macOS: inherit font size when creating new tab

This is one part of #281.

include/ghostty.h

@@ -233,6 +233,7 @@ typedef enum {
 typedef enum {
     GHOSTTY_BINDING_COPY_TO_CLIPBOARD,
     GHOSTTY_BINDING_PASTE_FROM_CLIPBOARD,
+    GHOSTTY_BINDING_NEW_TAB,
 } ghostty_binding_action_e;
 
 // Fully defined types. This MUST be kept in sync with equivalent Zig
@@ -242,6 +243,7 @@ typedef struct {
     void *userdata;
     void *nsview;
     double scale_factor;
+    uint8_t font_size;
 } ghostty_surface_config_s;
 
 typedef void (*ghostty_runtime_wakeup_cb)(void *);
@@ -254,6 +256,7 @@ typedef void (*ghostty_runtime_close_surface_cb)(void *, bool);
 typedef void (*ghostty_runtime_focus_split_cb)(void *, ghostty_split_focus_direction_e);
 typedef void (*ghostty_runtime_goto_tab_cb)(void *, int32_t);
 typedef void (*ghostty_runtime_toggle_fullscreen_cb)(void *, bool);
+typedef void (*ghostty_runtime_new_tab_cb)(void *, uint8_t);
 
 typedef struct {
     void *userdata;
@@ -268,6 +271,7 @@ typedef struct {
     ghostty_runtime_focus_split_cb focus_split_cb;
     ghostty_runtime_goto_tab_cb goto_tab_cb;
     ghostty_runtime_toggle_fullscreen_cb toggle_fullscreen_cb;
+    ghostty_runtime_new_tab_cb new_tab_cb;
 } ghostty_runtime_config_s;
 
 //-------------------------------------------------------------------

macos/Sources/AppDelegate.swift

@@ -1,6 +1,7 @@
 import AppKit
 import OSLog
 import GhosttyKit
+import SwiftUI
 
 @NSApplicationMain
 class AppDelegate: NSObject, NSApplicationDelegate, ObservableObject {
@@ -24,6 +25,22 @@ class AppDelegate: NSObject, NSApplicationDelegate, ObservableObject {
         super.init()
         
         windowManager = PrimaryWindowManager(ghostty: self.ghostty)
+        
+        // Register self as observer for the NewTab notification that
+        // is triggered via callback from Zig code.
+        NotificationCenter.default.addObserver(
+            self,
+            selector: #selector(onNewTab),
+            name: Ghostty.Notification.ghosttyNewTab,
+            object: nil)
+    }
+    
+    deinit {
+        // Clean up the observer.
+        NotificationCenter.default.removeObserver(
+            self,
+            name: Ghostty.Notification.ghosttyNewTab,
+            object: nil)
     }
     
     func applicationDidFinishLaunching(_ notification: Notification) {
@@ -81,13 +98,30 @@ class AppDelegate: NSObject, NSApplicationDelegate, ObservableObject {
     }
     
     @IBAction func newTab(_ sender: Any?) {
-        if let existingWindow = windowManager.mainWindow {
+        if windowManager.mainWindow != nil {
-            windowManager.addNewTab(to: existingWindow)
+            guard let surface = focusedSurface() else { return }
+            ghostty.newTab(surface: surface)
         } else {
             windowManager.addNewWindow()
         }
     }
     
+    @objc private func onNewTab(notification: SwiftUI.Notification) {
+        guard let surfaceView = notification.object as? Ghostty.SurfaceView else { return }
+        guard let window = surfaceView.window else { return }
+        
+        let fontSizeAny = notification.userInfo?[Ghostty.Notification.NewTabKey]
+        let fontSize = fontSizeAny as? UInt8
+        
+        if fontSize != nil {
+            // Add the new tab to the window with the given font size.
+            windowManager.addNewTab(to: window, withFontSize: fontSize)
+        } else {
+            // No font size specified, just add new tab.
+            windowManager.addNewTab(to: window)
+        }
+    }
+    
     @IBAction func closeWindow(_ sender: Any) {
         guard let currentWindow = NSApp.keyWindow else { return }
         currentWindow.close()

macos/Sources/Features/Primary Window/PrimaryView.swift

@@ -11,6 +11,9 @@ struct PrimaryView: View {
     // We need this to report back up the app controller which surface in this view is focused.
     let focusedSurfaceWrapper: FocusedSurfaceWrapper
     
+    // TODO: Document this
+    let fontSize: UInt8?
+    
     // We need access to our window to know if we're the key window to determine
     // if we show the quit confirmation or not.
     @State private var window: NSWindow?
@@ -71,7 +74,7 @@ struct PrimaryView: View {
                 self.appDelegate.confirmQuit = $0
             })
             
-            Ghostty.TerminalSplit(onClose: Self.closeWindow)
+            Ghostty.TerminalSplit(onClose: Self.closeWindow, fontSize: self.fontSize)
                 .ghosttyApp(ghostty.app!)
                 .background(WindowAccessor(window: $window))
                 .onReceive(gotoTab) { onGotoTab(notification: $0) }

macos/Sources/Features/Primary Window/PrimaryWindow.swift

@@ -16,7 +16,7 @@ class FocusedSurfaceWrapper {
 class PrimaryWindow: NSWindow {
     var focusedSurfaceWrapper: FocusedSurfaceWrapper = FocusedSurfaceWrapper()
 
-    static func create(ghostty: Ghostty.AppState, appDelegate: AppDelegate) -> PrimaryWindow {
+    static func create(ghostty: Ghostty.AppState, appDelegate: AppDelegate, fontSize: UInt8? = nil) -> PrimaryWindow {
         let window = PrimaryWindow(
             contentRect: NSRect(x: 0, y: 0, width: 800, height: 600),
             styleMask: [.titled, .closable, .miniaturizable, .resizable],
@@ -27,7 +27,9 @@ class PrimaryWindow: NSWindow {
         window.contentView = NSHostingView(rootView: PrimaryView(
             ghostty: ghostty,
             appDelegate: appDelegate,
-            focusedSurfaceWrapper: window.focusedSurfaceWrapper))
+            focusedSurfaceWrapper: window.focusedSurfaceWrapper,
+            fontSize: fontSize
+        ))
         
         // We do want to cascade when new windows are created
         window.windowController?.shouldCascadeWindows = true

macos/Sources/Features/Primary Window/PrimaryWindowController.swift

@@ -14,6 +14,7 @@ class PrimaryWindowController: NSWindowController {
     override func newWindowForTab(_ sender: Any?) {
         guard let window = self.window else { preconditionFailure("Expected window to be loaded") }
         guard let manager = self.windowManager else { return }
+        // TODO: We need to call to Zig code here so we can get the surface
         manager.addNewTab(to: window)
     }
 }

macos/Sources/Features/Primary Window/PrimaryWindowManager.swift

@@ -61,16 +61,16 @@ class PrimaryWindowManager {
         newWindow.makeKeyAndOrderFront(nil)
     }
     
-    func addNewTab(to window: NSWindow) {
+    func addNewTab(to window: NSWindow, withFontSize fontSize: UInt8? = nil) {
-        guard let controller = createWindowController() else { return }
+        guard let controller = createWindowController(withFontSize: fontSize) else { return }
         guard let newWindow = addManagedWindow(windowController: controller)?.window else { return  }
         window.addTabbedWindow(newWindow, ordered: .above)
         newWindow.makeKeyAndOrderFront(nil)
     }
 
-    private func createWindowController() -> PrimaryWindowController? {
+    private func createWindowController(withFontSize fontSize: UInt8? = nil) -> PrimaryWindowController? {
         guard let appDelegate = NSApplication.shared.delegate as? AppDelegate else { return nil }
-        let window = PrimaryWindow.create(ghostty: ghostty, appDelegate: appDelegate)
+        let window = PrimaryWindow.create(ghostty: ghostty, appDelegate: appDelegate, fontSize: fontSize)
         Self.lastCascadePoint = window.cascadeTopLeft(from: Self.lastCascadePoint)
         let controller = PrimaryWindowController(window: window)
         controller.windowManager = self

macos/Sources/Ghostty/AppState.swift

@@ -64,7 +64,8 @@ extension Ghostty {
                 close_surface_cb: { userdata, processAlive in AppState.closeSurface(userdata, processAlive: processAlive) },
                 focus_split_cb: { userdata, direction in AppState.focusSplit(userdata, direction: direction) },
                 goto_tab_cb: { userdata, n in AppState.gotoTab(userdata, n: n) },
-                toggle_fullscreen_cb: { userdata, nonNativeFullscreen in AppState.toggleFullscreen(userdata, useNonNativeFullscreen: nonNativeFullscreen) }
+                toggle_fullscreen_cb: { userdata, nonNativeFullscreen in AppState.toggleFullscreen(userdata, useNonNativeFullscreen: nonNativeFullscreen) },
+                new_tab_cb: { userdata, fontSize in AppState.newTab(userdata, fontSize: fontSize) }
             )
 
             // Create the ghostty app.
@@ -137,6 +138,10 @@ extension Ghostty {
             ghostty_surface_request_close(surface)
         }
         
+        func newTab(surface: ghostty_surface_t) {
+            ghostty_surface_binding_action(surface, GHOSTTY_BINDING_NEW_TAB, nil)
+        }
+        
         func split(surface: ghostty_surface_t, direction: ghostty_split_direction_e) {
             ghostty_surface_split(surface, direction)
         }
@@ -258,6 +263,17 @@ extension Ghostty {
             )
         }
         
+        static func newTab(_ userdata: UnsafeMutableRawPointer?, fontSize: UInt8) {
+            guard let surface = self.surfaceUserdata(from: userdata) else { return }
+            NotificationCenter.default.post(
+                name: Notification.ghosttyNewTab,
+                object: surface,
+                userInfo: [
+                    Notification.NewTabKey: fontSize,
+                ]
+            )
+        }
+        
         /// Returns the GhosttyState from the given userdata value.
         static private func appState(fromSurface userdata: UnsafeMutableRawPointer?) -> AppState? {
             let surfaceView = Unmanaged<SurfaceView>.fromOpaque(userdata!).takeUnretainedValue()

macos/Sources/Ghostty/Ghostty.SplitView.swift

@@ -8,10 +8,11 @@ extension Ghostty {
     struct TerminalSplit: View {
         @Environment(\.ghosttyApp) private var app
         let onClose: (() -> Void)?
+        let fontSize: UInt8?
         
         var body: some View {
             if let app = app {
-                TerminalSplitRoot(app: app, onClose: onClose)
+                TerminalSplitRoot(app: app, onClose: onClose, fontSize: fontSize)
             }
         }
     }
@@ -67,9 +68,9 @@ extension Ghostty {
             @Published var surface: SurfaceView
             
             /// Initialize a new leaf which creates a new terminal surface.
-            init(_ app: ghostty_app_t) {
+            init(_ app: ghostty_app_t, _ fontSize: UInt8?) {
                 self.app = app
-                self.surface = SurfaceView(app)
+                self.surface = SurfaceView(app, fontSize)
             }
         }
         
@@ -87,7 +88,7 @@ extension Ghostty {
                 // Initially, both topLeft and bottomRight are in the "nosplit"
                 // state since this is a new split.
                 self.topLeft = .noSplit(from)
-                self.bottomRight = .noSplit(.init(app))
+                self.bottomRight = .noSplit(.init(app, nil))
             }
         }
         
@@ -141,12 +142,14 @@ extension Ghostty {
         @State private var node: SplitNode
         @State private var requestClose: Bool = false
         let onClose: (() -> Void)?
+        let fontSize: UInt8?
         
         @FocusedValue(\.ghosttySurfaceTitle) private var surfaceTitle: String?
         
-        init(app: ghostty_app_t, onClose: (() ->Void)? = nil) {
+        init(app: ghostty_app_t, onClose: (() ->Void)? = nil, fontSize: UInt8? = nil) {
             self.onClose = onClose
-            _node = State(wrappedValue: SplitNode.noSplit(.init(app)))
+            self.fontSize = fontSize
+            _node = State(wrappedValue: SplitNode.noSplit(.init(app, fontSize)))
         }
         
         var body: some View {

macos/Sources/Ghostty/Package.swift

@@ -78,6 +78,10 @@ extension Ghostty.Notification {
     /// Goto tab. Has tab index in the userinfo.
     static let ghosttyGotoTab = Notification.Name("com.mitchellh.ghostty.gotoTab")
     static let GotoTabKey = ghosttyGotoTab.rawValue
+    
+    /// New tab. Has font size of currently focused surface in the userinfo.
+    static let ghosttyNewTab = Notification.Name("com.mitchellh.ghostty.newTab")
+    static let NewTabKey = ghosttyNewTab.rawValue
 
     /// Toggle fullscreen of current window
     static let ghosttyToggleFullscreen = Notification.Name("com.mitchellh.ghostty.toggleFullscreen")

macos/Sources/Ghostty/SurfaceView.swift

@@ -24,7 +24,7 @@ extension Ghostty {
         @StateObject private var surfaceView: SurfaceView
         
         init(_ app: ghostty_app_t, @ViewBuilder content: @escaping ((SurfaceView) -> Content)) {
-            _surfaceView = StateObject(wrappedValue: SurfaceView(app))
+            _surfaceView = StateObject(wrappedValue: SurfaceView(app, nil))
             self.content = content
         }
         
@@ -137,7 +137,7 @@ extension Ghostty {
         // so we'll use that to tell ghostty to refresh.
         override var wantsUpdateLayer: Bool { return true }
         
-        init(_ app: ghostty_app_t) {
+        init(_ app: ghostty_app_t, _ fontSize: UInt8?) {
             self.markedText = NSMutableAttributedString()
             
             // Initialize with some default frame size. The important thing is that this
@@ -149,7 +149,8 @@ extension Ghostty {
             var surface_cfg = ghostty_surface_config_s(
                 userdata: Unmanaged.passUnretained(self).toOpaque(),
                 nsview: Unmanaged.passUnretained(self).toOpaque(),
-                scale_factor: NSScreen.main!.backingScaleFactor)
+                scale_factor: NSScreen.main!.backingScaleFactor,
+                font_size: fontSize ?? 0)
             guard let surface = ghostty_surface_new(app, &surface_cfg) else {
                 self.error = AppError.surfaceCreateError
                 return

src/apprt/embedded.zig

@@ -70,6 +70,10 @@ pub const App = struct {
 
         /// Toggle fullscreen for current window.
         toggle_fullscreen: ?*const fn (SurfaceUD, bool) callconv(.C) void = null,
+
+        /// New tab with desired font size in points
+        /// TODO: u8 should be something that's nullable
+        new_tab: ?*const fn (SurfaceUD, u8) callconv(.C) void = null,
     };
 
     core_app: *CoreApp,
@@ -166,6 +170,9 @@ pub const Surface = struct {
 
         /// The scale factor of the screen.
         scale_factor: f64 = 1,
+
+        /// The font size to inherit. If 0, default font size will be used.
+        font_size: u8 = 0,
     };
 
     pub fn init(self: *Surface, app: *App, opts: Options) !void {
@@ -191,6 +198,13 @@ pub const Surface = struct {
         var config = try apprt.surface.newConfig(app.core_app, app.config);
         defer config.deinit();
 
+        // Overwrite the config for this new surface if we need to set a font
+        // size based on parent.
+        // TODO: Is this super hacky?
+        if (opts.font_size != 0) {
+            config.@"font-size" = opts.font_size;
+        }
+
         // Initialize our surface right away. We're given a view that is
         // ready to use.
         try self.core_surface.init(
@@ -580,6 +594,22 @@ pub const Surface = struct {
         func(self.opts.userdata, nonNativeFullscreen);
     }
 
+    pub fn newTab(self: *const Surface) !void {
+        const func = self.app.opts.new_tab orelse {
+            log.info("runtime embedder does not support new_tab", .{});
+            return;
+        };
+
+        // TODO: Do we check this here? Or do we check this in embedder?
+        //
+        const font_size: u8 = font_size: {
+            if (!self.app.config.@"window-inherit-font-size") break :font_size 0;
+            break :font_size @intCast(self.core_surface.font_size.points);
+        };
+
+        func(self.opts.userdata, font_size);
+    }
+
     /// The cursor position from the host directly is in screen coordinates but
     /// all our interface works in pixels.
     fn cursorPosToPixels(self: *const Surface, pos: apprt.CursorPos) !apprt.CursorPos {
@@ -804,6 +834,7 @@ pub const CAPI = struct {
         const action: input.Binding.Action = switch (key) {
             .copy_to_clipboard => .{ .copy_to_clipboard = {} },
             .paste_from_clipboard => .{ .paste_from_clipboard = {} },
+            .new_tab => .{ .new_tab = {} },
         };
 
         ptr.core_surface.performBindingAction(action) catch |err| {

src/input/Binding.zig

@@ -276,6 +276,7 @@ pub const Action = union(enum) {
 pub const Key = enum(c_int) {
     copy_to_clipboard,
     paste_from_clipboard,
+    new_tab,
 };
 
 /// Trigger is the associated key state that can trigger an action.