     /// to make text bold.
     @available(
         *, deprecated,
@@ -52,4 +52,14 @@
             )
         }
     }
+
+    /// Forces any contained text to become italic.
+    public func italic() -> some View {
+        EnvironmentModifier(self) { environment in
+            return environment.with(
+                \.fontOverlay.italicize,
+                true
+            )
+        }
+    }
 }

Sources/UIKitBackend/Font+UIFont.swift

@@ -3,6 +3,7 @@ import UIKit
 
 extension Font.Resolved {
     var uiFont: UIFont {
+        let uiFont: UIFont
         switch identifier.kind {
             case .system:
                 let weight: UIFont.Weight =
@@ -29,10 +30,20 @@ extension Font.Resolved {
 
                 switch design {
                     case .monospaced:
-                        return .monospacedSystemFont(ofSize: CGFloat(pointSize), weight: weight)
+                        uiFont = .monospacedSystemFont(ofSize: CGFloat(pointSize), weight: weight)
                     case .default:
-                        return .systemFont(ofSize: CGFloat(pointSize), weight: weight)
+                        uiFont = .systemFont(ofSize: CGFloat(pointSize), weight: weight)
                 }
         }
+
+        if isItalic {
+            let descriptor = uiFont.fontDescriptor.withSymbolicTraits(.traitItalic)
+            return UIFont(
+                descriptor: descriptor ?? uiFont.fontDescriptor,
+                size: CGFloat(pointSize)
+            )
+        } else {
+            return uiFont
+        }
     }
 }

Sources/WinUIBackend/WinUIBackend.swift

@@ -1752,6 +1752,9 @@ extension EnvironmentValues {
         control.fontWeight.weight = resolvedFont.winUIFontWeight
         control.foreground = winUIForegroundBrush
         control.isEnabled = isEnabled
+        if resolvedFont.isItalic {
+            control.fontStyle = .italic
+        }
         switch colorScheme {
             case .light:
                 control.requestedTheme = .light
@@ -1766,6 +1769,9 @@ extension EnvironmentValues {
         textBlock.fontSize = resolvedFont.pointSize
         textBlock.fontWeight.weight = resolvedFont.winUIFontWeight
         textBlock.foreground = winUIForegroundBrush
+        if resolvedFont.isItalic {
+            textBlock.fontStyle = .italic
+        }
     }
 }