macos: listen for color change property to update window appearance

macos/Sources/Features/Terminal/TerminalController.swift

@@ -1,6 +1,7 @@
 import Foundation
 import Cocoa
 import SwiftUI
+import Combine
 import GhosttyKit
 
 /// A classic, tabbed terminal experience.
@@ -23,6 +24,9 @@ class TerminalController: BaseTerminalController {
     /// The configuration derived from the Ghostty config so we don't need to rely on references.
     private var derivedConfig: DerivedConfig
 
+    /// The notification cancellable for focused surface property changes.
+    private var surfaceAppearanceCancellables: Set<AnyCancellable> = []
+
     init(_ ghostty: Ghostty.App,
          withBaseConfig base: Ghostty.SurfaceConfiguration? = nil,
          withSurfaceTree tree: Ghostty.SplitNode? = nil
@@ -225,7 +229,7 @@ class TerminalController: BaseTerminalController {
 
         // The titlebar is always updated. We don't need to worry about opacity
         // because we handle it here.
-        let backgroundColor = OSColor(surfaceConfig.backgroundColor)
+        let backgroundColor = OSColor(focusedSurface?.backgroundColor ?? surfaceConfig.backgroundColor)
         window.titlebarColor = backgroundColor.withAlphaComponent(surfaceConfig.backgroundOpacity)
 
         if (window.isOpaque) {
@@ -536,10 +540,31 @@ class TerminalController: BaseTerminalController {
     override func focusedSurfaceDidChange(to: Ghostty.SurfaceView?) {
         super.focusedSurfaceDidChange(to: to)
 
+        // We always cancel our event listener
+        surfaceAppearanceCancellables.removeAll()
+
         // When our focus changes, we update our window appearance based on the
         // currently focused surface.
         guard let focusedSurface else { return }
         syncAppearance(focusedSurface.derivedConfig)
+
+        // We also want to get notified of certain changes to update our appearance.
+        focusedSurface.$derivedConfig
+            .sink { [weak self, weak focusedSurface] _ in self?.syncAppearanceOnPropertyChange(focusedSurface) }
+            .store(in: &surfaceAppearanceCancellables)
+        focusedSurface.$backgroundColor
+            .sink { [weak self, weak focusedSurface] _ in self?.syncAppearanceOnPropertyChange(focusedSurface) }
+            .store(in: &surfaceAppearanceCancellables)
+    }
+
+    private func syncAppearanceOnPropertyChange(_ surface: Ghostty.SurfaceView?) {
+        guard let surface else { return }
+        DispatchQueue.main.async { [weak self, weak surface] in
+            guard let surface else { return }
+            guard let self else { return }
+            guard self.focusedSurface == surface else { return }
+            self.syncAppearance(surface.derivedConfig)
+        }
     }
 
     //MARK: - Notifications

macos/Sources/Ghostty/Ghostty.Action.swift

@@ -1,3 +1,4 @@
+import SwiftUI
 import GhosttyKit
 
 extension Ghostty {
@@ -5,6 +6,33 @@ extension Ghostty {
 }
 
 extension Ghostty.Action {
+    struct ColorChange {
+        let kind: Kind
+        let color: Color
+
+        enum Kind {
+            case foreground
+            case background
+            case cursor
+            case palette(index: UInt8)
+        }
+
+        init(c: ghostty_action_color_change_s) {
+            switch (c.kind) {
+            case GHOSTTY_ACTION_COLOR_KIND_FOREGROUND:
+                self.kind = .foreground
+            case GHOSTTY_ACTION_COLOR_KIND_BACKGROUND:
+                self.kind = .background
+            case GHOSTTY_ACTION_COLOR_KIND_CURSOR:
+                self.kind = .cursor
+            default:
+                self.kind = .palette(index: UInt8(c.kind.rawValue))
+            }
+
+            self.color = Color(red: Double(c.r) / 255, green: Double(c.g) / 255, blue: Double(c.b) / 255)
+        }
+    }
+
     struct MoveTab {
         let amount: Int
 

macos/Sources/Ghostty/Ghostty.App.swift

@@ -515,7 +515,8 @@ extension Ghostty {
                 configChange(app, target: target, v: action.action.config_change)
 
             case GHOSTTY_ACTION_COLOR_CHANGE:
-                fallthrough
+                colorChange(app, target: target, change: action.action.color_change)
+
             case GHOSTTY_ACTION_CLOSE_ALL_WINDOWS:
                 fallthrough
             case GHOSTTY_ACTION_TOGGLE_TAB_OVERVIEW:
@@ -1188,6 +1189,32 @@ extension Ghostty {
                 }
             }
 
+        private static func colorChange(
+            _ app: ghostty_app_t,
+            target: ghostty_target_s,
+            change: ghostty_action_color_change_s) {
+                switch (target.tag) {
+                case GHOSTTY_TARGET_APP:
+                    Ghostty.logger.warning("color change does nothing with an app target")
+                    return
+
+                case GHOSTTY_TARGET_SURFACE:
+                    guard let surface = target.target.surface else { return }
+                    guard let surfaceView = self.surfaceView(from: surface) else { return }
+                    NotificationCenter.default.post(
+                        name: .ghosttyColorDidChange,
+                        object: surfaceView,
+                        userInfo: [
+                            SwiftUI.Notification.Name.GhosttyColorChangeKey: Action.ColorChange(c: change)
+                        ]
+                    )
+
+                default:
+                    assertionFailure()
+                }
+        }
+
+
         // MARK: User Notifications
 
         /// Handle a received user notification. This is called when a user notification is clicked or dismissed by the user

macos/Sources/Ghostty/Package.swift

@@ -210,6 +210,10 @@ extension Notification.Name {
     static let ghosttyConfigDidChange = Notification.Name("com.mitchellh.ghostty.configDidChange")
     static let GhosttyConfigChangeKey = ghosttyConfigDidChange.rawValue
 
+    /// Color change. Object is the surface changing.
+    static let ghosttyColorDidChange = Notification.Name("com.mitchellh.ghostty.ghosttyColorDidChange")
+    static let GhosttyColorChangeKey = ghosttyColorDidChange.rawValue
+
     /// Goto tab. Has tab index in the userinfo.
     static let ghosttyMoveTab = Notification.Name("com.mitchellh.ghostty.moveTab")
     static let GhosttyMoveTabKey = ghosttyMoveTab.rawValue

macos/Sources/Ghostty/SurfaceView_AppKit.swift

@@ -51,6 +51,10 @@ extension Ghostty {
         /// The configuration derived from the Ghostty config so we don't need to rely on references.
         @Published private(set) var derivedConfig: DerivedConfig
 
+        /// The background color within the color palette of the surface. This is only set if it is
+        /// dynamically updated. Otherwise, the background color is the default background color.
+        @Published private(set) var backgroundColor: Color? = nil
+
         // An initial size to request for a window. This will only affect
         // then the view is moved to a new window.
         var initialSize: NSSize? = nil
@@ -152,6 +156,11 @@ extension Ghostty {
                 selector: #selector(ghosttyConfigDidChange(_:)),
                 name: .ghosttyConfigDidChange,
                 object: self)
+            center.addObserver(
+                self,
+                selector: #selector(ghosttyColorDidChange(_:)),
+                name: .ghosttyColorDidChange,
+                object: self)
             center.addObserver(
                 self,
                 selector: #selector(windowDidChangeScreen),
@@ -358,6 +367,21 @@ extension Ghostty {
             self.derivedConfig = DerivedConfig(config)
         }
 
+        @objc private func ghosttyColorDidChange(_ notification: SwiftUI.Notification) {
+            guard let change = notification.userInfo?[
+                SwiftUI.Notification.Name.GhosttyColorChangeKey
+            ] as? Ghostty.Action.ColorChange else { return }
+
+            switch (change.kind) {
+            case .background:
+                self.backgroundColor = change.color
+
+            default:
+                // We don't do anything for the other colors yet.
+                break
+            }
+        }
+
         @objc private func windowDidChangeScreen(notification: SwiftUI.Notification) {
             guard let window = self.window else { return }
             guard let object = notification.object as? NSWindow, window == object else { return }