fix(policy): 新增窗口后通知原焦点窗口状态变更

新增 window_get_showing_title，按 title → instance_name →
class_name → app_id 优先级取显示标题，窗口快照改用该函数，
避免标题缺失时显示为空。

.clangd

@@ -2,3 +2,4 @@
 
 Completion:
   ArgumentLists: None
+  HeaderInsertion: Never

CMakeLists.txt

@@ -29,12 +29,14 @@ add_executable(${APP_NAME}
     ${SOURCE_DIR}/backend/x11/common.c
     ${SOURCE_DIR}/backend/x11/cursor.c
     ${SOURCE_DIR}/backend/x11/event.c
+    ${SOURCE_DIR}/backend/x11/tray.c
     ${SOURCE_DIR}/backend/x11/window.c
 
     ${SOURCE_DIR}/bar/bar.c
     ${SOURCE_DIR}/bar/binding.c
     ${SOURCE_DIR}/bar/cell.c
     ${SOURCE_DIR}/bar/text.c
+    ${SOURCE_DIR}/bar/tray.c
     ${SOURCE_DIR}/bar/windows.c
     ${SOURCE_DIR}/bar/workspaces.c
 

Makefile

@@ -1,16 +1,11 @@
 MAKEFILE_ABS_PATH := $(abspath $(lastword $(MAKEFILE_LIST)))
 MAKEFILE_DIR := $(dir $(MAKEFILE_ABS_PATH))
-PWD_DIR := $(CURDIR)/
 BUILD_DIR := $(addprefix $(MAKEFILE_DIR),build)
 SRC_DIR := $(addprefix $(MAKEFILE_DIR),/)
 
 TARGET_NAME := zdwm
 TARGET := $(addprefix $(MAKEFILE_DIR),$(TARGET_NAME))
 
-ifneq ($(PWD_DIR),$(MAKEFILE_DIR))
-	TARGET := $(addprefix $(MAKEFILE_DIR),$(TARGET_NAME))
-endif
-
 
 $(TARGET_NAME): build
 
@@ -19,10 +14,10 @@ clean:
 	${RM} -r $(BUILD_DIR)
 
 run:
-	-$(shell Xephyr :3 -screen 1920x1080 -dpi `xrdb -get Xft.dpi` &)
+	Xephyr :3 -screen 1920x1080 -dpi `xrdb -get Xft.dpi`
 
 run_multiple_screen:
-	-$(shell Xephyr :3 -screen 1920x1080 -screen 1920x1080 +xinerama -dpi `xrdb -get Xft.dpi` &)
+	Xephyr :3 -screen 1920x1080 -screen 1920x1080 +xinerama -dpi `xrdb -get Xft.dpi`
 
 wm: $(TARGET_NAME)
 	DISPLAY=:3 $(TARGET)

docs/tray-design.org

@@ -42,7 +42,7 @@ X11 系统托盘协议只要求：tray 创建一个 window 成为 =_NET_SYSTEM_T
 
 * 后端接口设计
 
-tray 契约独立成头 =src/bar/tray.h= —— *不放 core*，因为 tray 与 core 无关（core 不感知 tray）。由 bar 定义、后端实现（消费方定义接口、提供方实现的依赖倒置；契约是纯抽象头）。它只依赖 =core/types.h=（=window_id_t=），不含 =backend_t=，所以 bar include 它而不碰 =core/backend.h=，保持"bar 不知道后端内部"。=core/backend.h= 反过来 include =bar/tray.h=，让 =backend_bar_window_t= 内嵌 =tray_t=。
+tray 契约独立成头 =interface/tray.h= —— 落 interface 层：不放 core（tray 与 core 无关），也不放 bar（backend 也要实现它）。bar 和 backend 作为两个对等实现层，都依赖 =interface/tray.h= 来解耦——这正是分层消除 bar↔backend 交叉依赖的落点（详见 [[file:module-layering.org][module-layering.org]] 的 tray 落点）。它只依赖 =interface/types.h=（=window_id_t=），不含 =backend_t=，所以 bar include 它而不碰 =interface/backend.h= 的内部。=interface/backend.h= 反过来 include =interface/tray.h=，让 =backend_bar_window_t= 内嵌 =tray_t=。
 
 #+begin_src c
 typedef void (*tray_icons_change_cb_t)(void *user_data);
@@ -233,20 +233,20 @@ bar 重绘是 timerfd（fps）驱动，非事件驱动。tray icon 是真实窗
 
 * 关键文件清单
 
-| 文件                         | 改动                                                                                                     |
-|------------------------------+----------------------------------------------------------------------------------------------------------|
-| =src/bar/tray.h=             | **新增** tray 契约：=tray_t= / =tray_api_t= / =tray_icons_change_cb_t=（bar 定义、后端实现；不进 core） |
-| =src/core/backend.h=         | include =bar/tray.h=；=backend_bar_window_t= 内嵌 =tray_t=；扩展 =backend_create_bar_window=（加 =enable_tray=） |
-| =src/backend/x11/tray.c=     | *新增*：selection / MANAGER / 基础 XEMBED / icon 管理 / =place=                                          |
-| =src/backend/x11/internal.h= | =ATOM_LIST= 追加 tray/XEMBED atoms；=backend_t= 加 =tray= 字段                                           |
-| =src/backend/x11/event.c=    | 消化 tray 相关 client message（不产 =event_t=）                                                          |
-| =src/backend/x11/backend.c=  | =backend_create_bar_window= 实现 enable_tray 分支；=backend_destroy= 释放 tray                           |
-| =src/bar/types.h=            | =bar_cell_t= 加 =fixed_width=；=bar_t= 加 =tray=                                                         |
-| =src/bar/cell.h= / =cell.c=  | =cell_api= 加 =cell_set_fixed_width= / =cell_get_region=                                                 |
-| =src/bar/bar.c=              | layout 支持 =fixed_width=；=bar_draw= 调 after 钩子；=bar_init= 加 tray item；新增 layout params 类型    |
-| =src/bar/tray.c=             | *新增*：tray item 实现                                                                                   |
-| =src/runtime/runtime.c=      | =runtime_init_bar= 传 =enable_tray=、存 =bar->tray=                                                      |
-| =include/zdwm/config.h=      | =zdwm_bar_config_t= 加 =tray_output_index=                                                               |
+| 文件                         | 改动                                                                                                                   |
+|------------------------------+------------------------------------------------------------------------------------------------------------------------|
+| =interface/tray.h=           | **新增** tray 契约：=tray_t= / =tray_api_t= / =tray_icons_change_cb_t=（bar 与 backend 共享，落 interface 解耦）       |
+| =interface/backend.h=        | include =interface/tray.h=；=backend_bar_window_t= 内嵌 =tray_t=；扩展 =backend_create_bar_window=（加 =enable_tray=） |
+| =src/backend/x11/tray.c=     | *新增*：selection / MANAGER / 基础 XEMBED / icon 管理 / =place=                                                        |
+| =src/backend/x11/internal.h= | =ATOM_LIST= 追加 tray/XEMBED atoms；=backend_t= 加 =tray= 字段                                                         |
+| =src/backend/x11/event.c=    | 消化 tray 相关 client message（不产 =event_t=）                                                                        |
+| =src/backend/x11/backend.c=  | =backend_create_bar_window= 实现 enable_tray 分支；=backend_destroy= 释放 tray                                         |
+| =src/bar/types.h=            | =bar_cell_t= 加 =fixed_width=；=bar_t= 加 =tray=                                                                       |
+| =src/bar/cell.h= / =cell.c=  | =cell_api= 加 =cell_set_fixed_width= / =cell_get_region=                                                               |
+| =src/bar/bar.c=              | layout 支持 =fixed_width=；=bar_draw= 调 after 钩子；=bar_init= 加 tray item；新增 layout params 类型                  |
+| =src/bar/tray.c=             | *新增*：tray item 实现                                                                                                 |
+| =src/runtime/runtime.c=      | =runtime_init_bar= 传 =enable_tray=、存 =bar->tray=                                                                    |
+| =include/zdwm/config.h=      | =zdwm_bar_config_t= 加 =tray_output_index=                                                                             |
 
 * 复用现有
 

docs/tray-implementation-plan.org

@@ -0,0 +1,91 @@
+#+title: ZDWM Tray 系统托盘实现计划
+#+OPTIONS: toc:2
+
+* 背景
+
+bar 当前没有系统托盘。目标是让外部应用（输入法、音量、蓝牙、网络等）的 tray icon 显示在 bar 右侧并正常交互。
+
+设计文档 [[file:tray-design.org][tray-design.org]] 已把方案定死。刚完成的模块分层重构（[[file:module-layering.org][module-layering.org]]）为 tray 铺了路——=interface/= 层让 bar 与 backend 经契约解耦，tray 契约落 =interface/tray.h= 消除 =bar↔backend= 交叉依赖（分层的核心动机之一）。
+
+* 关键决策
+
+- *契约落 =interface/tray.h=*（分层后的位置，非设计文档旧版的 =src/bar/tray.h=）。
+- *tray 闭环后端*：core 的 =event_t= / =policy= / =plan= 完全不感知；tray 消息在 =event.c= 拦截后 =return false=，不进 policy 路由。
+- *tray 是 bar 附属 + 后端单例*：生命周期随 bar 窗口；=_NET_SYSTEM_TRAY_S0= selection owner 全 display 唯一，挂到最后一个 =enable_tray=true= 的 output。
+- *第一版范围*：selection owner + MANAGER 广播 + 基础 XEMBED（reparent + =_XEMBED_EMBEDDED_NOTIFY=）+ icon 显示与点击 + icon 尺寸 = bar 高度（不缩放）。焦点/激活转发、尺寸协商、客户端异常断开清理放后续迭代。
+- *tray 存 =bar_t.tray=（一份）*：单例语义，=bar_init= 时用 =host_window()= 匹配决定哪个 output 渲染。
+
+* 实现步骤
+
+每步可独立编译，建议每步一个提交。
+
+** 步骤 1：契约层 + 调用点占位
+
+签名变更与唯一调用点耦合，必须一起改才能编译。
+
+- *新增 =src/interface/tray.h=*（纯声明，零 .c）：=tray_icons_change_cb_t=、=tray_api_t=（=host_window= / =icon_count= / =icon_size= / =place= / =set_listener=）、=tray_t=（=api= + =handle=）。只依赖 =interface/types.h=。
+- *=src/interface/backend.h=*：=#include "interface/tray.h"=；=backend_bar_window_t= 内嵌 =tray_t tray=；=backend_create_bar_window= 加 =bool enable_tray=。
+- *=src/runtime/runtime.c=*：临时传 =enable_tray=false=。
+- *=src/backend/x11/backend.c=*：签名加参数，函数体先忽略，返回 =.tray = {0}=。
+- 验证：编译通过，bar 行为不变。
+
+** 步骤 2：bar 框架扩展（零影响现有 3 个 item）
+
+为 tray item 铺路；钩子可空、=fixed_width= 默认 0，现有 item 走原路径。
+
+- *=include/zdwm/bar.h=*：=zdwm_bar_item_type_t= 加可空钩子 =after_layout= / =after_draw=；新增 =zdwm_bar_item_layout_params_t=（仿 =zdwm_bar_click_params_t=：=item= / =cell_api= / =region= / =state=）；=zdwm_bar_cell_api_t= 加 =cell_set_fixed_width=、=cell_get_region=。
+- *=src/bar/types.h=*：=bar_cell_t= 加 =int32_t fixed_width=（默认 0 = 走文本测量，=p_clear= 后天然正确；<0 = 隐藏哨兵）。
+- *=src/bar/cell.c=*：实现 =bar_cell_set_fixed_width= / =bar_cell_get_region=，注册进 =bar_cell_api=。
+- *=src/bar/bar.c=*：=bar_output_layout= 三处宽度计算加 =fixed_width= 分支（>0 固定 / ==0 测量 / <0 隐藏）；=bar_draw= 在 layout 后遍历调 =after_layout=、draw 后调 =after_draw=（NULL 跳过）。
+- 验证：编译 + 运行，*workspaces/binding/windows 三个 item 视觉与点击零变化*（关键回归点）。
+
+** 步骤 3：后端协议层（核心）
+
+tray 能力全部 X11 细节，"已实现但未启用"。
+
+- *新增 =src/backend/x11/tray.c=*：tray host 状态 + 成为 =_NET_SYSTEM_TRAY_S0= owner + 广播 MANAGER + 容器子窗口（reparent 到当前 bar）+ 基础 XEMBED（reparent icon + =_XEMBED_EMBEDDED_NOTIFY=）+ dock 请求处理 + =place(handle,x)=（move 容器、configure 每个 icon 到 =x + i*icon_size=）+ 填充 =static const tray_api_t=（=handle= 实际是 =backend_t*=）。=icon_size= 用 bar 窗口高度（单一数据源）。
+- *=src/backend/x11/internal.h=*：=ATOM_LIST= 追加 =_NET_SYSTEM_TRAY_S0= / =_NET_SYSTEM_TRAY_OPCODE= / =_NET_SYSTEM_TRAY_MESSAGE_DATA= / =_XEMBED= / =_XEMBED_INFO= / =Manager=；=backend_t= 加 tray host 字段（单例：host_window、icon 列表、listener、enabled）。
+- *=src/backend/x11/event.c=*（=handle_client_message=）：开头拦截 tray 消息（=Manager= 且 =data.data32[1]==_NET_SYSTEM_TRAY_S0=；=_NET_SYSTEM_TRAY_OPCODE= 的 =REQUEST_DOCK=），处理后 =return false=（不产 =event_t=）。
+- *=src/backend/x11/backend.c=*：=backend_create_bar_window= 的 =enable_tray=true= 分支（创建/迁移 host 容器到此 bar 窗口，返回 =tray= 填 backend 的 api + =handle=backend=）；=backend_destroy= 释放 tray（selection、容器、icon 列表）。
+- *=CMakeLists.txt=*：加 =src/backend/x11/tray.c=。
+- 验证：编译通过。runtime 仍传 false，行为不变。
+
+** 步骤 4：bar tray item
+
+消费步骤 2 的框架 + 步骤 3 的契约，tray 作为 right-side item 接入。
+
+- *新增 =src/bar/tray.c=*（参考 =workspaces.c= 模式）：=bar_tray= vtable = =create_state= / =update= / =on_click= / =after_layout= / =destroy_state=。=create_state= 拷贝 =tray_t= + =set_listener= 注册回调（置 dirty）；=update= 在 dirty 时 =set_cell_count(icon_count)= + 循环 =cell_set_fixed_width(i, icon_size)=；=on_click= 返回 =ACTION_NONE=（icon 真实子窗口自收点击）；=after_layout= 调 =place(handle, region.start)=。cell 不画 cairo（text 空，被真实 icon 窗口盖住）。
+- *=src/bar/bar.h=*：=bar_t= 加 =tray_t tray=（一份，单例）。
+- *=src/bar/bar.c=*（=bar_init=）：遍历 output，对 =bar->tray.host_window()= 匹配自身 =window_id= 的 output 调 =bar_output_add_tray=（right side），其余不加。
+- *=CMakeLists.txt=*：加 =src/bar/tray.c=。
+- 验证：编译通过。right side 仍空（runtime 未注入 tray）。
+
+** 步骤 5：runtime/配置串起来（启用）
+
+- *=include/zdwm/bar.h=*（=zdwm_bar_config_t=）：加 =int32_t tray_output_index=（默认 0 = 第一个 output）。
+- *=src/runtime/runtime.c=*（=runtime_init_bar=）：=bool enable_tray = ((int32_t)i == runtime->bar.config.tray_output_index);= 传给 =backend_create_bar_window=；=runtime->bar.tray = bar_window.tray;=（每个返回都一样，存一份）。
+- *=src/config/defaults.c=*：=tray_output_index= 默认 0。
+- 验证：编译 + 运行，tray 启用。
+
+* 风险点
+
+- *after 钩子对现有 item*：现有三个 item 的 vtable 不显式初始化新钩子 → NULL（C 部分初始化保证）；=bar_draw= 调用前判 NULL。=fixed_width= 默认 0 走原测量路径。步骤 2 后必须确认三个 item 零变化。
+- *selection owner 单例 vs per-output create*：host 是 backend 单例；每次 =enable_tray=true= 把容器 reparent 到本次 bar 窗口，最终挂最后一个 true 的 output；=host_window()= 返回当前挂载 window_id。
+- *XEMBED 第一版只做基础*：reparent + =EMBEDDED_NOTIFY=；不做焦点/激活/缩放。某些高级 applet（要求焦点的输入法）可能受限，基础音量/网络 icon 无影响。
+- *core 零感知*：tray 消息在 =event.c= 拦截 =return false=，不进 policy/plan。icon 增删不触发 core 重排——icon 是真实 X 子窗口，X server 自管绘制，bar 重绘靠 timerfd 驱动，region 变化经 =after_layout= → =place= 同步。
+- *tray cell padding*：=fixed_width = icon_size=，确保 tray item 的 cell padding 为 0，避免 icon 间额外间距。
+- *透明背景*：bar 窗口已 ARGB（=backend.c= 用 =window_get_visual(true)=），tray 容器子窗口继承，第一版白送。
+
+* 端到端验证
+
+1. *每步编译*：=cmake --build build=，零 warning（项目 =-Wall=）。
+2. *步骤 5 后运行*：=./build/zdwm=。
+3. *tray icon 验证*：启动一个提供 tray icon 的 app（=volumeicon= / =nm-applet= / =fcitx5= 等，不要用 stalonetray——它会抢 selection owner）。验证：icon 显示在 bar *右侧*、尺寸 = bar 高度无溢出、多 icon 横向无重叠、点击有响应、透明背景融入 bar。
+4. *动态增删*：启动/退出 tray app，观察 icon 实时增删 + 布局重排（经 =set_listener= 回调 → dirty → 下个 timerfd tick → =update= 重算 → =after_layout= 重排），无残留空位。
+5. *回归*（每步都做，重点步骤 2）：workspaces tag 切换、binding 模式、windows 标题、bar 点击命中全部不变。
+
+* 关键文件
+
+- *新增*：=src/interface/tray.h=（契约）、=src/backend/x11/tray.c=（协议核心）、=src/bar/tray.c=（bar item）。
+- *修改*：=src/interface/backend.h=、=src/backend/x11/{internal.h,event.c,backend.c}=、=include/zdwm/bar.h=、=src/bar/{types.h,cell.c,bar.c,bar.h}=、=src/runtime/runtime.c=、=src/config/defaults.c=、=CMakeLists.txt=。
+- *复用*：=workspaces.c=（item 模板）、=zdwm_bar_click_params_t=（layout params 打包先例）、=ATOM_LIST= 宏（atom 注册）、=window_get_visual(true)=（ARGB）、=bar_cell_api= vtable 机制。

include/zdwm/bar.h

@@ -39,6 +39,8 @@ typedef struct zdwm_bar_config_t {
   const char *binding_mode_bg;
   const char *binding_mode_fg;
 
+  int32_t tray_output_index;
+
   uint32_t window_padding_x;
   const char *window_bg;
   const char *window_fg;
@@ -48,6 +50,11 @@ typedef struct zdwm_bar_config_t {
 
 typedef struct zdwm_bar_item_t zdwm_bar_item_t;
 
+typedef struct zdwm_bar_x_region_t {
+  int32_t start;
+  int32_t end;
+} zdwm_bar_x_region_t;
+
 typedef struct zdwm_bar_cell_api_t {
   size_t (*get_cell_count)(zdwm_bar_item_t *item);
   void (*set_cell_count)(zdwm_bar_item_t *item, size_t count);
@@ -57,6 +64,13 @@ typedef struct zdwm_bar_cell_api_t {
   void (*cell_set_fg)(zdwm_bar_item_t *item, size_t index, const char *color);
   void (*cell_set_icon)(zdwm_bar_item_t *item, size_t index, zdwm_icon_t icon);
   void (*cell_set_indicator)(zdwm_bar_item_t *item, size_t index, bool show);
+  void (*cell_set_fixed_width)(
+    zdwm_bar_item_t *item,
+    size_t index,
+    int32_t width
+  );
+
+  zdwm_bar_x_region_t (*cell_get_region)(zdwm_bar_item_t *item, size_t index);
 } zdwm_bar_cell_api_t;
 
 typedef struct zdwm_bar_click_params_t {
@@ -68,6 +82,13 @@ typedef struct zdwm_bar_click_params_t {
   void *state;
 } zdwm_bar_click_params_t;
 
+typedef struct zdwm_bar_item_hook_params_t {
+  zdwm_bar_item_t *item;
+  const zdwm_bar_cell_api_t *cell_api;
+  zdwm_bar_x_region_t region;
+  void *state;
+} zdwm_bar_item_hook_params_t;
+
 typedef struct zdwm_bar_item_type_t {
   void *(*create_state)(zdwm_output_id_t output_id, void *config);
   void (*update)(
@@ -75,6 +96,8 @@ typedef struct zdwm_bar_item_type_t {
     const zdwm_bar_cell_api_t *cells,
     void *state
   );
+  void (*after_layout)(const zdwm_bar_item_hook_params_t *params);
+  void (*after_draw)(const zdwm_bar_item_hook_params_t *params);
   zdwm_action_t (*on_click)(zdwm_bar_click_params_t *params);
   void (*destroy_state)(void *state);
   zdwm_bar_item_t *instance;

src/backend/x11/backend.c

@@ -19,6 +19,7 @@
 
 #include "backend/output_utils.h"
 #include "backend/x11/cursor.h"
+#include "backend/x11/tray.h"
 #include "backend/x11/window.h"
 #include "base/app.h"
 #include "base/array.h"
@@ -194,6 +195,8 @@ backend_t *backend_create(const char *display_name) {
 void backend_destroy(backend_t *backend) {
   if (!backend) return;
 
+  tray_cleanup(backend);
+
   p_delete(&backend->config_list.cfgs);
   p_clear(&backend->config_list, 1);
 
@@ -555,6 +558,7 @@ static void backend_merge_effects(
     switch (e->type) {
     case ZDWM_EFFECT_MAP_WINDOW:
       window_list_push(&backend->map, e->as.map.window);
+      window_list_push(&backend->configure, e->as.map.window);
       break;
     case ZDWM_EFFECT_UNMAP_WINDOW:
       window_list_push(&backend->unmap, e->as.unmap.window);
@@ -609,6 +613,9 @@ static void backend_merge_effects(
     case ZDWM_EFFECT_CONFIGURE_WINDOW:
       merge_window_configure_params(backend, &e->as.configure);
       break;
+    case ZDWM_EFFECT_CONFIGURE_NOTIFY:
+      window_list_push(&backend->configure, e->as.configure_notify.window);
+      break;
     case ZDWM_EFFECT_CHANGE_BORDER_COLOR: {
       xcb_change_window_attributes_value_list_t value = {
         .border_pixel = e->as.change_border_color.color->argb
@@ -640,6 +647,46 @@ static void backend_merge_effects(
   }
 }
 
+static void batch_send_configure_notify(
+  xcb_connection_t *conn,
+  xcb_window_t *windows,
+  size_t count
+) {
+  if (count == 0) return;
+
+  auto cookie_list = p_new(xcb_get_geometry_cookie_t, count);
+
+  for (size_t i = 0; i < count; ++i) {
+    auto window = windows[i];
+    cookie_list[i] = xcb_get_geometry(conn, window);
+  }
+
+  uint32_t event_mask = XCB_EVENT_MASK_STRUCTURE_NOTIFY;
+  for (size_t i = 0; i < count; ++i) {
+    auto window = windows[i];
+    auto cookie = cookie_list[i];
+    auto reply = xcb_get_geometry_reply(conn, cookie, nullptr);
+    if (!reply) continue;
+
+    xcb_configure_notify_event_t ev = {
+      .response_type = XCB_CONFIGURE_NOTIFY,
+      .event = window,
+      .window = window,
+      .above_sibling = XCB_WINDOW_NONE,
+      .x = reply->x,
+      .y = reply->y,
+      .width = reply->width,
+      .height = reply->height,
+      .border_width = reply->border_width,
+      .override_redirect = false,
+    };
+    xcb_send_event(conn, false, window, event_mask, (char *)&ev);
+    p_delete(&reply);
+  }
+
+  p_delete(&cookie_list);
+}
+
 static void backend_batch_apply_effects(backend_t *backend) {
   xcb_connection_t *conn = backend->conn;
   if (backend->unmap.count) {
@@ -669,6 +716,12 @@ static void backend_batch_apply_effects(backend_t *backend) {
 
   backend_apply_window_configure_list(backend);
 
+  {
+    auto windows = backend->configure.windows;
+    auto count = backend->configure.count;
+    batch_send_configure_notify(conn, windows, count);
+  }
+
   if (backend->update_focus) {
     backend_focus_window(backend, backend->focus_window);
   }
@@ -684,6 +737,7 @@ bool backend_apply_effect(
   window_list_reset(&backend->unmap);
   window_list_reset(&backend->map);
   window_list_reset(&backend->kill);
+  window_list_reset(&backend->configure);
 
   backend_merge_effects(backend, effects, effect_count);
   backend_batch_apply_effects(backend);
@@ -774,7 +828,8 @@ void backend_scan_result_destroy(backend_scan_result_t *result) {
 backend_bar_window_t backend_create_bar_window(
   backend_t *backend,
   rect_t geometry,
-  uint32_t bg_pixel
+  uint32_t bg_pixel,
+  bool enable_tray
 ) {
   auto conn = backend->conn;
   auto root = backend->screen->root;
@@ -844,7 +899,24 @@ backend_bar_window_t backend_create_bar_window(
     fatal("cannot create cairo context: %s", cairo_status_to_string(statue));
   }
 
-  return (backend_bar_window_t){.window_id = window_id, .cr = cr};
+  if (enable_tray) {
+    tray_host_window_t host_window = {
+      .window = window_id,
+      .width = width,
+      .height = height,
+      .bg_pixel = bg_pixel,
+    };
+    tray_init(backend, host_window);
+  }
+
+  return (backend_bar_window_t){
+    .window_id = window_id,
+    .cr = cr,
+    .tray = {
+      .api = tray_api,
+      .handle = backend,
+    },
+  };
 }
 
 void backend_flush(backend_t *backend) { xcb_flush(backend->conn); }

src/backend/x11/event.c

@@ -10,6 +10,7 @@
 #include <xcb/xproto.h>
 
 #include "backend/x11/common.h"
+#include "backend/x11/tray.h"
 #include "backend/x11/window.h"
 #include "base/memory.h"
 #include "interface/backend.h"
@@ -189,6 +190,8 @@ static bool handle_map_request(
   event_t *event,
   const xcb_map_request_event_t *xcb_event
 ) {
+  if (tray_handle_map_request(backend, xcb_event)) return false;
+
   event->type = ZDWM_EVENT_WINDOW_MAP_REQUEST;
   return populate_window_event(
     backend,
@@ -202,6 +205,8 @@ static bool handle_unmap_notify(
   event_t *event,
   const xcb_unmap_notify_event_t *xcb_event
 ) {
+  if (tray_handle_unmap_notify(backend, xcb_event)) return false;
+
   event->type = ZDWM_EVENT_WINDOW_REMOVE;
   event->as.window_remove.window = xcb_event->window;
   if (XCB_EVENT_SENT(xcb_event)) {
@@ -218,6 +223,8 @@ static bool handle_destroy_notify(
   event_t *event,
   const xcb_destroy_notify_event_t *xcb_event
 ) {
+  if (tray_handle_destroy_notify(backend, xcb_event)) return false;
+
   event->type = ZDWM_EVENT_WINDOW_REMOVE;
   event->as.window_remove.window = xcb_event->window;
   event->as.window_remove.reason = ZDWM_WINDOW_REMOVE_DESTROY;
@@ -230,6 +237,8 @@ static bool handle_configure_request(
   event_t *event,
   const xcb_configure_request_event_t *xcb_event
 ) {
+  if (tray_handle_configure_request(backend, xcb_event)) return false;
+
   event->type = ZDWM_EVENT_CONFIGURE_REQUEST;
   auto data = &event->as.configure_request;
   data->window = xcb_event->window;
@@ -341,6 +350,8 @@ static bool handle_property_notify(
   event_t *event,
   const xcb_property_notify_event_t *xcb_event
 ) {
+  if (tray_handle_property_notify(backend, xcb_event)) return false;
+
   auto window_id = xcb_event->window;
   if (
     xcb_event->atom == backend->atoms.WM_NAME ||
@@ -419,6 +430,8 @@ static bool handle_client_message(
   event_t *event,
   const xcb_client_message_event_t *xcb_event
 ) {
+  if (tray_handle_client_message(backend, xcb_event)) return false;
+
   auto atoms = &backend->atoms;
 
   if (xcb_event->type == atoms->_NET_ACTIVE_WINDOW) {

src/backend/x11/internal.h

@@ -46,6 +46,10 @@
   X(_NET_WM_WINDOW_TYPE_NOTIFICATION)
 
 #define ATOM_LIST(X)          \
+  X(MANAGER)                  \
+  X(_NET_SYSTEM_TRAY_OPCODE)  \
+  X(_XEMBED)                  \
+                              \
   X(COMPOUND_TEXT)            \
   X(UTF8_STRING)              \
                               \
@@ -86,6 +90,8 @@ typedef enum cursor_t {
   ZDWM_CURSOR_COUNT,
 } cursor_t;
 
+typedef struct tray_host_t tray_host_t;
+
 typedef struct backend_t {
   xcb_key_symbols_t *key_symbols;
   xcb_connection_t *conn;
@@ -109,6 +115,9 @@ typedef struct backend_t {
   window_list_t unmap;
   window_list_t map;
   window_list_t kill;
+  window_list_t configure;
+
+  tray_host_t *tray;
 } backend_t;
 
 bool populate_window_event(

src/backend/x11/tray.c

@@ -0,0 +1,606 @@
+#include "backend/x11/tray.h"
+
+#include <assert.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <xcb/xcb.h>
+#include <xcb/xcb_aux.h>
+#include <xcb/xproto.h>
+#include <zdwm/types.h>
+
+#include "backend/x11/window.h"
+#include "base/array.h"
+#include "base/log.h"
+#include "base/macros.h"
+#include "base/memory.h"
+#include "interface/tray.h"
+#include "interface/types.h"
+#include "internal.h"
+
+typedef enum tray_opcode_t {
+  SYSTEM_TRAY_REQUEST_DOCK = 0,
+  SYSTEM_TRAY_BEGIN_MESSAGE = 1,
+  SYSTEM_TRAY_CANCEL_MESSAGE = 2,
+} tray_opcode_t;
+
+typedef enum xembed_message_t {
+  XEMBED_EMBEDDED_NOTIFY = 0,
+} xembed_message_t;
+
+static constexpr auto XEMBED_VERSION = 0;
+
+typedef struct tray_icon_t {
+  xcb_window_t window;
+  int32_t natural_width;
+  int32_t natural_height;
+} tray_icon_t;
+
+typedef struct tray_host_t {
+  bool enabled;
+  bool initialized;
+  xcb_atom_t selection_atom;
+  xcb_window_t host_window;
+  xcb_window_t container;
+  int32_t icon_size;
+
+  tray_icon_t *icons;
+  size_t icon_count;
+  size_t icon_capacity;
+
+  tray_icons_change_cb_t icon_change_cb;
+  void *cb_user_data;
+} tray_host_t;
+
+static tray_host_t *get_tray_host(void *handle) {
+  backend_t *backend = handle;
+  if (!backend) return nullptr;
+
+  auto tray = backend->tray;
+  if (!tray || !tray->enabled) return nullptr;
+
+  return tray;
+}
+
+static size_t tray_find_icon(tray_host_t *tray, xcb_window_t window) {
+  for (size_t i = 0; i < tray->icon_count; ++i) {
+    if (tray->icons[i].window == window) return i;
+  }
+
+  return SIZE_MAX;
+}
+
+static tray_icon_t *tray_get_icon(tray_host_t *tray, xcb_window_t window) {
+  for (size_t i = 0; i < tray->icon_count; ++i) {
+    auto icon = &tray->icons[i];
+    if (icon->window == window) return icon;
+  }
+
+  return nullptr;
+}
+
+static inline void tray_dispatch_callback(tray_host_t *tray) {
+  assert(tray);
+  if (tray->icon_change_cb) tray->icon_change_cb(tray->cb_user_data);
+}
+
+static void tray_release_icon_window(backend_t *backend, tray_icon_t *icon) {
+  if (!icon || icon->window == XCB_WINDOW_NONE) return;
+
+  auto tray = get_tray_host(backend);
+  if (!tray || !tray->initialized) return;
+
+  auto conn = backend->conn;
+  auto root = backend->screen->root;
+  auto window = icon->window;
+  auto mask = XCB_CW_EVENT_MASK;
+  xcb_params_cw_t params = {.event_mask = XCB_EVENT_MASK_NO_EVENT};
+  xcb_change_save_set(conn, XCB_SET_MODE_DELETE, window);
+  xcb_aux_change_window_attributes(conn, window, mask, &params);
+  xcb_reparent_window(conn, window, root, 0, 0);
+}
+
+static void tray_remove_icon_by_index(
+  backend_t *backend,
+  size_t index,
+  bool release_window
+) {
+  auto tray = backend->tray;
+  if (index >= tray->icon_count) return;
+
+  auto icon = &tray->icons[index];
+  if (release_window) tray_release_icon_window(backend, icon);
+
+  array_erase(tray->icons, tray->icon_count, index);
+  tray_dispatch_callback(tray);
+}
+
+static zdwm_size_t tray_get_icon_size(tray_host_t *tray, size_t index) {
+  auto target_size = MAX(tray->icon_size, (int32_t)1);
+  auto natural_width = tray->icons[index].natural_width;
+  auto natural_height = tray->icons[index].natural_height;
+
+  if (natural_width == 0) natural_width = target_size;
+  if (natural_height == 0) natural_height = target_size;
+
+  double width_scale = (double)target_size / (double)natural_width;
+  double height_scale = (double)target_size / (double)natural_height;
+  auto scale = MIN(width_scale, height_scale);
+  zdwm_size_t size = {
+    .width = (int32_t)(natural_width * scale),
+    .height = (int32_t)(natural_height * scale),
+  };
+  return size;
+}
+
+static void tray_layout_icons(backend_t *backend, int32_t start_x) {
+  auto tray = get_tray_host(backend);
+  if (!tray || !tray->initialized) return;
+  if (tray->container == XCB_WINDOW_NONE) return;
+
+  auto conn = backend->conn;
+  if (tray->icon_count == 0) {
+    xcb_unmap_window(conn, tray->container);
+    return;
+  }
+
+  auto height = tray->icon_size;
+  auto width = height * (int32_t)tray->icon_count;
+  xcb_configure_window_value_list_t value_list = {
+    .x = start_x,
+    .y = 0,
+    .width = (uint32_t)width,
+    .height = (uint32_t)height,
+  };
+  uint16_t value_mask = XCB_CONFIG_WINDOW_X | XCB_CONFIG_WINDOW_Y |
+                        XCB_CONFIG_WINDOW_WIDTH | XCB_CONFIG_WINDOW_HEIGHT;
+  xcb_configure_window_aux(conn, tray->container, value_mask, &value_list);
+  xcb_map_window(conn, tray->container);
+
+  for (size_t i = 0; i < tray->icon_count; ++i) {
+    auto window = tray->icons[i].window;
+    auto icon_size = tray_get_icon_size(tray, i);
+    value_mask |= XCB_CONFIG_WINDOW_BORDER_WIDTH;
+    auto offset_x = height * (int32_t)i;
+    value_list = (xcb_configure_window_value_list_t){
+      .x = offset_x + (icon_size.width - height) / 2,
+      .y = (icon_size.height - height) / 2,
+      .width = icon_size.width,
+      .height = icon_size.height,
+      .border_width = 0,
+    };
+    xcb_configure_window_aux(conn, window, value_mask, &value_list);
+    xcb_map_window(conn, window);
+  }
+}
+
+static window_id_t tray_host_window(void *handle) {
+  auto tray = get_tray_host(handle);
+  if (!tray) return ZDWM_WINDOW_ID_INVALID;
+
+  return tray->host_window;
+}
+
+static size_t tray_icon_count(void *handle) {
+  auto tray = get_tray_host(handle);
+
+  return tray ? tray->icon_count : 0;
+}
+
+static int32_t tray_icon_size(void *handle) {
+  auto tray = get_tray_host(handle);
+
+  return tray ? tray->icon_size : 0;
+}
+
+static void tray_place(void *handle, int32_t x) {
+  auto tray = get_tray_host(handle);
+  if (!tray) return;
+
+  tray_layout_icons((backend_t *)handle, x);
+}
+
+static void
+tray_set_listeners(void *handle, tray_icons_change_cb_t cb, void *user_data) {
+  auto tray = get_tray_host(handle);
+  if (!tray) return;
+
+  tray->icon_change_cb = cb;
+  tray->cb_user_data = user_data;
+}
+
+const tray_api_t tray_api = {
+  .host_window = tray_host_window,
+  .icon_count = tray_icon_count,
+  .icon_size = tray_icon_size,
+  .place = tray_place,
+  .set_listener = tray_set_listeners,
+};
+
+static bool tray_intern_selection_atom(tray_host_t *tray, backend_t *backend) {
+  auto conn = backend->conn;
+  auto screenp = backend->screenp;
+
+  char selection_name[64] = {0};
+  auto atom_name_format = "_NET_SYSTEM_TRAY_S%d";
+  snprintf(selection_name, sizeof(selection_name), atom_name_format, screenp);
+
+  uint16_t name_length = strlen(selection_name);
+  auto cookie = xcb_intern_atom(conn, false, name_length, selection_name);
+  auto reply = xcb_intern_atom_reply(conn, cookie, nullptr);
+  if (!reply) {
+    warn("cannot intern tray selection atom: %s", selection_name);
+    return false;
+  }
+
+  tray->selection_atom = reply->atom;
+  p_delete(&reply);
+  return true;
+}
+
+static bool tray_create_container_window(
+  tray_host_t *tray,
+  backend_t *backend,
+  tray_host_window_t host_window
+) {
+  auto conn = backend->conn;
+  auto window_id = xcb_generate_id(conn);
+  auto depth = backend->screen->root_depth;
+  auto visual_id = backend->screen->root_visual;
+
+  static xcb_colormap_t colormap = XCB_NONE;
+  if (colormap == XCB_NONE) {
+    colormap = xcb_generate_id(conn);
+    auto root = backend->screen->root;
+    uint8_t alloc = XCB_COLORMAP_ALLOC_NONE;
+    xcb_create_colormap(conn, alloc, colormap, root, visual_id);
+  }
+
+  uint32_t value_mask = XCB_CW_BACK_PIXEL | XCB_CW_BORDER_PIXEL |
+                        XCB_CW_OVERRIDE_REDIRECT | XCB_CW_EVENT_MASK |
+                        XCB_CW_COLORMAP;
+  xcb_create_window_value_list_t value_list = {
+    .background_pixel = host_window.bg_pixel,
+    .border_pixel = 0,
+    .override_redirect = true,
+    .event_mask =
+      XCB_EVENT_MASK_SUBSTRUCTURE_NOTIFY | XCB_EVENT_MASK_STRUCTURE_NOTIFY,
+    .colormap = colormap,
+  };
+  auto cookie = xcb_create_window_aux_checked(
+    conn,
+    depth,
+    window_id,
+    host_window.window,
+    (int16_t)host_window.width,
+    0,
+    1,
+    (uint16_t)MAX(1, host_window.height),
+    0,
+    XCB_WINDOW_CLASS_INPUT_OUTPUT,
+    visual_id,
+    value_mask,
+    &value_list
+  );
+
+  if (xcb_request_check(conn, cookie)) {
+    warn("cannot create system tray container window: 0x%x", window_id);
+    return false;
+  }
+
+  tray->container = window_id;
+
+  window_set_class_instance(conn, window_id);
+
+#define TRAY_CONTAINER_WINDOW_NAME APP_NAME "_tray"
+  window_set_name_static(conn, window_id, TRAY_CONTAINER_WINDOW_NAME);
+  auto name = TRAY_CONTAINER_WINDOW_NAME;
+  auto name_len = sizeof(TRAY_CONTAINER_WINDOW_NAME) - 1;
+#undef TRAY_CONTAINER_WINDOW_NAME
+
+  uint8_t mode = XCB_PROP_MODE_REPLACE;
+  auto atoms = &backend->atoms;
+  auto prop = atoms->_NET_WM_NAME;
+  auto type = atoms->UTF8_STRING;
+  xcb_change_property(conn, mode, window_id, prop, type, 8, name_len, name);
+
+  return true;
+}
+
+static bool tray_take_selection_owner(tray_host_t *tray, backend_t *backend) {
+  auto conn = backend->conn;
+  auto atom = tray->selection_atom;
+  auto cookie = xcb_get_selection_owner(conn, atom);
+  auto reply = xcb_get_selection_owner_reply(conn, cookie, nullptr);
+  if (reply && reply->owner != XCB_WINDOW_NONE) {
+    warn(
+      "system tray selection is already owned by window: 0x%x",
+      reply->owner
+    );
+    p_delete(&reply);
+    return false;
+  }
+
+  p_delete(&reply);
+
+  auto owner = tray->container;
+  xcb_set_selection_owner(conn, owner, atom, XCB_CURRENT_TIME);
+
+  cookie = xcb_get_selection_owner(conn, atom);
+  reply = xcb_get_selection_owner_reply(conn, cookie, nullptr);
+  bool success = reply && reply->owner == owner;
+  p_delete(&reply);
+
+  if (!success) warn("cannot acquire system tray selection");
+  return success;
+}
+
+static void tray_broadcast_manager(tray_host_t *tray, backend_t *backend) {
+  auto conn = backend->conn;
+  auto root = backend->screen->root;
+
+  xcb_client_message_event_t event = {
+    .response_type = XCB_CLIENT_MESSAGE,
+    .window = root,
+    .format = 32,
+    .type = backend->atoms.MANAGER,
+    .data.data32 = {
+      [0] = XCB_CURRENT_TIME,
+      [1] = tray->selection_atom,
+      [2] = tray->container,
+    },
+  };
+  uint32_t event_mask = XCB_EVENT_MASK_STRUCTURE_NOTIFY;
+  xcb_send_event(conn, false, root, event_mask, (char *)&event);
+}
+
+void tray_init(backend_t *backend, tray_host_window_t host_window) {
+  auto tray = get_tray_host(backend);
+  if (!tray) {
+    tray = p_new(tray_host_t, 1);
+    backend->tray = tray;
+  }
+
+  if (tray->initialized) return;
+
+  if (!tray_intern_selection_atom(tray, backend)) return;
+
+  if (!tray_create_container_window(tray, backend, host_window)) return;
+  if (!tray_take_selection_owner(tray, backend)) {
+    tray_cleanup(backend);
+    return;
+  }
+
+  tray->enabled = true;
+  tray->initialized = true;
+  tray->host_window = host_window.window;
+  tray->icon_size = host_window.height;
+
+  tray_broadcast_manager(tray, backend);
+  tray_layout_icons(backend, host_window.width);
+  xcb_flush(backend->conn);
+}
+
+void tray_cleanup(backend_t *backend) {
+  auto tray = backend->tray;
+  if (!tray) return;
+
+  for (size_t i = 0; i < tray->icon_count; ++i) {
+    tray_release_icon_window(backend, &tray->icons[i]);
+  }
+  p_delete(&tray->icons);
+  tray->icon_count = 0;
+  tray->icon_capacity = 0;
+
+  auto conn = backend->conn;
+
+  auto atom = tray->selection_atom;
+  if (atom != XCB_ATOM_NONE) {
+    xcb_set_selection_owner(conn, XCB_WINDOW_NONE, atom, XCB_CURRENT_TIME);
+  }
+
+  if (tray->container != XCB_WINDOW_NONE) {
+    xcb_destroy_window(conn, tray->container);
+  }
+
+  p_clear(backend->tray, 1);
+  p_delete(&backend->tray);
+}
+
+static void
+tray_select_icon_events(xcb_connection_t *conn, xcb_window_t window) {
+  xcb_params_cw_t params = {
+    .event_mask =
+      XCB_EVENT_MASK_STRUCTURE_NOTIFY | XCB_EVENT_MASK_PROPERTY_CHANGE,
+  };
+  uint32_t mask = XCB_CW_EVENT_MASK;
+  xcb_aux_change_window_attributes(conn, window, mask, &params);
+  xcb_clear_area(conn, false, window, 0, 0, 0, 0);
+}
+
+/* reference:
+ * https://specifications.freedesktop.org/xembed/latest-single/#id-1.7.4 */
+typedef struct xembed_message_data_t {
+  uint32_t message; /* message opcode */
+  uint32_t detail;  /* message detail */
+  uint32_t data1;   /* message data 1 */
+  uint32_t data2;   /* message data 2 */
+} xembed_message_data_t;
+
+static void tray_send_xembed_message(
+  backend_t *backend,
+  xcb_window_t window,
+  xembed_message_data_t message
+) {
+  auto conn = backend->conn;
+  auto message_type = backend->atoms._XEMBED;
+
+  xcb_client_message_event_t event = {
+    .response_type = XCB_CLIENT_MESSAGE,
+    .format = 32,
+    .window = window,
+    .type = message_type,
+    .data.data32 = {
+      [0] = XCB_CURRENT_TIME,
+      [1] = message.message,
+      [2] = message.detail,
+      [3] = message.data1,
+      [4] = message.data2,
+    },
+  };
+  uint32_t event_mask = XCB_EVENT_MASK_NO_EVENT;
+  xcb_send_event(conn, false, window, event_mask, (char *)&event);
+}
+
+static void tray_add_icon(backend_t *backend, xcb_window_t window) {
+  if (window == XCB_WINDOW_NONE) return;
+
+  auto tray = get_tray_host(backend);
+  if (!tray || !tray->initialized || tray_get_icon(tray, window)) return;
+
+  rect_t geometry = {0};
+  if (!window_get_geometry(backend, window, &geometry)) return;
+
+  auto icon = array_push(tray->icons, tray->icon_count, tray->icon_capacity);
+  *icon = (tray_icon_t){
+    .window = window,
+    .natural_width = geometry.width,
+    .natural_height = geometry.height,
+  };
+
+  auto conn = backend->conn;
+  auto container = tray->container;
+  xembed_message_data_t message = {
+    .message = XEMBED_EMBEDDED_NOTIFY,
+    .detail = 0,
+    .data1 = container,
+    .data2 = XEMBED_VERSION,
+  };
+  xcb_change_save_set(conn, XCB_SET_MODE_INSERT, window);
+  xcb_reparent_window(conn, window, tray->container, 0, 0);
+  tray_select_icon_events(conn, window);
+  tray_send_xembed_message(backend, window, message);
+  xcb_map_window(conn, window);
+  tray_dispatch_callback(tray);
+}
+
+bool tray_handle_client_message(
+  backend_t *backend,
+  const xcb_client_message_event_t *ev
+) {
+  auto tray = get_tray_host(backend);
+  if (!tray || !tray->enabled || !tray->initialized) return false;
+  if (ev->window != tray->container && ev->window != backend->screen->root) {
+    return false;
+  }
+
+  auto opcode = ev->data.data32[1];
+  switch (opcode) {
+  case SYSTEM_TRAY_REQUEST_DOCK:
+    auto window = ev->data.data32[2];
+    tray_add_icon(backend, window);
+    break;
+  case SYSTEM_TRAY_BEGIN_MESSAGE:
+  case SYSTEM_TRAY_CANCEL_MESSAGE:
+  default:
+    break;
+  }
+
+  xcb_flush(backend->conn);
+
+  return true;
+}
+
+bool tray_handle_configure_request(
+  backend_t *backend,
+  const xcb_configure_request_event_t *ev
+) {
+  auto tray = get_tray_host(backend);
+  if (!tray || !tray->initialized) return false;
+
+  if (ev->window == tray->container) {
+    tray_dispatch_callback(tray);
+    return true;
+  }
+
+  auto icon = tray_get_icon(tray, ev->window);
+  if (!icon) return false;
+
+  if ((ev->value_mask & XCB_CONFIG_WINDOW_WIDTH) && ev->width > 0) {
+    icon->natural_width = (int32_t)ev->width;
+  }
+  if ((ev->value_mask & XCB_CONFIG_WINDOW_HEIGHT) && ev->height > 0) {
+    icon->natural_height = (int32_t)ev->height;
+  }
+
+  tray_dispatch_callback(tray);
+  return true;
+}
+
+bool tray_handle_map_request(
+  backend_t *backend,
+  const xcb_map_request_event_t *ev
+) {
+  auto tray = get_tray_host(backend);
+  if (!tray || !tray->initialized) return false;
+
+  auto conn = backend->conn;
+  if (ev->window == tray->container) {
+    tray_dispatch_callback(tray);
+    return true;
+  }
+
+  auto icon = tray_get_icon(tray, ev->window);
+  if (!icon && ev->parent != tray->container) return false;
+
+  xcb_map_window(conn, ev->window);
+  xcb_flush(conn);
+
+  tray_dispatch_callback(tray);
+  return true;
+}
+
+bool tray_handle_property_notify(
+  backend_t *backend,
+  const xcb_property_notify_event_t *ev
+) {
+  auto tray = get_tray_host(backend);
+  if (!tray || !tray->initialized) return false;
+
+  if (ev->window == XCB_WINDOW_NONE) return false;
+  if (ev->window == tray->container) return true;
+  return tray_get_icon(tray, ev->window) != nullptr;
+}
+
+bool tray_handle_unmap_notify(
+  backend_t *backend,
+  const xcb_unmap_notify_event_t *ev
+) {
+  auto tray = get_tray_host(backend);
+  if (!tray || !tray->initialized) return false;
+
+  auto index = tray_find_icon(tray, ev->window);
+  if (index == SIZE_MAX) return ev->window == tray->container;
+
+  tray_remove_icon_by_index(backend, index, true);
+  return true;
+}
+
+bool tray_handle_destroy_notify(
+  backend_t *backend,
+  const xcb_destroy_notify_event_t *ev
+) {
+  auto tray = get_tray_host(backend);
+  if (!tray || !tray->initialized) return false;
+
+  if (ev->window == tray->container) {
+    tray_cleanup(backend);
+    return true;
+  }
+
+  auto index = tray_find_icon(tray, ev->window);
+  if (index == SIZE_MAX) return false;
+
+  tray_remove_icon_by_index(backend, index, false);
+  return true;
+}

src/backend/x11/tray.h

@@ -0,0 +1,45 @@
+#pragma once
+
+#include <stdint.h>
+#include <xcb/xproto.h>
+
+#include "interface/tray.h"
+
+extern const tray_api_t tray_api;
+
+typedef struct backend_t backend_t;
+
+typedef struct tray_host_window_t {
+  xcb_window_t window;
+  int32_t width;
+  int32_t height;
+  uint32_t bg_pixel;
+} tray_host_window_t;
+
+void tray_init(backend_t *backend, tray_host_window_t host_window);
+void tray_cleanup(backend_t *backend);
+
+bool tray_handle_client_message(
+  backend_t *backend,
+  const xcb_client_message_event_t *ev
+);
+bool tray_handle_configure_request(
+  backend_t *backend,
+  const xcb_configure_request_event_t *ev
+);
+bool tray_handle_map_request(
+  backend_t *backend,
+  const xcb_map_request_event_t *ev
+);
+bool tray_handle_property_notify(
+  backend_t *backend,
+  const xcb_property_notify_event_t *ev
+);
+bool tray_handle_unmap_notify(
+  backend_t *backend,
+  const xcb_unmap_notify_event_t *ev
+);
+bool tray_handle_destroy_notify(
+  backend_t *backend,
+  const xcb_destroy_notify_event_t *ev
+);

src/bar/bar.c

@@ -12,6 +12,7 @@
 #include "bar/binding.h"
 #include "bar/cell.h"
 #include "bar/text.h"
+#include "bar/tray.h"
 #include "bar/types.h"
 #include "bar/windows.h"
 #include "bar/workspaces.h"
@@ -130,9 +131,14 @@ static void bar_output_add_windows(
   bar_windows_add_listeners(listeners, item->state);
 }
 
+static inline void bar_output_add_tray(bar_output_t *bar_output, tray_t *tray) {
+  bar_add_item(bar_output->output_id, &bar_output->right, bar_tray, tray);
+}
+
 void bar_init(bar_t *bar, listeners_t *listeners) {
   auto c = &bar->config;
   bar->ctx = text_context_create(c->font_family, c->font_size, c->dpi);
+  auto tray = &bar->tray;
 
   for (size_t i = 0; i < bar->count; ++i) {
     auto bar_output = &bar->bars[i];
@@ -141,6 +147,10 @@ void bar_init(bar_t *bar, listeners_t *listeners) {
     bar_output_add_workspace(bar_output, &bar->config, listeners);
     bar_output_add_binding(bar_output, &bar->config, listeners);
     bar_output_add_windows(bar_output, &bar->config, listeners);
+
+    if (tray->api.host_window(tray->handle) == bar_output->window_id) {
+      bar_output_add_tray(bar_output, &bar->tray);
+    }
   }
 
   bar->timerfd = time_create_monotonic_timerfd_by_fps(bar->config.fps);
@@ -212,14 +222,16 @@ static void bar_output_layout(bar_output_t *bar_output, text_context_t *ctx) {
     item->region.start = start;
     for (size_t j = 0; j < item->count; ++j) {
       auto cell = &item->cells[j];
+      auto fixed_width = cell->fixed_width;
 
-      int32_t width = 0;
-      text_context_get_text_size(ctx, cell->text, &width, nullptr);
-
-      bar_x_region_t region = {
-        .start = start,
-        .end = start + width + item->cell_padding * 2,
-      };
+      bar_x_region_t region = {.start = start, .end = start};
+      if (fixed_width == 0) {
+        int32_t width = 0;
+        text_context_get_text_size(ctx, cell->text, &width, nullptr);
+        region.end += width + 2 * item->cell_padding;
+      } else if (fixed_width > 0) {
+        region.end += fixed_width;
+      }
       bar_cell_set_region(item, j, region);
 
       start = region.end;
@@ -240,14 +252,16 @@ static void bar_output_layout(bar_output_t *bar_output, text_context_t *ctx) {
     for (size_t j = item->count; j > 0; --j) {
       auto cell_index = j - 1;
       auto cell = &item->cells[cell_index];
+      auto fixed_width = cell->fixed_width;
 
-      int32_t width = 0;
-      text_context_get_text_size(ctx, cell->text, &width, nullptr);
-
-      bar_x_region_t region = {
-        .start = end - width - item->cell_padding * 2,
-        .end = end,
-      };
+      bar_x_region_t region = {.start = end, .end = end};
+      if (fixed_width == 0) {
+        int32_t width = 0;
+        text_context_get_text_size(ctx, cell->text, &width, nullptr);
+        region.start -= width + item->cell_padding * 2;
+      } else if (fixed_width > 0) {
+        region.start -= fixed_width;
+      }
       bar_cell_set_region(item, cell_index, region);
 
       end = region.start;
@@ -263,12 +277,30 @@ static void bar_output_layout(bar_output_t *bar_output, text_context_t *ctx) {
   if (center->count == 0) return;
   center->region = (bar_x_region_t){.start = start, .end = end};
 
-  auto width = (end - start) / (int32_t)center->count;
+  auto center_width = end - start;
+  auto center_count = center->count;
   for (size_t i = 0; i < center->count; ++i) {
-    bar_x_region_t region = {
-      .start = start,
-      .end = start + width + center->cell_padding * 2,
-    };
+    auto cell = &center->cells[i];
+    auto fixed_width = cell->fixed_width;
+    if (fixed_width > 0) {
+      center_width -= fixed_width;
+    } else if (fixed_width < 0) {
+      /* 隐藏的 cell 不占任何空间，平分宽度时不参与 */
+      --center_count;
+    }
+  }
+
+  auto width = center_width / (int32_t)center_count;
+  for (size_t i = 0; i < center->count; ++i) {
+    auto cell = &center->cells[i];
+    auto fixed_width = cell->fixed_width;
+
+    bar_x_region_t region = {.start = start, .end = start};
+    if (fixed_width == 0) {
+      region.end += width + center->cell_padding * 2;
+    } else if (fixed_width > 0) {
+      region.end += fixed_width;
+    }
     start = region.end;
     bar_cell_set_region(center, i, region);
   }
@@ -386,6 +418,42 @@ bar_output_draw(bar_output_t *bar_output, text_context_t *ctx, color_t *bg) {
   bar_item_draw(cr, &bar_output->center, ctx, bar_output->height);
 }
 
+static inline void bar_item_run_hook(
+  zdwm_bar_item_t *item,
+  void (*hook)(const zdwm_bar_item_hook_params_t *params)
+) {
+  if (!hook) return;
+
+  zdwm_bar_item_hook_params_t params = {
+    .item = item,
+    .cell_api = &bar_cell_api,
+    .region = item->region,
+    .state = item->state
+  };
+  hook(&params);
+}
+
+static void visitor_after_layout(zdwm_bar_item_t *item) {
+  bar_item_run_hook(item, item->api.after_layout);
+}
+
+static void visitor_after_draw(zdwm_bar_item_t *item) {
+  bar_item_run_hook(item, item->api.after_draw);
+}
+
+typedef void (*bar_item_visitor_t)(zdwm_bar_item_t *item);
+
+static void
+bar_output_foreach_item(bar_output_t *bar_output, bar_item_visitor_t visit) {
+  for (size_t i = 0; i < bar_output->left.count; ++i) {
+    visit(&bar_output->left.items[i]);
+  }
+  visit(&bar_output->center);
+  for (size_t i = 0; i < bar_output->right.count; ++i) {
+    visit(&bar_output->right.items[i]);
+  }
+}
+
 bool bar_draw(bar_t *bar) {
   auto ctx = bar->ctx;
 
@@ -396,7 +464,9 @@ bool bar_draw(bar_t *bar) {
     if (!bar_output_is_dirty(bar_output)) continue;
 
     bar_output_layout(bar_output, ctx);
+    bar_output_foreach_item(bar_output, visitor_after_layout);
     bar_output_draw(bar_output, ctx, &bar->palette.bg);
+    bar_output_foreach_item(bar_output, visitor_after_draw);
     changed = true;
   }
 

src/bar/bar.h

@@ -11,6 +11,7 @@
 #include "bar/types.h"
 #include "base/color.h"
 #include "common/listeners.h"
+#include "interface/tray.h"
 
 typedef struct bar_output_t {
   cairo_t *cr;
@@ -37,6 +38,7 @@ typedef struct bar_t {
   zdwm_bar_config_t config;
   bar_palette_t palette;
   text_context_t *ctx;
+  tray_t tray;
 } bar_t;
 
 void bar_init(bar_t *bar, listeners_t *listeners);

src/bar/cell.c

@@ -2,6 +2,7 @@
 
 #include <assert.h>
 #include <stddef.h>
+#include <stdint.h>
 #include <string.h>
 #include <strings.h>
 #include <zdwm/types.h>
@@ -119,15 +120,37 @@ bar_cell_set_indicator(zdwm_bar_item_t *item, size_t index, bool show) {
   item->dirty = true;
 }
 
+static void
+bar_cell_set_fixed_width(zdwm_bar_item_t *item, size_t index, int32_t width) {
+  if (index >= item->count) return;
+
+  auto cell = &item->cells[index];
+  if (cell->fixed_width == width) return;
+
+  cell->fixed_width = width;
+
+  cell->dirty = true;
+  item->dirty = true;
+}
+
+static bar_x_region_t bar_cell_get_region(zdwm_bar_item_t *item, size_t index) {
+  if (index >= item->count) return (bar_x_region_t){0};
+
+  auto cell = &item->cells[index];
+  return cell->region;
+}
+
 /* clang-format off */
-zdwm_bar_cell_api_t bar_cell_api = {
-  .get_cell_count     = bar_cell_get_count,
-  .set_cell_count     = bar_cell_set_count,
-  .cell_set_text      = bar_cell_set_text,
-  .cell_set_bg        = bar_cell_set_bg,
-  .cell_set_fg        = bar_cell_set_fg,
-  .cell_set_icon      = bar_cell_set_icon,
-  .cell_set_indicator = bar_cell_set_indicator,
+const zdwm_bar_cell_api_t bar_cell_api = {
+  .get_cell_count       = bar_cell_get_count,
+  .set_cell_count       = bar_cell_set_count,
+  .cell_set_text        = bar_cell_set_text,
+  .cell_set_bg          = bar_cell_set_bg,
+  .cell_set_fg          = bar_cell_set_fg,
+  .cell_set_icon        = bar_cell_set_icon,
+  .cell_set_indicator   = bar_cell_set_indicator,
+  .cell_set_fixed_width = bar_cell_set_fixed_width,
+  .cell_get_region      = bar_cell_get_region,
 };
 /* clang-format on */
 

src/bar/cell.h

@@ -12,4 +12,4 @@ void bar_cell_set_region(
   bar_x_region_t region
 );
 
-extern zdwm_bar_cell_api_t bar_cell_api;
+extern const zdwm_bar_cell_api_t bar_cell_api;

src/bar/tray.c

@@ -0,0 +1,78 @@
+#include "bar/tray.h"
+
+#include <assert.h>
+#include <stddef.h>
+#include <zdwm/bar.h>
+#include <zdwm/types.h>
+
+#include "base/memory.h"
+#include "interface/tray.h"
+
+typedef struct bar_tray_state_t {
+  tray_t tray;
+  bool dirty;
+} bar_tray_state_t;
+
+static void bar_tray_icons_changed(void *user_data) {
+  bar_tray_state_t *state = user_data;
+  state->dirty = true;
+}
+
+static void *bar_tray_create_state(zdwm_output_id_t output_id, void *config) {
+  tray_t *tray = config;
+  assert(tray != nullptr);
+
+  auto state = p_new(bar_tray_state_t, 1);
+  state->tray = *tray;
+  tray->api.set_listener(tray->handle, bar_tray_icons_changed, state);
+
+  return state;
+}
+
+static void bar_tray_update(
+  zdwm_bar_item_t *item,
+  const zdwm_bar_cell_api_t *cell_api,
+  void *state
+) {
+  bar_tray_state_t *data = state;
+  if (!data->dirty) return;
+
+  auto tray_handle = data->tray.handle;
+  auto tray_api = &data->tray.api;
+  auto icon_count = tray_api->icon_count(tray_handle);
+  auto cell_count = cell_api->get_cell_count(item);
+  if (cell_count == icon_count) {
+    data->dirty = false;
+    return;
+  }
+
+  cell_api->set_cell_count(item, icon_count);
+  auto cell_width = tray_api->icon_size(tray_handle);
+  for (size_t i = 0; i < icon_count; ++i) {
+    cell_api->cell_set_fixed_width(item, i, cell_width);
+  }
+
+  data->dirty = false;
+}
+
+static void bar_tray_after_layout(const zdwm_bar_item_hook_params_t *params) {
+  bar_tray_state_t *state = params->state;
+  auto tray_handle = state->tray.handle;
+  auto tray_api = &state->tray.api;
+  tray_api->place(tray_handle, params->region.start);
+}
+
+static void bar_tray_destroy_state(void *state) {
+  if (!state) return;
+
+  bar_tray_state_t *data = state;
+  p_delete(&data);
+}
+
+zdwm_bar_item_type_t bar_tray = {
+  .create_state = bar_tray_create_state,
+  .update = bar_tray_update,
+  .after_layout = bar_tray_after_layout,
+  .destroy_state = bar_tray_destroy_state,
+  .update_interval_ms = 0,
+};

src/bar/tray.h

@@ -0,0 +1,5 @@
+#pragma once
+
+#include <zdwm/bar.h>
+
+extern zdwm_bar_item_type_t bar_tray;

src/bar/types.h

@@ -7,10 +7,7 @@
 
 #include "base/color.h"
 
-typedef struct bar_x_region_t {
-  int32_t start;
-  int32_t end;
-} bar_x_region_t;
+typedef struct zdwm_bar_x_region_t bar_x_region_t;
 
 typedef struct bar_cell_t {
   zdwm_icon_t icon;
@@ -20,6 +17,7 @@ typedef struct bar_cell_t {
   color_t fg;
   color_t bg;
   bar_x_region_t region;
+  int32_t fixed_width;
   bool show_indicator;
   bool dirty;
 } bar_cell_t;

src/base/time.c

@@ -1,7 +1,5 @@
 #include "base/time.h"
 
-#include <bits/time.h>
-#include <bits/types/struct_itimerspec.h>
 #include <errno.h>
 #include <stdint.h>
 #include <string.h>

src/config/defaults.c

@@ -122,7 +122,7 @@ bool config_defaults_build(
   RAISE_OR_RUN(default_mode, Super("e"), editor);
   RAISE_OR_RUN(default_mode, Super("q"), browser);
   RAISE_OR_RUN(default_mode, Super("a"), chrome);
-  BIND_DEFAULT(Super("f"), {.type = ZDWM_ACTION_WINDOW_TOGGLE_FLOATING});
+  BIND_DEFAULT(Super("f"), {.type = ZDWM_ACTION_WINDOW_TOGGLE_FULLSCREEN});
   BIND_DEFAULT(Super("m"), {.type = ZDWM_ACTION_WINDOW_TOGGLE_MAXIMIZE});
   BIND_DEFAULT(
     Super("Control+space"),

src/core/command.h

@@ -11,6 +11,7 @@ typedef enum command_type_t {
   ZDWM_COMMAND_RAISE_WINDOW,
   ZDWM_COMMAND_WITHDRAW_WINDOW,
   ZDWM_COMMAND_CONFIGURE_WINDOW,
+  ZDWM_COMMAND_NOTIFY_CONFIGURE,
   ZDWM_COMMAND_CHANGE_WINDOW_STATE,
   ZDWM_COMMAND_START_MOVE_WINDOW,
   ZDWM_COMMAND_STOP_MOVE_WINDOW,
@@ -102,6 +103,7 @@ typedef struct command_t {
     only_window_data_t raise;
     only_window_data_t withdraw;
     configure_data_t configure;
+    only_window_data_t notify_configure;
     window_state_change_command_t state_change;
     start_interaction_command_t move;
     start_interaction_command_t resize;

src/core/listeners.c

@@ -5,6 +5,7 @@
 #include "core/binding.h"
 #include "core/layout.h"
 #include "core/state.h"
+#include "core/window.h"
 
 #define FOR_EACH_LISTENER(FIELD, BODY)         \
   do {                                         \
@@ -117,7 +118,7 @@ static bool listeners_window_snapshot(
   *out = (zdwm_window_t){
     .workspace = window->workspace_id,
     .id = window->id,
-    .title = window->title,
+    .title = window_get_showing_title(window),
     .focused = workspace->focused_window_id == window->id,
     .urgent = window->urgent,
     .skip_taskbar = window->skip_taskbar,

src/core/plan.c

@@ -121,6 +121,16 @@ void plan_push_resize_effect(plan_t *plan, window_id_t window_id) {
   plan_push_effect(plan, &effect);
 }
 
+void plan_push_configure_notify_effect(plan_t *plan, window_id_t window_id) {
+  if (window_id_invalid(window_id)) return;
+
+  effect_t effect = {
+    .type = ZDWM_EFFECT_CONFIGURE_NOTIFY,
+    .as.configure_notify.window = window_id,
+  };
+  plan_push_effect(plan, &effect);
+}
+
 void plan_push_fullscreen_effect(
   plan_t *plan,
   window_id_t window_id,

src/core/plan.h

@@ -26,6 +26,7 @@ void plan_push_kill_effect(plan_t *plan, window_id_t window_id);
 void plan_push_withdraw_effect(plan_t *plan, window_id_t window_id);
 void plan_push_move_effect(plan_t *plan, window_id_t window_id);
 void plan_push_resize_effect(plan_t *plan, window_id_t window_id);
+void plan_push_configure_notify_effect(plan_t *plan, window_id_t window_id);
 void plan_push_fullscreen_effect(
   plan_t *plan,
   window_id_t window_id,

src/core/policy.c

@@ -771,6 +771,15 @@ static void route_window_state_request(
   command_buffer_push(out, &change_window_state_cmd);
 }
 
+static void
+add_notify_configure_command(command_buffer_t *out, window_id_t window) {
+  command_t notify_cmd = {
+    .type = ZDWM_COMMAND_NOTIFY_CONFIGURE,
+    .as.notify_configure = {.window = window},
+  };
+  command_buffer_push(out, &notify_cmd);
+}
+
 static void route_configure_request(
   state_t *state,
   const configure_data_t *data,
@@ -788,6 +797,7 @@ static void route_configure_request(
   }
 
   if (!state_workspace_show(state, window->workspace_id)) return;
+  add_notify_configure_command(out, data->window);
   if (window_need_layout(window)) return;
   auto workspace = state_workspace_get(state, window->workspace_id);
   if (layout_get(layouts, workspace->layout_id)) return;
@@ -938,10 +948,13 @@ static void manage_window(
   auto window = state_window_add(state, &command->info);
   auto window_id = window->id;
   auto workspace_id = command->workspace;
+  auto workspace = state_workspace_get(state, workspace_id);
+  auto old_focused_window = workspace->focused_window_id;
   state_window_set_workspace(state, window_id, workspace_id);
   set_foucs_window(ctx, workspace_id, window_id, plan);
   plan_push_grab_button_effect(plan, window_id);
   push_window_list_effect(state, plan);
+  listeners_notify_window_updated(ctx->listeners, state, old_focused_window);
   listeners_notify_window_added(ctx->listeners, state, window_id);
 
   if (window_should_fix_size(window)) {
@@ -950,7 +963,6 @@ static void manage_window(
     state_window_set_floating(state, window_id, command->floating);
   }
 
-  auto workspace = state_workspace_get(state, workspace_id);
   auto need_layout = window_need_layout(window);
   auto layout_func = layout_get(ctx->layouts, workspace->layout_id);
 
@@ -1690,6 +1702,9 @@ void policy_apply_command(
     case ZDWM_COMMAND_CONFIGURE_WINDOW:
       configure_window(state, &cmd->as.configure, plan);
       break;
+    case ZDWM_COMMAND_NOTIFY_CONFIGURE:
+      plan_push_configure_notify_effect(plan, cmd->as.notify_configure.window);
+      break;
     case ZDWM_COMMAND_CHANGE_WINDOW_STATE:
       change_window_state(ctx, &cmd->as.state_change, plan);
       break;

src/core/window.c

@@ -145,3 +145,11 @@ bool window_can_resize(const window_t *window) {
 
   return true;
 }
+
+const char *window_get_showing_title(const window_t *window) {
+  if (window->title) return window->title;
+  if (window->instance_name) return window->instance_name;
+  if (window->class_name) return window->class_name;
+  if (window->app_id) return window->app_id;
+  return nullptr;
+}

src/core/window.h

@@ -67,3 +67,4 @@ bool window_need_resize(const window_t *window, int32_t width, int32_t height);
 bool window_should_has_border(const window_t *window);
 bool window_should_fix_size(const window_t *window);
 bool window_can_resize(const window_t *window);
+const char *window_get_showing_title(const window_t *window);

src/interface/backend.h

@@ -5,6 +5,7 @@
 
 #include "interface/effect.h"
 #include "interface/event.h"
+#include "interface/tray.h"
 #include "interface/types.h"
 
 typedef struct backend_t backend_t;
@@ -69,11 +70,13 @@ void backend_scan_result_destroy(backend_scan_result_t *result);
 typedef struct backend_bar_window_t {
   window_id_t window_id;
   cairo_t *cr;
+  tray_t tray;
 } backend_bar_window_t;
 
 backend_bar_window_t backend_create_bar_window(
   backend_t *backend,
   rect_t geometry,
-  uint32_t bg_pixel
+  uint32_t bg_pixel,
+  bool enable_tray
 );
 void backend_flush(backend_t *backend);

src/interface/effect.h

@@ -17,6 +17,7 @@ typedef enum effect_type_t {
   ZDWM_EFFECT_MAXIMIZE_WINDOW,
   ZDWM_EFFECT_FULLSCREEN_WINDOW,
   ZDWM_EFFECT_CONFIGURE_WINDOW,
+  ZDWM_EFFECT_CONFIGURE_NOTIFY,
   ZDWM_EFFECT_CHANGE_BORDER_COLOR,
   ZDWM_EFFECT_CHANGE_WINDOW_LIST,
   ZDWM_EFFECT_RESTACK_WINDOWS,
@@ -86,6 +87,7 @@ typedef struct effect_t {
     effect_bool_window_t maximize;
     effect_bool_window_t fullscreen;
     configure_data_t configure;
+    only_window_data_t configure_notify;
     effect_change_border_color_t change_border_color;
     effect_window_list_t change_window_list;
     effect_window_list_t restack_windows;

src/interface/tray.h

@@ -0,0 +1,35 @@
+#pragma once
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "interface/types.h"
+
+typedef void (*tray_icons_change_cb_t)(void *user_data);
+
+typedef struct tray_api_t {
+  /**
+   * @brief 获取 tray 当前挂载的 bar window id
+   *
+   * @detail    如果返回的 window_id 是 ZDWM_WINDOW_ID_INVALID 则表示 tray
+   *            功能未开启，无 tray 需要挂载
+   */
+  window_id_t (*host_window)(void *handle);
+  /* 获取当前 icon 数量 */
+  size_t (*icon_count)(void *handle);
+  /* 获取每个 icon 的边长， icon 长宽一样，都等于 bar_height */
+  int32_t (*icon_size)(void *handle);
+  /* 将 tray 的 icon 容器窗口起点放到 bar 中 x 这个位置 */
+  void (*place)(void *handle, int32_t x);
+  /* 设置 icon 数量变化回调 */
+  void (*set_listener)(
+    void *handle,
+    tray_icons_change_cb_t cb,
+    void *user_data
+  );
+} tray_api_t;
+
+typedef struct tray_t {
+  tray_api_t api;
+  void *handle;
+} tray_t;

src/runtime/runtime.c

@@ -1,6 +1,5 @@
 #include "runtime/runtime.h"
 
-#include <bits/types/sigset_t.h>
 #include <dlfcn.h>
 #include <signal.h>
 #include <stddef.h>
@@ -121,7 +120,10 @@ static void runtime_init_bar(runtime_t *runtime) {
       .height = bar_height,
     };
     auto color = bar->palette.bg.argb;
-    auto bar_window = backend_create_bar_window(backend, bar_rect, color);
+    bool enable_tray = (int32_t)i == bar->config.tray_output_index;
+    auto bar_window =
+      backend_create_bar_window(backend, bar_rect, color, enable_tray);
+    bar->tray = bar_window.tray;
     auto bar_output = &bar->bars[i];
     bar_output->cr = bar_window.cr;
     bar_output->window_id = bar_window.window_id;