Implement multilineTextAlignment modifier (for GtkBackend and AppKitBackend)

Author: stackotter

Sources/AppKitBackend/AppKitBackend.swift

@@ -303,11 +303,10 @@ public final class AppKitBackend: AppBackend {
             width: (proposedFrame?.x).map(CGFloat.init) ?? 0,
             height: .greatestFiniteMagnitude
         )
-        let font = Self.font(for: environment)
         let rect = NSString(string: text).boundingRect(
             with: proposedSize,
             options: [.usesLineFragmentOrigin],
-            attributes: [.font: font]
+            attributes: Self.attributes(forTextIn: environment)
         )
         return SIMD2(
             Int(rect.size.width.rounded(.awayFromZero)),
@@ -644,13 +643,30 @@ public final class AppKitBackend: AppBackend {
     ) -> NSAttributedString {
         NSAttributedString(
             string: text,
-            attributes: [
-                .foregroundColor: environment.foregroundColor.nsColor,
-                .font: font(for: environment),
-            ]
+            attributes: attributes(forTextIn: environment)
         )
     }
 
+    private static func attributes(
+        forTextIn environment: Environment
+    ) -> [NSAttributedString.Key: Any] {
+        let paragraphStyle = NSMutableParagraphStyle()
+        paragraphStyle.alignment =
+            switch environment.multilineTextAlignment {
+                case .leading:
+                    .left
+                case .center:
+                    .center
+                case .trailing:
+                    .right
+            }
+        return [
+            .foregroundColor: environment.foregroundColor.nsColor,
+            .font: font(for: environment),
+            .paragraphStyle: paragraphStyle,
+        ]
+    }
+
     private static func font(for environment: Environment) -> NSFont {
         switch environment.font {
             case .system(let size, let weight, let design):

Sources/GtkBackend/GtkBackend.swift

@@ -278,6 +278,15 @@ public final class GtkBackend: AppBackend {
         textView.label = content
         textView.wrap = true
         textView.lineWrapMode = .wordCharacter
+        textView.justify =
+            switch environment.multilineTextAlignment {
+                case .leading:
+                    Justification.left
+                case .center:
+                    Justification.center
+                case .trailing:
+                    Justification.right
+            }
 
         textView.css.clear()
         textView.css.set(properties: Self.cssProperties(for: environment))

Sources/SwiftCrossUI/Modifiers/MultilineTextAlignment.swift

@@ -0,0 +1,9 @@
+extension View {
+    /// Sets the alignment of lines of text relative to each other in multiline
+    /// text views.
+    public func multilineTextAlignment(_ alignment: HorizontalAlignment) -> some View {
+        return EnvironmentModifier(self) { environment in
+            return environment.with(\.multilineTextAlignment, alignment)
+        }
+    }
+}

Sources/SwiftCrossUI/ViewGraph/Environment.swift

@@ -5,6 +5,7 @@ public struct Environment {
     public var layoutSpacing: Int
     public var foregroundColor: Color
     public var font: Font
+    public var multilineTextAlignment: HorizontalAlignment
 
     init() {
         onResize = { _ in }
@@ -13,6 +14,7 @@ public struct Environment {
         layoutSpacing = 10
         foregroundColor = .black
         font = .system(size: 12)
+        multilineTextAlignment = .leading
     }
 
     public func with<T>(_ keyPath: WritableKeyPath<Self, T>, _ newValue: T) -> Self {