introduce split-preserve-zoom config to maintain zoomed splits during navigation

macos/Sources/Features/Terminal/BaseTerminalController.swift

@@ -621,9 +621,14 @@ class BaseTerminalController: NSWindowController,
             return
         }
 
-        // Remove the zoomed state for this surface tree.
         if surfaceTree.zoomed != nil {
-            surfaceTree = .init(root: surfaceTree.root, zoomed: nil)
+            if derivedConfig.splitPreserveZoom.contains(.navigation) {
+                surfaceTree = SplitTree(
+                    root: surfaceTree.root,
+                    zoomed: surfaceTree.root?.node(view: nextSurface))
+            } else {
+                surfaceTree = SplitTree(root: surfaceTree.root, zoomed: nil)
+            }
         }
 
         // Move focus to the next surface
@@ -1188,17 +1193,20 @@ class BaseTerminalController: NSWindowController,
         let macosTitlebarProxyIcon: Ghostty.MacOSTitlebarProxyIcon
         let windowStepResize: Bool
         let focusFollowsMouse: Bool
+        let splitPreserveZoom: Ghostty.Config.SplitPreserveZoom
 
         init() {
             self.macosTitlebarProxyIcon = .visible
             self.windowStepResize = false
             self.focusFollowsMouse = false
+            self.splitPreserveZoom = .init()
         }
 
         init(_ config: Ghostty.Config) {
             self.macosTitlebarProxyIcon = config.macosTitlebarProxyIcon
             self.windowStepResize = config.windowStepResize
             self.focusFollowsMouse = config.focusFollowsMouse
+            self.splitPreserveZoom = config.splitPreserveZoom
         }
     }
 }

macos/Sources/Ghostty/Ghostty.Config.swift

@@ -124,6 +124,14 @@ extension Ghostty {
             return .init(rawValue: v)
         }
 
+        var splitPreserveZoom: SplitPreserveZoom {
+            guard let config = self.config else { return .init() }
+            var v: CUnsignedInt = 0
+            let key = "split-preserve-zoom"
+            guard ghostty_config_get(config, &v, key, UInt(key.count)) else { return .init() }
+            return .init(rawValue: v)
+        }
+
         var initialWindow: Bool {
             guard let config = self.config else { return true }
             var v = true;
@@ -690,6 +698,12 @@ extension Ghostty.Config {
         static let border = BellFeatures(rawValue: 1 << 4)
     }
 
+    struct SplitPreserveZoom: OptionSet {
+        let rawValue: CUnsignedInt
+
+        static let navigation = SplitPreserveZoom(rawValue: 1 << 0)
+    }
+    
     enum MacDockDropBehavior: String {
         case new_tab = "new-tab"
         case new_window = "new-window"

src/apprt/gtk/class/split_tree.zig

@@ -340,6 +340,35 @@ pub const SplitTree = extern struct {
         const surface = tree.nodes[target.idx()].leaf;
         surface.grabFocus();
 
+        // We also need to setup our last_focused to this because if we
+        // trigger a tree change like below, the grab focus above never
+        // actually triggers in time to set this and this ensures we
+        // grab focus to the right thing.
+        const old_last_focused = self.private().last_focused.get();
+        defer if (old_last_focused) |v| v.unref(); // unref strong ref from get
+        self.private().last_focused.set(surface);
+        errdefer self.private().last_focused.set(old_last_focused);
+
+        if (tree.zoomed != null) {
+            const app = Application.default();
+            const config_obj = app.getConfig();
+            defer config_obj.unref();
+            const config = config_obj.get();
+
+            if (!config.@"split-preserve-zoom".navigation) {
+                tree.zoomed = null;
+            } else {
+                tree.zoom(target);
+            }
+
+            // When the zoom state changes our tree state changes and
+            // we need to send the proper notifications to trigger
+            // relayout.
+            const object = self.as(gobject.Object);
+            object.notifyByPspec(properties.tree.impl.param_spec);
+            object.notifyByPspec(properties.@"is-zoomed".impl.param_spec);
+        }
+
         return true;
     }
 

src/config/Config.zig

@@ -985,6 +985,14 @@ palette: Palette = .{},
 /// Available since: 1.1.0
 @"split-divider-color": ?Color = null,
 
+/// Control when Ghostty preserves the zoomed state of a split. This is a packed
+/// struct so more options can be added in the future. The `navigation` option
+/// keeps the current split zoomed when split navigation (`goto_split`) changes
+/// the focused split.
+///
+/// Example: `split-preserve-zoom = navigation`
+@"split-preserve-zoom": SplitPreserveZoom = .{},
+
 /// The foreground and background color for search matches. This only applies
 /// to non-focused search matches, also known as candidate matches.
 ///
@@ -7423,6 +7431,10 @@ pub const ShellIntegrationFeatures = packed struct {
     path: bool = true,
 };
 
+pub const SplitPreserveZoom = packed struct {
+    navigation: bool = false,
+};
+
 pub const RepeatableCommand = struct {
     value: std.ArrayListUnmanaged(inputpkg.Command) = .empty,
 

src/config/c_get.zig

@@ -222,3 +222,19 @@ test "c_get: background-blur" {
         try testing.expectEqual(-2, cval);
     }
 }
+
+test "c_get: split-preserve-zoom" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+
+    var c = try Config.default(alloc);
+    defer c.deinit();
+
+    var bits: c_uint = undefined;
+    try testing.expect(get(&c, .@"split-preserve-zoom", @ptrCast(&bits)));
+    try testing.expectEqual(@as(c_uint, 0), bits);
+
+    c.@"split-preserve-zoom".navigation = true;
+    try testing.expect(get(&c, .@"split-preserve-zoom", @ptrCast(&bits)));
+    try testing.expectEqual(@as(c_uint, 1), bits);
+}