feat: finish ghostty pane backend integration

1 files changed, 1290 insertions, 0 deletions

diff --git a/vendor/libghostty-vt/src/apprt/gtk/class/split_tree.zig b/vendor/libghostty-vt/src/apprt/gtk/class/split_tree.zig
new file mode 100644
index 00000000..311fbd8a
--- /dev/null
+++ b/vendor/libghostty-vt/src/apprt/gtk/class/split_tree.zig
@@ -0,0 +1,1290 @@
+const std = @import("std");
+const assert = @import("../../../quirks.zig").inlineAssert;
+const Allocator = std.mem.Allocator;
+const adw = @import("adw");
+const gio = @import("gio");
+const glib = @import("glib");
+const gobject = @import("gobject");
+const gtk = @import("gtk");
+
+const configpkg = @import("../../../config.zig");
+const apprt = @import("../../../apprt.zig");
+const ext = @import("../ext.zig");
+const gresource = @import("../build/gresource.zig");
+const Common = @import("../class.zig").Common;
+const WeakRef = @import("../weak_ref.zig").WeakRef;
+const Application = @import("application.zig").Application;
+const CloseConfirmationDialog = @import("close_confirmation_dialog.zig").CloseConfirmationDialog;
+const Surface = @import("surface.zig").Surface;
+const SurfaceScrolledWindow = @import("surface_scrolled_window.zig").SurfaceScrolledWindow;
+
+const log = std.log.scoped(.gtk_ghostty_split_tree);
+
+pub const SplitTree = extern struct {
+    const Self = @This();
+    parent_instance: Parent,
+    pub const Parent = gtk.Box;
+    pub const getGObjectType = gobject.ext.defineClass(Self, .{
+        .name = "GhosttySplitTree",
+        .instanceInit = &init,
+        .classInit = &Class.init,
+        .parent_class = &Class.parent,
+        .private = .{ .Type = Private, .offset = &Private.offset },
+    });
+
+    pub const properties = struct {
+        /// The active surface is the surface that should be receiving all
+        /// surface-targeted actions. This is usually the focused surface,
+        /// but may also not be focused if the user has selected a non-surface
+        /// widget.
+        pub const @"active-surface" = struct {
+            pub const name = "active-surface";
+            const impl = gobject.ext.defineProperty(
+                name,
+                Self,
+                ?*Surface,
+                .{
+                    .accessor = gobject.ext.typedAccessor(
+                        Self,
+                        ?*Surface,
+                        .{
+                            .getter = getActiveSurface,
+                        },
+                    ),
+                },
+            );
+        };
+
+        pub const @"has-surfaces" = struct {
+            pub const name = "has-surfaces";
+            const impl = gobject.ext.defineProperty(
+                name,
+                Self,
+                bool,
+                .{
+                    .default = false,
+                    .accessor = gobject.ext.typedAccessor(
+                        Self,
+                        bool,
+                        .{
+                            .getter = getHasSurfaces,
+                        },
+                    ),
+                },
+            );
+        };
+
+        pub const @"is-zoomed" = struct {
+            pub const name = "is-zoomed";
+            const impl = gobject.ext.defineProperty(
+                name,
+                Self,
+                bool,
+                .{
+                    .default = false,
+                    .accessor = gobject.ext.typedAccessor(
+                        Self,
+                        bool,
+                        .{
+                            .getter = getIsZoomed,
+                        },
+                    ),
+                },
+            );
+        };
+
+        pub const tree = struct {
+            pub const name = "tree";
+            const impl = gobject.ext.defineProperty(
+                name,
+                Self,
+                ?*Surface.Tree,
+                .{
+                    .accessor = .{
+                        .getter = getTreeValue,
+                        .setter = setTreeValue,
+                    },
+                },
+            );
+        };
+
+        pub const @"is-split" = struct {
+            pub const name = "is-split";
+            const impl = gobject.ext.defineProperty(
+                name,
+                Self,
+                bool,
+                .{
+                    .default = false,
+                    .accessor = gobject.ext.typedAccessor(
+                        Self,
+                        bool,
+                        .{
+                            .getter = getIsSplit,
+                        },
+                    ),
+                },
+            );
+        };
+    };
+
+    pub const signals = struct {
+        /// Emitted whenever the tree property has changed, with access
+        /// to the previous and new values.
+        pub const changed = struct {
+            pub const name = "changed";
+            pub const connect = impl.connect;
+            const impl = gobject.ext.defineSignal(
+                name,
+                Self,
+                &.{ ?*const Surface.Tree, ?*const Surface.Tree },
+                void,
+            );
+        };
+    };
+
+    const Private = struct {
+        /// The tree datastructure containing all of our surface views.
+        tree: ?*Surface.Tree,
+
+        // Template bindings
+        tree_bin: *adw.Bin,
+
+        /// Last focused surface in the tree. We need this to handle various
+        /// tree change states.
+        last_focused: WeakRef(Surface) = .empty,
+
+        /// The source that we use to rebuild the tree. This is also
+        /// used to debounce updates.
+        rebuild_source: ?c_uint = null,
+
+        /// Used to store state about a pending surface close for the
+        /// close dialog.
+        pending_close: ?Surface.Tree.Node.Handle,
+
+        pub var offset: c_int = 0;
+    };
+
+    fn init(self: *Self, _: *Class) callconv(.c) void {
+        gtk.Widget.initTemplate(self.as(gtk.Widget));
+
+        // Initialize our actions
+        self.initActionMap();
+
+        // Initialize some basic state
+        const priv = self.private();
+        priv.pending_close = null;
+    }
+
+    fn initActionMap(self: *Self) void {
+        const s_variant_type = glib.ext.VariantType.newFor([:0]const u8);
+        defer s_variant_type.free();
+
+        const actions = [_]ext.actions.Action(Self){
+            // All of these will eventually take a target surface parameter.
+            // For now all our targets originate from the focused surface.
+            .init("new-split", actionNewSplit, s_variant_type),
+            .init("equalize", actionEqualize, null),
+            .init("zoom", actionZoom, null),
+        };
+
+        _ = ext.actions.addAsGroup(Self, self, "split-tree", &actions);
+    }
+
+    /// Create a new split in the given direction from the currently
+    /// active surface.
+    ///
+    /// If the tree is empty this will create a new tree with a new surface
+    /// and ignore the direction.
+    ///
+    /// The parent will be used as the parent of the surface regardless of
+    /// if that parent is in this split tree or not. This allows inheriting
+    /// surface properties from anywhere.
+    pub fn newSplit(
+        self: *Self,
+        direction: Surface.Tree.Split.Direction,
+        parent_: ?*Surface,
+        overrides: struct {
+            command: ?configpkg.Command = null,
+            working_directory: ?[:0]const u8 = null,
+            title: ?[:0]const u8 = null,
+
+            pub const none: @This() = .{};
+        },
+    ) Allocator.Error!void {
+        const alloc = Application.default().allocator();
+
+        // Create our new surface.
+        const surface: *Surface = .new(.{
+            .command = overrides.command,
+            .working_directory = overrides.working_directory,
+            .title = overrides.title,
+        });
+        defer surface.unref();
+        _ = surface.refSink();
+
+        // Inherit properly if we were asked to.
+        if (parent_) |p| {
+            if (p.core()) |core| {
+                surface.setParent(core, .split);
+            }
+        }
+
+        // Bind is-split property for new surface
+        _ = self.as(gobject.Object).bindProperty(
+            "is-split",
+            surface.as(gobject.Object),
+            "is-split",
+            .{ .sync_create = true },
+        );
+
+        // Create our tree
+        var single_tree = try Surface.Tree.init(alloc, surface);
+        defer single_tree.deinit();
+
+        // We want to move our focus to the new surface no matter what.
+        // But we need to be careful to restore state if we fail.
+        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 we have no tree yet, then this becomes our tree and we're done.
+        const old_tree = self.getTree() orelse {
+            self.setTree(&single_tree);
+            return;
+        };
+
+        // The handle we create the split relative to. Today this is the active
+        // surface but this might be the handle of the given parent if we want.
+        const handle = self.getActiveSurfaceHandle() orelse .root;
+
+        // Create our split!
+        var new_tree = try old_tree.split(
+            alloc,
+            handle,
+            direction,
+            0.5, // Always split equally for new splits
+            &single_tree,
+        );
+        defer new_tree.deinit();
+        log.debug(
+            "new split at={} direction={} old_tree={f} new_tree={f}",
+            .{ handle, direction, old_tree, &new_tree },
+        );
+
+        // Replace our tree
+        self.setTree(&new_tree);
+    }
+
+    pub fn resize(
+        self: *Self,
+        direction: Surface.Tree.Split.Direction,
+        amount: u16,
+    ) Allocator.Error!bool {
+        // Avoid useless work
+        if (amount == 0) return false;
+
+        const old_tree = self.getTree() orelse return false;
+        const active = self.getActiveSurfaceHandle() orelse return false;
+
+        // Get all our dimensions we're going to need to turn our
+        // amount into a percentage.
+        const priv = self.private();
+        const width = priv.tree_bin.as(gtk.Widget).getWidth();
+        const height = priv.tree_bin.as(gtk.Widget).getHeight();
+        if (width == 0 or height == 0) return false;
+        const width_f64: f64 = @floatFromInt(width);
+        const height_f64: f64 = @floatFromInt(height);
+        const amount_f64: f64 = @floatFromInt(amount);
+
+        // Get our ratio and use positive/neg for directions.
+        const ratio: f64 = switch (direction) {
+            .right => amount_f64 / width_f64,
+            .left => -(amount_f64 / width_f64),
+            .down => amount_f64 / height_f64,
+            .up => -(amount_f64 / height_f64),
+        };
+
+        const layout: Surface.Tree.Split.Layout = switch (direction) {
+            .left, .right => .horizontal,
+            .up, .down => .vertical,
+        };
+
+        var new_tree = try old_tree.resize(
+            Application.default().allocator(),
+            active,
+            layout,
+            @floatCast(ratio),
+        );
+        defer new_tree.deinit();
+        self.setTree(&new_tree);
+        return true;
+    }
+
+    /// Move focus from the currently focused surface to the given
+    /// direction. Returns true if focus switched to a new surface.
+    pub fn goto(self: *Self, to: Surface.Tree.Goto) bool {
+        const tree = self.getTree() orelse return false;
+        const active = self.getActiveSurfaceHandle() orelse return false;
+        const target = if (tree.goto(
+            Application.default().allocator(),
+            active,
+            to,
+        )) |handle_|
+            handle_ orelse return false
+        else |err| switch (err) {
+            // Nothing we can do in this scenario. This is highly unlikely
+            // since split trees don't use that much memory. The application
+            // is probably about to crash in other ways.
+            error.OutOfMemory => return false,
+        };
+
+        // If we aren't changing targets then we did nothing.
+        if (active == target) return false;
+
+        // Get the surface at the target location and grab focus.
+        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;
+    }
+
+    fn disconnectSurfaceHandlers(self: *Self) void {
+        const tree = self.getTree() orelse return;
+        var it = tree.iterator();
+        while (it.next()) |entry| {
+            const surface = entry.view;
+            _ = gobject.signalHandlersDisconnectMatched(
+                surface.as(gobject.Object),
+                .{ .data = true },
+                0,
+                0,
+                null,
+                null,
+                self,
+            );
+        }
+    }
+
+    fn connectSurfaceHandlers(self: *Self) void {
+        const tree = self.getTree() orelse return;
+        var it = tree.iterator();
+        while (it.next()) |entry| {
+            const surface = entry.view;
+            _ = Surface.signals.@"close-request".connect(
+                surface,
+                *Self,
+                surfaceCloseRequest,
+                self,
+                .{},
+            );
+            _ = gobject.Object.signals.notify.connect(
+                surface,
+                *Self,
+                propSurfaceFocused,
+                self,
+                .{ .detail = "focused" },
+            );
+        }
+    }
+
+    //---------------------------------------------------------------
+    // Properties
+
+    /// Returns true if this split tree needs confirmation before quitting based
+    /// on the various Ghostty configurations.
+    pub fn getNeedsConfirmQuit(self: *Self) bool {
+        const tree = self.getTree() orelse return false;
+        var it = tree.iterator();
+        while (it.next()) |entry| {
+            if (entry.view.core()) |core| {
+                if (core.needsConfirmQuit()) {
+                    return true;
+                }
+            }
+        }
+
+        return false;
+    }
+
+    /// Get the currently active surface. See the "active-surface" property.
+    /// This does not ref the value.
+    pub fn getActiveSurface(self: *Self) ?*Surface {
+        const tree = self.getTree() orelse return null;
+        const handle = self.getActiveSurfaceHandle() orelse return null;
+        return tree.nodes[handle.idx()].leaf;
+    }
+
+    fn getActiveSurfaceHandle(self: *Self) ?Surface.Tree.Node.Handle {
+        const tree = self.getTree() orelse return null;
+        var it = tree.iterator();
+        while (it.next()) |entry| {
+            if (entry.view.getFocused()) return entry.handle;
+        }
+
+        // If none are currently focused, the most previously focused
+        // surface (if it exists) is our active surface. This lets things
+        // like apprt actions and bell ringing continue to work in the
+        // background.
+        if (self.private().last_focused.get()) |v| {
+            defer v.unref();
+
+            // We need to find the handle of the last focused surface.
+            it = tree.iterator();
+            while (it.next()) |entry| {
+                if (entry.view == v) return entry.handle;
+            }
+        }
+
+        return null;
+    }
+
+    /// Returns the last focused surface in the tree.
+    pub fn getLastFocusedSurface(self: *Self) ?*Surface {
+        const surface = self.private().last_focused.get() orelse return null;
+        // We unref because get() refs the surface. We don't use the weakref
+        // in a multi-threaded context so this is safe.
+        surface.unref();
+        return surface;
+    }
+
+    pub fn getHasSurfaces(self: *Self) bool {
+        const tree: *const Surface.Tree = self.private().tree orelse &.empty;
+        return !tree.isEmpty();
+    }
+
+    pub fn getIsZoomed(self: *Self) bool {
+        const tree: *const Surface.Tree = self.private().tree orelse &.empty;
+        return tree.zoomed != null;
+    }
+
+    /// Get the tree data model that we're showing in this widget. This
+    /// does not clone the tree.
+    pub fn getTree(self: *Self) ?*Surface.Tree {
+        return self.private().tree;
+    }
+
+    /// Set the tree data model that we're showing in this widget. This
+    /// will clone the given tree.
+    pub fn setTree(self: *Self, tree_: ?*const Surface.Tree) void {
+        const priv = self.private();
+
+        // We always normalize our tree parameter so that empty trees
+        // become null so that we don't have to deal with callers being
+        // confused about that.
+        const tree: ?*const Surface.Tree = tree: {
+            const tree = tree_ orelse break :tree null;
+            if (tree.isEmpty()) break :tree null;
+            break :tree tree;
+        };
+
+        // Emit the signal so that handlers can witness both the before and
+        // after values of the tree.
+        signals.changed.impl.emit(
+            self,
+            null,
+            .{ priv.tree, tree },
+            null,
+        );
+
+        if (priv.tree) |old_tree| {
+            self.disconnectSurfaceHandlers();
+            ext.boxedFree(Surface.Tree, old_tree);
+            priv.tree = null;
+        }
+
+        if (tree) |new_tree| {
+            assert(priv.tree == null);
+            assert(!new_tree.isEmpty());
+            priv.tree = ext.boxedCopy(Surface.Tree, new_tree);
+            self.connectSurfaceHandlers();
+        }
+
+        self.as(gobject.Object).notifyByPspec(properties.tree.impl.param_spec);
+    }
+
+    fn getTreeValue(self: *Self, value: *gobject.Value) void {
+        gobject.ext.Value.set(
+            value,
+            self.private().tree,
+        );
+    }
+
+    fn setTreeValue(self: *Self, value: *const gobject.Value) void {
+        self.setTree(gobject.ext.Value.get(
+            value,
+            ?*Surface.Tree,
+        ));
+    }
+
+    pub fn getIsSplit(self: *Self) bool {
+        const tree: *const Surface.Tree = self.private().tree orelse &.empty;
+        if (tree.isEmpty()) return false;
+
+        const root_handle: Surface.Tree.Node.Handle = .root;
+        const root = tree.nodes[root_handle.idx()];
+        return switch (root) {
+            .leaf => false,
+            .split => true,
+        };
+    }
+
+    //---------------------------------------------------------------
+    // Virtual methods
+
+    fn dispose(self: *Self) callconv(.c) void {
+        const priv = self.private();
+        priv.last_focused.set(null);
+        if (priv.rebuild_source) |v| {
+            if (glib.Source.remove(v) == 0) {
+                log.warn("unable to remove rebuild source", .{});
+            }
+            priv.rebuild_source = null;
+        }
+
+        gtk.Widget.disposeTemplate(
+            self.as(gtk.Widget),
+            getGObjectType(),
+        );
+
+        gobject.Object.virtual_methods.dispose.call(
+            Class.parent,
+            self.as(Parent),
+        );
+    }
+
+    fn finalize(self: *Self) callconv(.c) void {
+        const priv = self.private();
+        if (priv.tree) |tree| {
+            ext.boxedFree(Surface.Tree, tree);
+            priv.tree = null;
+        }
+
+        gobject.Object.virtual_methods.finalize.call(
+            Class.parent,
+            self.as(Parent),
+        );
+    }
+
+    //---------------------------------------------------------------
+    // Signal handlers
+
+    pub fn actionNewSplit(
+        _: *gio.SimpleAction,
+        args_: ?*glib.Variant,
+        self: *Self,
+    ) callconv(.c) void {
+        const args = args_ orelse {
+            log.warn("split-tree.new-split called without a parameter", .{});
+            return;
+        };
+
+        var dir: ?[*:0]const u8 = null;
+        args.get("&s", &dir);
+
+        const direction = std.meta.stringToEnum(
+            Surface.Tree.Split.Direction,
+            std.mem.span(dir) orelse return,
+        ) orelse {
+            // Need to be defensive here since actions can be triggered externally.
+            log.warn("invalid split direction for split-tree.new-split: {s}", .{dir.?});
+            return;
+        };
+
+        self.newSplit(
+            direction,
+            self.getActiveSurface(),
+            .none,
+        ) catch |err| {
+            log.warn("new split failed error={}", .{err});
+        };
+    }
+
+    pub fn actionEqualize(
+        _: *gio.SimpleAction,
+        parameter_: ?*glib.Variant,
+        self: *Self,
+    ) callconv(.c) void {
+        _ = parameter_;
+
+        const old_tree = self.getTree() orelse return;
+        var new_tree = old_tree.equalize(Application.default().allocator()) catch |err| {
+            log.warn("unable to equalize tree: {}", .{err});
+            return;
+        };
+        defer new_tree.deinit();
+        self.setTree(&new_tree);
+    }
+
+    pub fn actionZoom(
+        _: *gio.SimpleAction,
+        _: ?*glib.Variant,
+        self: *Self,
+    ) callconv(.c) void {
+        const tree = self.getTree() orelse return;
+        if (tree.zoomed != null) {
+            tree.zoomed = null;
+        } else {
+            const active = self.getActiveSurfaceHandle() orelse return;
+            if (tree.zoomed == active) return;
+            tree.zoom(active);
+        }
+
+        self.as(gobject.Object).notifyByPspec(properties.tree.impl.param_spec);
+    }
+
+    fn surfaceCloseRequest(
+        surface: *Surface,
+        self: *Self,
+    ) callconv(.c) void {
+        const core = surface.core() orelse return;
+
+        // Reset our pending close state
+        const priv = self.private();
+        priv.pending_close = null;
+
+        // Find the surface in the tree to verify this is valid and
+        // set our pending close handle.
+        priv.pending_close = handle: {
+            const tree = self.getTree() orelse return;
+            var it = tree.iterator();
+            while (it.next()) |entry| {
+                if (entry.view == surface) {
+                    break :handle entry.handle;
+                }
+            }
+
+            return;
+        };
+
+        // If we don't need to confirm then just close immediately.
+        if (!core.needsConfirmQuit()) {
+            closeConfirmationClose(
+                null,
+                self,
+            );
+            return;
+        }
+
+        // Show a confirmation dialog
+        const dialog: *CloseConfirmationDialog = .new(.surface);
+        _ = CloseConfirmationDialog.signals.@"close-request".connect(
+            dialog,
+            *Self,
+            closeConfirmationClose,
+            self,
+            .{},
+        );
+        dialog.present(self.as(gtk.Widget));
+    }
+
+    fn closeConfirmationClose(
+        _: ?*CloseConfirmationDialog,
+        self: *Self,
+    ) callconv(.c) void {
+        // Get the handle we're closing
+        const priv = self.private();
+        const handle = priv.pending_close orelse return;
+        priv.pending_close = null;
+
+        // Figure out our next focus target. The next focus target is
+        // always the "previous" surface unless we're the leftmost then
+        // its the next.
+        const old_tree = self.getTree() orelse return;
+        const next_focus: ?*Surface = next_focus: {
+            const alloc = Application.default().allocator();
+            const next_handle: Surface.Tree.Node.Handle =
+                (old_tree.goto(alloc, handle, .previous) catch null) orelse
+                (old_tree.goto(alloc, handle, .next) catch null) orelse
+                break :next_focus null;
+            if (next_handle == handle) break :next_focus null;
+
+            // Note: we don't need to ref this or anything because its
+            // guaranteed to remain in the new tree since its not part
+            // of the handle we're removing.
+            break :next_focus old_tree.nodes[next_handle.idx()].leaf;
+        };
+
+        // Remove it from the tree.
+        var new_tree = old_tree.remove(
+            Application.default().allocator(),
+            handle,
+        ) catch |err| {
+            log.warn("unable to remove surface from tree: {}", .{err});
+            return;
+        };
+        defer new_tree.deinit();
+        self.setTree(&new_tree);
+
+        // Grab focus. We have to set this on the "last focused" because our
+        // focus will be set when the tree is redrawn.
+        if (next_focus) |v| priv.last_focused.set(v);
+    }
+
+    fn propSurfaceFocused(
+        surface: *Surface,
+        _: *gobject.ParamSpec,
+        self: *Self,
+    ) callconv(.c) void {
+        // We never CLEAR our last_focused because the property is specifically
+        // the last focused surface. We let the weakref clear itself when
+        // the surface is destroyed.
+        if (!surface.getFocused()) return;
+        self.private().last_focused.set(surface);
+
+        // Our active surface probably changed
+        self.as(gobject.Object).notifyByPspec(properties.@"active-surface".impl.param_spec);
+    }
+
+    fn propTree(
+        self: *Self,
+        _: *gobject.ParamSpec,
+        _: ?*anyopaque,
+    ) callconv(.c) void {
+        const priv = self.private();
+
+        // No matter what we notify
+        self.as(gobject.Object).freezeNotify();
+        defer self.as(gobject.Object).thawNotify();
+        self.as(gobject.Object).notifyByPspec(properties.@"has-surfaces".impl.param_spec);
+        self.as(gobject.Object).notifyByPspec(properties.@"is-zoomed".impl.param_spec);
+
+        // If we were planning a rebuild, always remove that so we can
+        // start from a clean slate.
+        if (priv.rebuild_source) |v| {
+            if (glib.Source.remove(v) == 0) {
+                log.warn("unable to remove rebuild source", .{});
+            }
+            priv.rebuild_source = null;
+        }
+
+        // If we transitioned to an empty tree, clear immediately instead of
+        // waiting for an idle callback. Delaying teardown can keep the last
+        // surface alive during shutdown if the main loop exits first.
+        if (priv.tree == null) {
+            priv.tree_bin.setChild(null);
+            return;
+        }
+
+        // Build on an idle callback so rapid tree changes are debounced.
+        // We keep the existing tree attached until the rebuild runs,
+        // which avoids transient empty frames.
+        assert(priv.rebuild_source == null);
+        priv.rebuild_source = glib.idleAdd(
+            onRebuild,
+            self,
+        );
+    }
+
+    fn onRebuild(ud: ?*anyopaque) callconv(.c) c_int {
+        const self: *Self = @ptrCast(@alignCast(ud orelse return 0));
+
+        // Always mark our rebuild source as null since we're done.
+        const priv = self.private();
+        priv.rebuild_source = null;
+
+        // Rebuild our tree
+        const tree: *const Surface.Tree = self.private().tree orelse &.empty;
+        if (tree.isEmpty()) {
+            priv.tree_bin.setChild(null);
+        } else {
+            const built = self.buildTree(
+                tree,
+                tree.zoomed orelse .root,
+            );
+            defer built.deinit();
+            priv.tree_bin.setChild(built.widget);
+        }
+
+        // Replacing our tree widget hierarchy can reset focus state.
+        // If we have a last-focused surface, restore focus to it.
+        if (priv.last_focused.get()) |v| {
+            defer v.unref();
+            v.grabFocus();
+        }
+
+        // Our split status may have changed
+        self.as(gobject.Object).notifyByPspec(properties.@"is-split".impl.param_spec);
+
+        // Our active surface may have changed
+        self.as(gobject.Object).notifyByPspec(properties.@"active-surface".impl.param_spec);
+
+        return 0;
+    }
+
+    /// Builds the widget tree associated with a surface split tree.
+    ///
+    /// Returned widgets are expected to be attached to a parent by the caller.
+    ///
+    /// If `release_ref` is true then `widget` has an extra temporary
+    /// reference that must be released once it is parented in the rebuilt
+    /// tree.
+    const BuildTreeResult = struct {
+        widget: *gtk.Widget,
+        release_ref: bool,
+
+        pub fn initNew(widget: *gtk.Widget) BuildTreeResult {
+            return .{ .widget = widget, .release_ref = false };
+        }
+
+        pub fn initReused(widget: *gtk.Widget) BuildTreeResult {
+            // We add a temporary ref to the widget to ensure it doesn't
+            // get destroyed while we're rebuilding the tree and detaching
+            // it from its old parent. The caller is expected to release
+            // this ref once the widget is attached to its new parent.
+            _ = widget.as(gobject.Object).ref();
+
+            // Detach after we ref it so that this doesn't mark the
+            // widget for destruction.
+            detachWidget(widget);
+
+            return .{ .widget = widget, .release_ref = true };
+        }
+
+        pub fn deinit(self: BuildTreeResult) void {
+            // If we have to release a ref, do it.
+            if (self.release_ref) self.widget.as(gobject.Object).unref();
+        }
+    };
+
+    fn buildTree(
+        self: *Self,
+        tree: *const Surface.Tree,
+        current: Surface.Tree.Node.Handle,
+    ) BuildTreeResult {
+        return switch (tree.nodes[current.idx()]) {
+            .leaf => |v| leaf: {
+                const window = ext.getAncestor(
+                    SurfaceScrolledWindow,
+                    v.as(gtk.Widget),
+                ) orelse {
+                    // The surface isn't in a window already so we don't
+                    // have to worry about reuse.
+                    break :leaf .initNew(gobject.ext.newInstance(
+                        SurfaceScrolledWindow,
+                        .{ .surface = v },
+                    ).as(gtk.Widget));
+                };
+
+                // Keep this widget alive while we detach it from the
+                // old tree and adopt it into the new one.
+                break :leaf .initReused(window.as(gtk.Widget));
+            },
+            .split => |s| split: {
+                const left = self.buildTree(tree, s.left);
+                defer left.deinit();
+                const right = self.buildTree(tree, s.right);
+                defer right.deinit();
+
+                break :split .initNew(SplitTreeSplit.new(
+                    current,
+                    &s,
+                    left.widget,
+                    right.widget,
+                ).as(gtk.Widget));
+            },
+        };
+    }
+
+    /// Detach a split widget from its current parent.
+    ///
+    /// We intentionally use parent-specific child APIs when possible
+    /// (`GtkPaned.setStartChild/setEndChild`, `AdwBin.setChild`) instead of
+    /// calling `gtk.Widget.unparent` directly. Container implementations track
+    /// child pointers/properties internally, and those setters are the path
+    /// that keeps container state and notifications in sync.
+    fn detachWidget(widget: *gtk.Widget) void {
+        const parent = widget.getParent() orelse return;
+
+        // Surface will be in a paned when it is split.
+        if (gobject.ext.cast(gtk.Paned, parent)) |paned| {
+            if (paned.getStartChild()) |child| {
+                if (child == widget) {
+                    paned.setStartChild(null);
+                    return;
+                }
+            }
+
+            if (paned.getEndChild()) |child| {
+                if (child == widget) {
+                    paned.setEndChild(null);
+                    return;
+                }
+            }
+        }
+
+        // Surface will be in a bin when it is not split.
+        if (gobject.ext.cast(adw.Bin, parent)) |bin| {
+            if (bin.getChild()) |child| {
+                if (child == widget) {
+                    bin.setChild(null);
+                    return;
+                }
+            }
+        }
+
+        // Fallback for unexpected parents where we don't have a typed
+        // container API available.
+        widget.unparent();
+    }
+
+    //---------------------------------------------------------------
+    // Class
+
+    const C = Common(Self, Private);
+    pub const as = C.as;
+    pub const ref = C.ref;
+    pub const unref = C.unref;
+    const private = C.private;
+
+    pub const Class = extern struct {
+        parent_class: Parent.Class,
+        var parent: *Parent.Class = undefined;
+        pub const Instance = Self;
+
+        fn init(class: *Class) callconv(.c) void {
+            gobject.ext.ensureType(Surface);
+            gtk.Widget.Class.setTemplateFromResource(
+                class.as(gtk.Widget.Class),
+                comptime gresource.blueprint(.{
+                    .major = 1,
+                    .minor = 5,
+                    .name = "split-tree",
+                }),
+            );
+
+            // Properties
+            gobject.ext.registerProperties(class, &.{
+                properties.@"active-surface".impl,
+                properties.@"has-surfaces".impl,
+                properties.@"is-zoomed".impl,
+                properties.tree.impl,
+                properties.@"is-split".impl,
+            });
+
+            // Bindings
+            class.bindTemplateChildPrivate("tree_bin", .{});
+
+            // Template Callbacks
+            class.bindTemplateCallback("notify_tree", &propTree);
+
+            // Signals
+            signals.changed.impl.register(.{});
+
+            // Virtual methods
+            gobject.Object.virtual_methods.dispose.implement(class, &dispose);
+            gobject.Object.virtual_methods.finalize.implement(class, &finalize);
+        }
+
+        pub const as = C.Class.as;
+        pub const bindTemplateChildPrivate = C.Class.bindTemplateChildPrivate;
+        pub const bindTemplateCallback = C.Class.bindTemplateCallback;
+    };
+};
+
+/// This is an internal-only widget that represents a split in the
+/// split tree. This is a wrapper around gtk.Paned that allows us to handle
+/// ratio (0 to 1) based positioning of the split, and also allows us to
+/// write back the updated ratio to the split tree when the user manually
+/// adjusts the split position.
+///
+/// Since this is internal, it expects to be nested within a SplitTree and
+/// will use `getAncestor` to find the SplitTree it belongs to.
+///
+/// This is an _immutable_ widget. It isn't meant to be updated after
+/// creation. As such, there are no properties or APIs to change the split,
+/// access the paned, etc.
+const SplitTreeSplit = extern struct {
+    const Self = @This();
+    parent_instance: Parent,
+    pub const Parent = adw.Bin;
+    pub const getGObjectType = gobject.ext.defineClass(Self, .{
+        .name = "GhosttySplitTreeSplit",
+        .instanceInit = &init,
+        .classInit = &Class.init,
+        .parent_class = &Class.parent,
+        .private = .{ .Type = Private, .offset = &Private.offset },
+    });
+
+    const Private = struct {
+        /// The handle of the node in the tree that this split represents.
+        /// Assumed to be correct.
+        handle: Surface.Tree.Node.Handle,
+
+        /// Source to handle repositioning the split when properties change.
+        idle: ?c_uint = null,
+
+        // Template bindings
+        paned: *gtk.Paned,
+
+        pub var offset: c_int = 0;
+    };
+
+    /// Create a new split.
+    ///
+    /// The reason we don't use GObject properties here is because this is
+    /// an immutable widget and we don't want to deal with the overhead of
+    /// all the boilerplate for properties, signals, bindings, etc.
+    pub fn new(
+        handle: Surface.Tree.Node.Handle,
+        split: *const Surface.Tree.Split,
+        start_child: *gtk.Widget,
+        end_child: *gtk.Widget,
+    ) *Self {
+        const self = gobject.ext.newInstance(Self, .{});
+        const priv = self.private();
+        priv.handle = handle;
+
+        // Setup our paned fields
+        const paned = priv.paned;
+        paned.setStartChild(start_child);
+        paned.setEndChild(end_child);
+        paned.as(gtk.Orientable).setOrientation(switch (split.layout) {
+            .horizontal => .horizontal,
+            .vertical => .vertical,
+        });
+
+        // Signals and so on are setup in the template.
+
+        return self;
+    }
+
+    fn init(self: *Self, _: *Class) callconv(.c) void {
+        gtk.Widget.initTemplate(self.as(gtk.Widget));
+    }
+
+    fn refresh(self: *Self) void {
+        const priv = self.private();
+        if (priv.idle == null) priv.idle = glib.idleAdd(
+            onIdle,
+            self,
+        );
+    }
+
+    fn onIdle(ud: ?*anyopaque) callconv(.c) c_int {
+        const self: *Self = @ptrCast(@alignCast(ud orelse return 0));
+        const priv = self.private();
+        const paned = priv.paned;
+
+        // Our idle source is always over
+        priv.idle = null;
+
+        // Get our split. This is the most dangerous part of this entire
+        // widget. We assume that this widget is always a child of a
+        // SplitTree, we assume that our handle is valid, and we assume
+        // the handle is always a split node.
+        const split_tree = ext.getAncestor(
+            SplitTree,
+            self.as(gtk.Widget),
+        ) orelse return 0;
+        const tree = split_tree.getTree() orelse return 0;
+        const split: *const Surface.Tree.Split = &tree.nodes[priv.handle.idx()].split;
+
+        // Current, min, and max positions as pixels.
+        const pos = paned.getPosition();
+        const min = min: {
+            var val = gobject.ext.Value.new(c_int);
+            defer val.unset();
+            gobject.Object.getProperty(
+                paned.as(gobject.Object),
+                "min-position",
+                &val,
+            );
+            break :min gobject.ext.Value.get(&val, c_int);
+        };
+        const max = max: {
+            var val = gobject.ext.Value.new(c_int);
+            defer val.unset();
+            gobject.Object.getProperty(
+                paned.as(gobject.Object),
+                "max-position",
+                &val,
+            );
+            break :max gobject.ext.Value.get(&val, c_int);
+        };
+        const pos_set: bool = max: {
+            var val = gobject.ext.Value.new(c_int);
+            defer val.unset();
+            gobject.Object.getProperty(
+                paned.as(gobject.Object),
+                "position-set",
+                &val,
+            );
+            break :max gobject.ext.Value.get(&val, c_int) != 0;
+        };
+
+        // We don't actually use min, but we don't expect this to ever
+        // be non-zero, so let's add an assert to ensure that.
+        assert(min == 0);
+
+        // If our max is zero then we can't do any math. I don't know
+        // if this is possible but I suspect it can be if you make a nested
+        // split completely minimized.
+        if (max == 0) return 0;
+
+        // Determine our current ratio.
+        const current_ratio: f64 = ratio: {
+            const pos_f64: f64 = @floatFromInt(pos);
+            const max_f64: f64 = @floatFromInt(max);
+            break :ratio pos_f64 / max_f64;
+        };
+        const desired_ratio: f64 = @floatCast(split.ratio);
+
+        // If our ratio is close enough to our desired ratio, then
+        // we ignore the update. This is to avoid constant split updates
+        // for lossy floating point math.
+        if (std.math.approxEqAbs(
+            f64,
+            current_ratio,
+            desired_ratio,
+            0.001,
+        )) {
+            return 0;
+        }
+
+        // If we're out of bounds, then we need to either set the position
+        // to what we expect OR update our expected ratio.
+
+        // If we've never set the position, then we set it to the desired.
+        if (!pos_set) {
+            const desired_pos: c_int = desired_pos: {
+                const max_f64: f64 = @floatFromInt(max);
+                break :desired_pos @intFromFloat(@round(max_f64 * desired_ratio));
+            };
+            paned.setPosition(desired_pos);
+            return 0;
+        }
+
+        // If we've set the position, then this is a manual human update
+        // and we need to write our update back to the tree.
+        tree.resizeInPlace(priv.handle, @floatCast(current_ratio));
+
+        return 0;
+    }
+
+    //---------------------------------------------------------------
+    // Signal handlers
+
+    fn propPosition(
+        _: *gtk.Paned,
+        _: *gobject.ParamSpec,
+        self: *Self,
+    ) callconv(.c) void {
+        self.refresh();
+    }
+
+    fn propMaxPosition(
+        _: *gtk.Paned,
+        _: *gobject.ParamSpec,
+        self: *Self,
+    ) callconv(.c) void {
+        self.refresh();
+    }
+
+    fn propMinPosition(
+        _: *gtk.Paned,
+        _: *gobject.ParamSpec,
+        self: *Self,
+    ) callconv(.c) void {
+        self.refresh();
+    }
+
+    //---------------------------------------------------------------
+    // Virtual methods
+
+    fn dispose(self: *Self) callconv(.c) void {
+        const priv = self.private();
+        if (priv.idle) |v| {
+            if (glib.Source.remove(v) == 0) {
+                log.warn("unable to remove idle source", .{});
+            }
+            priv.idle = null;
+        }
+
+        gtk.Widget.disposeTemplate(
+            self.as(gtk.Widget),
+            getGObjectType(),
+        );
+
+        gobject.Object.virtual_methods.dispose.call(
+            Class.parent,
+            self.as(Parent),
+        );
+    }
+
+    fn finalize(self: *Self) callconv(.c) void {
+        gobject.Object.virtual_methods.finalize.call(
+            Class.parent,
+            self.as(Parent),
+        );
+    }
+
+    const C = Common(Self, Private);
+    pub const as = C.as;
+    pub const ref = C.ref;
+    pub const unref = C.unref;
+    const private = C.private;
+
+    pub const Class = extern struct {
+        parent_class: Parent.Class,
+        var parent: *Parent.Class = undefined;
+        pub const Instance = Self;
+
+        fn init(class: *Class) callconv(.c) void {
+            gtk.Widget.Class.setTemplateFromResource(
+                class.as(gtk.Widget.Class),
+                comptime gresource.blueprint(.{
+                    .major = 1,
+                    .minor = 5,
+                    .name = "split-tree-split",
+                }),
+            );
+
+            // Bindings
+            class.bindTemplateChildPrivate("paned", .{});
+
+            // Template Callbacks
+            class.bindTemplateCallback("notify_max_position", &propMaxPosition);
+            class.bindTemplateCallback("notify_min_position", &propMinPosition);
+            class.bindTemplateCallback("notify_position", &propPosition);
+
+            // Virtual methods
+            gobject.Object.virtual_methods.dispose.implement(class, &dispose);
+            gobject.Object.virtual_methods.finalize.implement(class, &finalize);
+        }
+
+        pub const as = C.Class.as;
+        pub const bindTemplateChildPrivate = C.Class.bindTemplateChildPrivate;
+        pub const bindTemplateCallback = C.Class.bindTemplateCallback;
+    };
+};