output: add output_title default option

Outputs now have a default option, "output_title". If this changes, the
outputs title is set to the option value. This title is currently only
relevant when run nested in a wayland/X11 session.

Co-authored-by: Isaac Freund <ifreund@ifreund.xyz>

river/Option.zig

@@ -45,6 +45,9 @@ output: ?*Output,
 key: [*:0]const u8,
 value: Value = .unset,
 
+/// Emitted whenever the value of the option changes.
+update: wl.Signal(*Self) = undefined,
+
 handles: wl.list.Head(zriver.OptionHandleV1, null) = undefined,
 
 pub fn create(options_manager: *OptionsManager, output: ?*Output, key: [*:0]const u8) !*Self {
@@ -57,6 +60,7 @@ pub fn create(options_manager: *OptionsManager, output: ?*Output, key: [*:0]cons
         .key = try util.gpa.dupeZ(u8, mem.span(key)),
     };
     self.handles.init();
+    self.update.init();
 
     options_manager.options.append(self);
 
@@ -101,6 +105,9 @@ pub fn set(self: *Self, value: Value) !void {
 
     var it = self.handles.iterator(.forward);
     while (it.next()) |handle| self.sendValue(handle);
+
+    // Call listeners, if any.
+    self.update.emit(self);
 }
 
 fn sendValue(self: Self, handle: *zriver.OptionHandleV1) void {

river/Output.zig

@@ -18,6 +18,8 @@
 const Self = @This();
 
 const std = @import("std");
+const mem = std.mem;
+const fmt = std.fmt;
 const wlr = @import("wlroots");
 const wayland = @import("wayland");
 const wl = wayland.server.wl;
@@ -35,6 +37,7 @@ const View = @import("View.zig");
 const ViewStack = @import("view_stack.zig").ViewStack;
 const AttachMode = @import("view_stack.zig").AttachMode;
 const OutputStatus = @import("OutputStatus.zig");
+const Option = @import("Option.zig");
 
 const State = struct {
     /// A bit field of focused tags
@@ -84,6 +87,9 @@ enable: wl.Listener(*wlr.Output) = wl.Listener(*wlr.Output).init(handleEnable),
 frame: wl.Listener(*wlr.Output) = wl.Listener(*wlr.Output).init(handleFrame),
 mode: wl.Listener(*wlr.Output) = wl.Listener(*wlr.Output).init(handleMode),
 
+// Listeners for options
+output_title: wl.Listener(*Option) = wl.Listener(*Option).init(handleTitleChange),
+
 pub fn init(self: *Self, root: *Root, wlr_output: *wlr.Output) !void {
     // Some backends don't have modes. DRM+KMS does, and we need to set a mode
     // before we can use the output. The mode is a tuple of (width, height,
@@ -138,6 +144,10 @@ pub fn init(self: *Self, root: *Root, wlr_output: *wlr.Output) !void {
             .height = effective_resolution.height,
         };
     }
+
+    var buf: ["river - ".len + wlr_output.name.len + 1]u8 = undefined;
+    const default_title = fmt.bufPrintZ(&buf, "river - {}", .{mem.spanZ(&wlr_output.name)}) catch unreachable;
+    try self.defaultOption("output_title", .{ .string = default_title.ptr }, &self.output_title);
 }
 
 pub fn getLayer(self: *Self, layer: zwlr.LayerShellV1.Layer) *std.TailQueue(LayerSurface) {
@@ -545,3 +555,29 @@ pub fn getEffectiveResolution(self: *Self) struct { width: u32, height: u32 } {
         .height = @intCast(u32, height),
     };
 }
+
+pub fn setTitle(self: *Self, title: [*:0]const u8) void {
+    if (self.wlr_output.isWl()) {
+        self.wlr_output.wlSetTitle(title);
+    } else if (self.wlr_output.isX11()) {
+        self.wlr_output.x11SetTitle(title);
+    }
+}
+
+/// Create an option for this output, attach a listener which is called when
+/// the option changed and initialize with a default value. Note that the
+/// listener is called once through this function.
+fn defaultOption(
+    self: *Self,
+    key: [*:0]const u8,
+    value: Option.Value,
+    listener: *wl.Listener(*Option),
+) !void {
+    const option = try Option.create(&self.root.server.options_manager, self, key);
+    option.update.add(listener);
+    try option.set(value);
+}
+
+fn handleTitleChange(listener: *wl.Listener(*Option), option: *Option) void {
+    if (option.value.string) |title| option.output.?.setTitle(title);
+}

river/Server.zig

@@ -112,12 +112,12 @@ pub fn init(self: *Self) !void {
 
     self.config = try Config.init();
     try self.decoration_manager.init(self);
+    try self.options_manager.init(self);
     try self.root.init(self);
     // Must be called after root is initialized
     try self.input_manager.init(self);
     try self.control.init(self);
     try self.status_manager.init(self);
-    try self.options_manager.init(self);
 
     // These all free themselves when the wl_server is destroyed
     _ = try wlr.DataDeviceManager.create(self.wl_server);