Add toggle_background_opacity action for macOS

include/ghostty.h

@@ -591,6 +591,7 @@ typedef enum {
   GHOSTTY_ACTION_TOGGLE_FULLSCREEN,
   GHOSTTY_ACTION_TOGGLE_TAB_OVERVIEW,
   GHOSTTY_ACTION_TOGGLE_WINDOW_DECORATIONS,
+  GHOSTTY_ACTION_TOGGLE_BACKGROUND_OPACITY,
   GHOSTTY_ACTION_TOGGLE_QUICK_TERMINAL,
   GHOSTTY_ACTION_TOGGLE_COMMAND_PALETTE,
   GHOSTTY_ACTION_TOGGLE_VISIBILITY,

macos/Sources/Ghostty/Ghostty.App.swift

@@ -550,6 +550,9 @@ extension Ghostty {
             case GHOSTTY_ACTION_RING_BELL:
                 ringBell(app, target: target)
 
+            case GHOSTTY_ACTION_TOGGLE_BACKGROUND_OPACITY:
+                toggleBackgroundOpacity(app, target: target)
+
             case GHOSTTY_ACTION_CLOSE_ALL_WINDOWS:
                 fallthrough
             case GHOSTTY_ACTION_TOGGLE_TAB_OVERVIEW:
@@ -1071,7 +1074,7 @@ extension Ghostty {
                 guard let surface = target.target.surface else { return }
                 guard let surfaceView = self.surfaceView(from: surface) else { return }
                 guard let window = surfaceView.window as? TerminalWindow else { return }
-                
+
                 switch (mode) {
                 case .on:
                     window.level = .floating
@@ -1509,6 +1512,24 @@ extension Ghostty {
                 }
         }
 
+        private static func toggleBackgroundOpacity(_ app: ghostty_app_t, target: ghostty_target_s) {
+            switch (target.tag) {
+            case GHOSTTY_TARGET_APP:
+                Ghostty.logger.warning("toggle_background_opacity does nothing with an app target")
+                return
+
+            case GHOSTTY_TARGET_SURFACE:
+                guard let surface = target.target.surface,
+                      let surfaceView = self.surfaceView(from: surface) else { return }
+                NotificationCenter.default.post(
+                    name: .ghosttyBackgroundOpacityDidToggle,
+                    object: surfaceView
+                )
+
+            default:
+                assertionFailure()
+            }
+        }
 
         // MARK: User Notifications
 

macos/Sources/Ghostty/Package.swift

@@ -263,6 +263,9 @@ extension Notification.Name {
     static let ghosttyColorDidChange = Notification.Name("com.mitchellh.ghostty.ghosttyColorDidChange")
     static let GhosttyColorChangeKey = ghosttyColorDidChange.rawValue
 
+    /// Background opacity toggle event
+    static let ghosttyBackgroundOpacityDidToggle = Notification.Name("com.mitchellh.ghostty.backgroundOpacityDidToggle")
+
     /// 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

@@ -203,6 +203,11 @@ extension Ghostty {
                 selector: #selector(windowDidChangeScreen),
                 name: NSWindow.didChangeScreenNotification,
                 object: nil)
+            center.addObserver(
+                self,
+                selector: #selector(ghosttyBackgroundOpacityDidToggle),
+                name: .ghosttyBackgroundOpacityDidToggle,
+                object: self)
 
             // Listen for local events that we need to know of outside of
             // single surface handlers.
@@ -591,6 +596,30 @@ extension Ghostty {
             }
         }
 
+        @objc private func ghosttyBackgroundOpacityDidToggle() {
+            guard self.derivedConfig.backgroundOpacity < 1 else { return }
+
+            // Toggle the window's background opacity
+            if let window = self.window as? TerminalWindow {
+                let newOpaque = !window.isOpaque
+                window.isOpaque = newOpaque
+
+                // Update the window background color based on opacity state
+                if newOpaque {
+                    window.backgroundColor = NSColor(self.derivedConfig.backgroundColor)
+                } else {
+                    // Use a very small alpha component to match Terminal.app's look
+                    window.backgroundColor = .white.withAlphaComponent(0.001)
+                    // Apply background blur
+                    if let app = (NSApplication.shared.delegate as? AppDelegate)?.ghostty.app {
+                        ghostty_set_window_background_blur(app, Unmanaged.passUnretained(window).toOpaque())
+                    }
+                }
+            } else {
+                Ghostty.logger.warning("toggle background opacity: no terminal window found")
+            }
+        }
+
         // MARK: - NSView
 
         override func becomeFirstResponder() -> Bool {

src/Surface.zig

@@ -4291,6 +4291,12 @@ pub fn performBindingAction(self: *Surface, action: input.Binding.Action) !bool
             {},
         ),
 
+        .toggle_background_opacity => return try self.rt_app.performAction(
+            .{ .surface = self },
+            .toggle_background_opacity,
+            {},
+        ),
+
         .toggle_tab_overview => return try self.rt_app.performAction(
             .{ .surface = self },
             .toggle_tab_overview,

src/apprt/action.zig

@@ -104,6 +104,9 @@ pub const Action = union(Key) {
     /// Toggle whether window directions are shown.
     toggle_window_decorations,
 
+    /// Toggle the background opacity of the target terminal.
+    toggle_background_opacity,
+
     /// Toggle the quick terminal in or out.
     toggle_quick_terminal,
 
@@ -267,6 +270,7 @@ pub const Action = union(Key) {
         toggle_fullscreen,
         toggle_tab_overview,
         toggle_window_decorations,
+        toggle_background_opacity,
         toggle_quick_terminal,
         toggle_command_palette,
         toggle_visibility,

src/apprt/glfw.zig

@@ -227,6 +227,7 @@ pub const App = struct {
             .close_tab,
             .toggle_tab_overview,
             .toggle_window_decorations,
+            .toggle_background_opacity,
             .toggle_quick_terminal,
             .toggle_command_palette,
             .toggle_visibility,

src/input/Binding.zig

@@ -439,6 +439,9 @@ pub const Action = union(enum) {
     /// This only works on macOS.
     toggle_window_float_on_top,
 
+    /// Toggle background opacity of window.
+    toggle_background_opacity: void,
+
     /// Toggle secure input mode on or off. This is used to prevent apps
     /// that monitor input from seeing what you type. This is useful for
     /// entering passwords or other sensitive information.
@@ -830,6 +833,7 @@ pub const Action = union(enum) {
             .toggle_fullscreen,
             .toggle_window_decorations,
             .toggle_window_float_on_top,
+            .toggle_background_opacity,
             .toggle_secure_input,
             .toggle_command_palette,
             .reset_window_size,