Add overlay modifier

Author: colemancda

AndroidSwiftUICore/Sources/AndroidSwiftUICore/Primitives/Overlay.swift

@@ -0,0 +1,41 @@
+//
+//  Overlay.swift
+//  AndroidSwiftUICore
+//
+//  `.overlay { … }` layers content over a view, sized to the base. Emitted as an
+//  Overlay node whose first child is the base and second is the overlay; the
+//  interpreter stacks the overlay at the base's size with the given alignment.
+//
+
+public struct _OverlayView<Base: View, Overlay: View>: View {
+    internal let base: Base
+    internal let overlay: Overlay
+    internal let alignment: Alignment
+    public typealias Body = Never
+}
+
+extension _OverlayView: PrimitiveView {
+    public func _render(in context: ResolveContext) -> RenderNode {
+        RenderNode(
+            type: "Overlay",
+            id: context.path,
+            props: [
+                "horizontal": .string(alignment.horizontal.rawValue),
+                "vertical": .string(alignment.vertical.rawValue),
+            ],
+            children: [
+                Evaluator.resolve(base, context.descending("base")),
+                Evaluator.resolve(overlay, context.descending("overlay")),
+            ]
+        )
+    }
+}
+
+public extension View {
+    func overlay<V: View>(
+        alignment: Alignment = .center,
+        @ViewBuilder content: () -> V
+    ) -> _OverlayView<Self, V> {
+        _OverlayView(base: self, overlay: content(), alignment: alignment)
+    }
+}