Create experimental LVGL backend (enough to run the counter example without padding)

Author: stackotter

Examples/Counter/CounterApp.swift

@@ -1,14 +1,11 @@
-import QtBackend
 import SwiftCrossUI
 
-// #if canImport(GtkBackend)
-//     import GtkBackend
-//     typealias SelectedBackend = GtkBackend
-// #else
-//     #error("No valid backends found")
-// #endif
-
-typealias SelectedBackend = QtBackend
+#if canImport(GtkBackend)
+    import GtkBackend
+    typealias SelectedBackend = GtkBackend
+#else
+    #error("No valid backends found")
+#endif
 
 class CounterState: Observable {
     @Observed

Package.resolved

@@ -12,10 +12,6 @@ var dependencies: [Package.Dependency] = [
         url: "https://github.com/apple/swift-syntax.git",
         from: "508.0.0"
     ),
-    .package(
-        url: "https://github.com/Longhanks/qlift",
-        revision: "ddab1f1ecc113ad4f8e05d2999c2734cdf706210"
-    ),
 ]
 
 #if swift(>=5.6) && !os(Windows)
@@ -116,6 +112,33 @@ if checkQtInstalled() {
     )
     backendTargets.append("QtBackend")
     exampleDependencies.append("QtBackend")
+    dependencies.append(
+        .package(
+            url: "https://github.com/Longhanks/qlift",
+            revision: "ddab1f1ecc113ad4f8e05d2999c2734cdf706210"
+        )
+    )
+}
+
+if checkSDL2Installed() {
+    conditionalTargets.append(
+        .target(
+            name: "LVGLBackend",
+            dependencies: [
+                "SwiftCrossUI",
+                .product(name: "LVGL", package: "LVGLSwift"),
+                .product(name: "CLVGL", package: "LVGLSwift"),
+            ]
+        )
+    )
+    backendTargets.append("LVGLBackend")
+    exampleDependencies.append("LVGLBackend")
+    dependencies.append(
+        .package(
+            url: "https://github.com/PADL/LVGLSwift",
+            revision: "fb696362c92a60a2793202a88053fbff298bbd7f"
+        )
+    )
 }
 
 let package = Package(
@@ -214,6 +237,25 @@ func checkQtInstalled() -> Bool {
     #endif
 }
 
+func checkSDL2Installed() -> Bool {
+    #if os(Windows)
+        // TODO: Test SDL backend on Windows
+        return false
+    #else
+        let process = Process()
+        process.executableURL = URL(fileURLWithPath: "/bin/bash")
+        process.arguments = ["-c", "sdl2-config --version"]
+        process.standardOutput = Pipe()
+        do {
+            try process.run()
+            process.waitUntilExit()
+            return true
+        } catch {
+            return false
+        }
+    #endif
+}
+
 func getGtk4MinorVersion() -> Int? {
     #if os(Windows)
         guard let pkgConfigPath = ProcessInfo.processInfo.environment["PKG_CONFIG_PATH"],

Package.swift

@@ -0,0 +1,180 @@
+import CLVGL
+import Foundation
+import LVGL
+import SwiftCrossUI
+
+public struct LVGLBackend: AppBackend {
+    public class Widget {
+        private var createWithParent: (LVObject) -> LVObject
+        var widget: LVObject?
+
+        init(createWithParent: @escaping (LVObject) -> LVObject) {
+            self.createWithParent = createWithParent
+            widget = nil
+        }
+
+        func postCreationAction(_ action: @escaping (LVObject) -> Void) {
+            if let widget = widget {
+                action(widget)
+            } else {
+                let create = createWithParent
+                self.createWithParent = { parent in
+                    let widget = create(parent)
+                    action(widget)
+                    return widget
+                }
+            }
+        }
+
+        func create(withParent parent: LVObject) -> LVObject {
+            if let widget = widget {
+                return widget
+            }
+
+            let widget = createWithParent(parent)
+            self.widget = widget
+            return widget
+        }
+    }
+
+    public class Grid: Widget {
+        var rowCount = 0
+        var columnCount = 0
+    }
+
+    public init(appIdentifier: String) {}
+
+    public func run<AppRoot: App>(
+        _ app: AppRoot,
+        _ setViewGraph: @escaping (ViewGraph<AppRoot>) -> Void
+    ) where AppRoot.Backend == Self {
+        let runLoop = LVRunLoop.shared
+
+        let viewGraph = ViewGraph(for: app, backend: self)
+        setViewGraph(viewGraph)
+
+        // TODO: app.windowProperties
+        _ = viewGraph.rootNode.widget.create(withParent: LVScreen.active)
+
+        runLoop.run()
+    }
+
+    public func runInMainThread(action: @escaping () -> Void) {
+        DispatchQueue.main.async {
+            action()
+        }
+    }
+
+    public func show(_ widget: Widget) {}
+
+    public func createVStack(spacing: Int) -> Widget {
+        let grid = Grid { parent in
+            let grid = LVGrid(with: parent, rows: 0, columns: 1, padding: Int16(spacing))
+            grid.size = LVSize(width: 1 << 13 | 2001, height: 1 << 13 | 2001)
+            grid.center()
+            return grid
+        }
+        grid.columnCount = 1
+        return grid
+    }
+
+    public func addChild(_ child: Widget, toVStack container: Widget) {
+        container.postCreationAction { widget in
+            let rowCount = (container as! Grid).rowCount
+            let grid = widget as! LVGrid
+            grid.resize(rows: UInt8(rowCount + 1), columns: 1)
+            // LVGL grid coordinates have column before row (weird)
+            grid.set(cell: child.create(withParent: widget), at: (0, UInt8(rowCount)))
+            (container as! Grid).rowCount += 1
+        }
+    }
+
+    public func setSpacing(ofVStack container: Widget, to spacing: Int) {
+        container.postCreationAction { widget in
+            let rowCount = (container as! Grid).rowCount
+            let grid = widget as! LVGrid
+            grid.resize(rows: UInt8(rowCount), columns: 1, padding: Int16(spacing))
+        }
+    }
+
+    public func createHStack(spacing: Int) -> Widget {
+        let grid = Grid { parent in
+            let grid = LVGrid(with: parent, rows: 1, columns: 0, padding: Int16(spacing))
+            grid.size = LVSize(width: 1 << 13 | 2001, height: 1 << 13 | 2001)
+            grid.center()
+            return grid
+        }
+        grid.rowCount = 1
+        return grid
+    }
+
+    public func addChild(_ child: Widget, toHStack container: Widget) {
+        container.postCreationAction { widget in
+            let columnCount = (container as! Grid).columnCount
+            let grid = widget as! LVGrid
+            grid.resize(rows: 1, columns: UInt8(columnCount + 1))
+            // LVGL grid coordinates have column before row (weird)
+            grid.set(cell: child.create(withParent: widget), at: (UInt8(columnCount), 0))
+            (container as! Grid).columnCount += 1
+        }
+    }
+
+    public func setSpacing(ofHStack container: Widget, to spacing: Int) {
+        container.postCreationAction { widget in
+            let columnCount = (container as! Grid).columnCount
+            let grid = widget as! LVGrid
+            grid.resize(rows: 1, columns: UInt8(columnCount), padding: Int16(spacing))
+        }
+    }
+
+    public func createTextView(content: String, shouldWrap: Bool) -> Widget {
+        return Widget { parent in
+            let label = LVLabel(with: parent)
+            label.text = content
+            return label
+        }
+    }
+
+    public func setContent(ofTextView textView: Widget, to content: String) {
+        textView.postCreationAction { widget in
+            (widget as! LVLabel).text = content
+        }
+    }
+
+    public func setWrap(ofTextView textView: Widget, to shouldWrap: Bool) {
+        // TODO: Implement text wrap option
+    }
+
+    public func createButton(label: String, action: @escaping () -> Void) -> Widget {
+        return Widget { parent in
+            let button = LVButton(with: parent)
+            let buttonLabel = LVLabel(with: button)
+            buttonLabel.text = label
+            buttonLabel.center()
+            button.onEvent = { event in
+                if event.code == LV_EVENT_PRESSED {
+                    action()
+                }
+            }
+            return button
+        }
+    }
+
+    public func setLabel(ofButton button: Widget, to label: String) {
+        button.postCreationAction { widget in
+            let widget = widget as! LVButton
+            (widget.child(at: 0)! as! LVLabel).text = label
+        }
+    }
+
+    public func setAction(ofButton button: Widget, to action: @escaping () -> Void) {
+        button.postCreationAction { widget in
+            let widget = widget as! LVButton
+            widget.onEvent = { event in
+                if event.code == LV_EVENT_PRESSED {
+                    action()
+                }
+            }
+        }
+    }
+}