Implement View.overlay(content:) modifier

Author: stackotter

Sources/SwiftCrossUI/Modifiers/OverlayModifier.swift

@@ -0,0 +1,91 @@
+extension View {
+    public func overlay(@ViewBuilder content: () -> some View) -> some View {
+        OverlayModifier(content: self, overlay: content())
+    }
+}
+
+struct OverlayModifier<Content: View, Overlay: View>: TypeSafeView {
+    typealias Children = TupleView2<Content, Overlay>.Children
+
+    var body: TupleView2<Content, Overlay>
+
+    init(content: Content, overlay: Overlay) {
+        body = TupleView2(content, overlay)
+    }
+
+    func children<Backend: AppBackend>(
+        backend: Backend,
+        snapshots: [ViewGraphSnapshotter.NodeSnapshot]?,
+        environment: EnvironmentValues
+    ) -> TupleView2<Content, Overlay>.Children {
+        body.children(
+            backend: backend,
+            snapshots: snapshots,
+            environment: environment
+        )
+    }
+
+    func layoutableChildren<Backend: AppBackend>(
+        backend: Backend,
+        children: TupleView2<Content, Overlay>.Children
+    ) -> [LayoutSystem.LayoutableChild] {
+        []
+    }
+
+    func asWidget<Backend: AppBackend>(
+        _ children: TupleView2<Content, Overlay>.Children, backend: Backend
+    ) -> Backend.Widget {
+        body.asWidget(children, backend: backend)
+    }
+
+    func update<Backend: AppBackend>(
+        _ widget: Backend.Widget,
+        children: TupleView2<Content, Overlay>.Children,
+        proposedSize: SIMD2<Int>,
+        environment: EnvironmentValues,
+        backend: Backend,
+        dryRun: Bool
+    ) -> ViewUpdateResult {
+        let contentResult = children.child0.update(
+            with: body.view0,
+            proposedSize: proposedSize,
+            environment: environment,
+            dryRun: dryRun
+        )
+        let contentSize = contentResult.size
+        let overlayResult = children.child1.update(
+            with: body.view1,
+            proposedSize: contentSize.size,
+            environment: environment,
+            dryRun: dryRun
+        )
+        let overlaySize = overlayResult.size
+
+        let frameSize = SIMD2(
+            max(contentSize.size.x, overlaySize.size.x),
+            max(contentSize.size.y, overlaySize.size.y)
+        )
+
+        if !dryRun {
+            let contentPosition = (frameSize &- contentSize.size) / 2
+            let overlayPosition = (frameSize &- overlaySize.size) / 2
+
+            backend.setPosition(ofChildAt: 0, in: widget, to: contentPosition)
+            backend.setPosition(ofChildAt: 1, in: widget, to: overlayPosition)
+
+            backend.setSize(of: widget, to: frameSize)
+        }
+
+        return ViewUpdateResult(
+            size: ViewSize(
+                size: frameSize,
+                idealSize: contentSize.idealSize,
+                minimumWidth: max(contentSize.minimumWidth, overlaySize.minimumWidth),
+                minimumHeight: max(contentSize.minimumHeight, overlaySize.minimumHeight),
+                maximumWidth: min(contentSize.maximumWidth, overlaySize.maximumWidth),
+                maximumHeight: min(contentSize.maximumHeight, overlaySize.maximumHeight)
+            ),
+            childResults: [contentResult, overlayResult]
+        )
+    }
+}