Feat: SpringMotionPanel with SpringMotionWindowProtocol conformance

Sources/SpringMotionPanel.swift

@@ -0,0 +1,130 @@
+//
+//  SpringMotionPanel.swift
+//
+//
+//  Created by Oryna Semenets on 17.10.2024.
+//
+
+#if canImport(AppKit)
+
+import AppKit
+
+open class SpringMotionPanel: NSPanel {
+
+    /// Configuration that adjusts the spring physics behind the animation.
+    public var configuration: SpringConfiguration = .default {
+        didSet {
+            motionPhysics = .init(configuration: configuration, timeStep: 0.008)
+        }
+    }
+
+    // MARK: Private
+    private var destinationPoint: NSPoint? {
+        didSet {
+            startMotion()
+        }
+    }
+
+    private lazy var motionPhysics = SpringMotionPhysics(configuration: configuration, timeStep: 0.008)
+    private var currentMotionState: SpringMotionState?
+    private var displayLink: CVDisplayLink?
+    private var anchorWindowFrameObservation: NSKeyValueObservation?
+}
+
+// MARK: - API
+public extension SpringMotionPanel {
+
+    /// Moves the window to the specified point with spring animation.
+    ///
+    /// - Parameter point: a `CGPoint` that defines the window's destination and represents the window's center point.
+    func move(to point: NSPoint) {
+        destinationPoint = point
+    }
+
+    /// Starts following the given window with a certain offset from its center.
+    ///
+    /// - Parameter anchorWindow: an `NSWindow` that this window will follow.
+    /// - Parameter offsetFromCenter: the difference between this window's center and the anchor window's center.
+    func pinToWindow(_ anchorWindow: NSWindow, offsetFromCenter: NSPoint) {
+        unpinFromWindow()
+        move(to: anchorWindow.frame.center + offsetFromCenter)
+        anchorWindowFrameObservation = anchorWindow.observe(\.frame, changeHandler: { [weak self] _, _ in
+            self?.move(to: anchorWindow.frame.center + offsetFromCenter)
+        })
+    }
+
+    /// Stops following a previously followed window, if any.
+    func unpinFromWindow() {
+        anchorWindowFrameObservation?.invalidate()
+        anchorWindowFrameObservation = nil
+    }
+}
+
+// MARK: - Mouse events
+public extension SpringMotionPanel {
+
+    override func mouseDown(with event: NSEvent) {
+        super.mouseDown(with: event)
+        // Stop window from moving if the user grabbed it.
+        if isMovableByWindowBackground {
+            stopMotion()
+        }
+    }
+
+    override func mouseUp(with event: NSEvent) {
+        super.mouseUp(with: event)
+        // Continue movement after the user lets go.
+        if isMovableByWindowBackground {
+            startMotion()
+        }
+    }
+}
+
+// MARK: - Start/stop motion
+private extension SpringMotionPanel {
+
+    func startMotion() {
+        guard displayLink == nil,
+              let screenDescription = NSScreen.main?.deviceDescription,
+              let screenNumber = screenDescription[.init("NSScreenNumber")] as? NSNumber else { return }
+
+        CVDisplayLinkCreateWithCGDisplay(screenNumber.uint32Value, &displayLink)
+        guard let displayLink else { return }
+
+        CVDisplayLinkSetOutputHandler(displayLink) { [weak self] _, inNow, _, _, _ in
+            DispatchQueue.main.async { [weak self] in
+                guard let self, let destinationPoint else {
+                    self?.stopMotion()
+                    return
+                }
+
+                let currentState = currentMotionState ?? .init(position: frame.center, velocity: .zero)
+                let nextState = motionPhysics.calculateNextState(from: currentState, destinationPoint: destinationPoint)
+
+                if abs(nextState.velocity.horizontal) < 0.01 && abs(nextState.velocity.vertical) < 0.01 {
+                    stopMotion()
+                    return
+                }
+
+                self.setFrame(.init(x: nextState.position.x - frame.width / 2,
+                                    y: nextState.position.y - frame.height / 2,
+                                    width: frame.width,
+                                    height: frame.height), display: false)
+                currentMotionState = nextState
+            }
+
+            return kCVReturnSuccess
+        }
+
+        CVDisplayLinkStart(displayLink)
+    }
+
+    func stopMotion() {
+        guard let link = displayLink else { return }
+        CVDisplayLinkStop(link)
+        displayLink = nil
+        currentMotionState = nil
+    }
+}
+
+#endif