backlight: add DDC/CI support for external monitors

meson_options.txt

 option('systemd-service', type: 'boolean', value: true, description: 'Install systemd user service unit.')
 option('scripting', type: 'boolean', value: true, description: 'Enable notification scripting.')
 option('pulse-audio', type: 'boolean', value: true, description: 'Provide PulseAudio Widget.')
+option('ddc', type: 'boolean', value: true, description: 'Provide DDC/CI monitor brightness control via libddcutil.')
 option('man-pages', type: 'boolean', value: true, description: 'Install all man pages.')
 option('zsh-completions', type: 'boolean', value: true, description: 'Install zsh shell completions.')
 option('bash-completions', type: 'boolean', value: true, description: 'Install bash shell completions.')

src/configSchema.json

@@ -794,14 +794,19 @@
         },
         "subsystem": {
           "type": "string",
-          "description": "Kernel subsystem for brightness control",
+          "description": "Kernel subsystem for brightness control. Use 'ddc' for external monitors via DDC/CI (requires build with -Dddc=true).",
           "default": "backlight",
-          "enum": ["backlight", "leds"]
+          "enum": ["backlight", "leds", "ddc"]
         },
         "min": {
           "type": "integer",
           "default": 0,
           "description": "Lowest possible value for brightness"
+        },
+        "display-number": {
+          "type": "integer",
+          "default": 0,
+          "description": "DDC display number (from ddcutil detect). 0 means first available. Only used with subsystem 'ddc'."
         }
       }
     },

src/controlCenter/widgets/backlight/backlight.vala

@@ -9,6 +9,10 @@ namespace SwayNotificationCenter.Widgets {
         }
 
         BacklightUtil client;
+#if HAVE_DDC
+        DdcUtil[] ddc_clients = {};
+        bool use_ddc = false;
+#endif
 
         Gtk.Label label_widget = new Gtk.Label (null);
         Gtk.Scale slider = new Gtk.Scale.with_range (Gtk.Orientation.HORIZONTAL, 0, 100, 1);
@@ -27,9 +31,17 @@ namespace SwayNotificationCenter.Widgets {
                 switch (subsystem) {
                     default :
                     case "backlight":
-                        if (subsystem != "backlight") {
+                        if (subsystem != "backlight"
+#if HAVE_DDC
+                            && subsystem != "ddc"
+#endif
+                        ) {
                             info ("Invalid subsystem %s for device %s. " +
-                                  "Use 'backlight' or 'leds'. Using default: 'backlight'",
+                                  "Use 'backlight', 'leds'" +
+#if HAVE_DDC
+                                  ", 'ddc'" +
+#endif
+                                  ". Using default: 'backlight'",
                                   subsystem, device);
                         }
                         client = new BacklightUtil ("backlight", device);
@@ -39,8 +51,89 @@ namespace SwayNotificationCenter.Widgets {
                         client = new BacklightUtil ("leds", device);
                         slider.set_range (min, this.client.get_max_value ());
                         break;
+#if HAVE_DDC
+                    case "ddc":
+                        int display_number = int.max (0, get_prop<int> (config, "display-number"));
+                        use_ddc = true;
+
+                        if (display_number > 0) {
+                            ddc_clients += new DdcUtil (display_number);
+                            slider.set_range (min, 100);
+                        } else {
+                            // Auto-detect all DDC displays
+                            var displays = DdcUtil.detect_displays ();
+                            if (displays.length == 0) {
+                                warning ("No DDC displays found");
+                                hide ();
+                                return;
+                            }
+                            for (int i = 0; i < displays.length; i++) {
+                                var ddc = new DdcUtil (displays[i].dispno);
+                                ddc_clients += ddc;
+                            }
+                        }
+                        break;
+#endif
+                }
+            }
+
+#if HAVE_DDC
+            if (use_ddc) {
+                if (ddc_clients.length == 1) {
+                    // Single DDC display — use the existing label + slider
+                    if (label_widget.get_label () == "Brightness") {
+                        label_widget.set_label ("󰍹");
+                        label_widget.set_tooltip_text (ddc_clients[0].get_display_name ());
+                    }
+                    ddc_clients[0].brightness_change.connect ((percent) => {
+                        if (percent < 0) {
+                            hide ();
+                        } else {
+                            slider.set_value (percent);
+                        }
+                    });
+                    slider.set_draw_value (false);
+                    slider.set_round_digits (0);
+                    slider.set_hexpand (true);
+                    slider.value_changed.connect (() => {
+                        ddc_clients[0].set_brightness.begin ((float) slider.get_value ());
+                        slider.tooltip_text = ((int) slider.get_value ()).to_string ();
+                    });
+                    append (label_widget);
+                    append (slider);
+                } else {
+                    // Multiple DDC displays — create a row per display
+                    set_orientation (Gtk.Orientation.VERTICAL);
+                    for (int i = 0; i < ddc_clients.length; i++) {
+                        var row = new Gtk.Box (Gtk.Orientation.HORIZONTAL, 0);
+                        var lbl = new Gtk.Label ("󰍹 %d".printf (i + 1));
+                        lbl.set_tooltip_text (ddc_clients[i].get_display_name ());
+                        var scl = new Gtk.Scale.with_range (Gtk.Orientation.HORIZONTAL, 0, 100, 1);
+                        scl.set_draw_value (false);
+                        scl.set_round_digits (0);
+                        scl.set_hexpand (true);
+
+                        int idx = i;
+                        ddc_clients[i].brightness_change.connect ((percent) => {
+                            if (percent < 0) {
+                                row.hide ();
+                            } else {
+                                scl.set_value (percent);
+                            }
+                        });
+                        scl.value_changed.connect (() => {
+                            ddc_clients[idx].set_brightness.begin ((float) scl.get_value ());
+                            scl.tooltip_text = ((int) scl.get_value ()).to_string ();
+                        });
+
+                        row.append (lbl);
+                        row.append (scl);
+                        append (row);
+                    }
                 }
+                return;
             }
+#endif
 
             this.client.brightness_change.connect ((percent) => {
                 if (percent < 0) { // invalid device path
@@ -63,6 +156,18 @@ namespace SwayNotificationCenter.Widgets {
         }
 
         public override void on_cc_visibility_change (bool val) {
+#if HAVE_DDC
+            if (use_ddc) {
+                foreach (var ddc in ddc_clients) {
+                    if (val) {
+                        ddc.start ();
+                    } else {
+                        ddc.close ();
+                    }
+                }
+                return;
+            }
+#endif
             if (val) {
                 this.client.start ();
             } else {

src/controlCenter/widgets/backlight/ddcUtil.vala

+namespace SwayNotificationCenter.Widgets {
+
+    public struct DdcDisplayInfo {
+        int dispno;
+        string model_name;
+    }
+
+    class DdcUtil {
+        const uint8 VCP_BRIGHTNESS = 0x10;
+
+        void* handle = null;
+        string display_name = "DDC Display";
+
+        static bool lib_initialized = false;
+
+        uint poll_source = 0;
+
+        public signal void brightness_change (int percent);
+
+        public DdcUtil (int display_number) {
+            if (!init_library ()) return;
+            open_display (display_number);
+        }
+
+        private static bool init_library () {
+            if (lib_initialized) return true;
+
+            string[]? msgs;
+            int rc = Ddcutil.init2 (
+                null,
+                Ddcutil.SyslogLevel.NEVER,
+                Ddcutil.InitOptions.DISABLE_CONFIG_FILE,
+                out msgs);
+
+            if (rc != 0) {
+                warning ("ddcutil init failed: %d", rc);
+                return false;
+            }
+            lib_initialized = true;
+            return true;
+        }
+
+        public static DdcDisplayInfo[] detect_displays () {
+            if (!init_library ()) return {};
+
+            Ddcutil.DisplayInfoList? dlist;
+            int rc = Ddcutil.get_display_info_list2 (false, out dlist);
+            if (rc != 0 || dlist == null || dlist.ct == 0) {
+                return {};
+            }
+
+            DdcDisplayInfo[] result = {};
+            for (int i = 0; i < dlist.ct; i++) {
+                result += DdcDisplayInfo () {
+                    dispno = dlist.info[i].dispno,
+                    model_name = ((string) dlist.info[i].model_name).dup (),
+                };
+            }
+            return result;
+        }
+
+        private void open_display (int display_number) {
+            Ddcutil.DisplayInfoList? dlist;
+            int rc = Ddcutil.get_display_info_list2 (false, out dlist);
+            if (rc != 0 || dlist == null || dlist.ct == 0) {
+                warning ("No DDC displays found");
+                brightness_change (-1);
+                return;
+            }
+
+            int idx = 0;
+            if (display_number > 0) {
+                bool found = false;
+                for (int i = 0; i < dlist.ct; i++) {
+                    if (dlist.info[i].dispno == display_number) {
+                        idx = i;
+                        found = true;
+                        break;
+                    }
+                }
+                if (!found) {
+                    warning ("DDC display %d not found, using first", display_number);
+                }
+            }
+
+            display_name = ((string) dlist.info[idx].model_name).dup ();
+
+            void* dh;
+            rc = Ddcutil.open_display2 (dlist.info[idx].dref, true, out dh);
+            if (rc != 0) {
+                warning ("Failed to open DDC display: %d", rc);
+                brightness_change (-1);
+                return;
+            }
+            handle = dh;
+        }
+
+        public void start () {
+            get_brightness ();
+            start_polling ();
+        }
+
+        public void close () {
+            stop_polling ();
+        }
+
+        private void start_polling () {
+            stop_polling ();
+            poll_source = Timeout.add_seconds (5, () => {
+                get_brightness ();
+                return Source.CONTINUE;
+            });
+        }
+
+        private void stop_polling () {
+            if (poll_source != 0) {
+                Source.remove (poll_source);
+                poll_source = 0;
+            }
+        }
+
+        private void get_brightness () {
+            if (handle == null) {
+                brightness_change (-1);
+                return;
+            }
+
+            Ddcutil.NonTableVcpValue val;
+            int rc = Ddcutil.get_non_table_vcp_value (handle, VCP_BRIGHTNESS, out val);
+
+            if (rc != 0) {
+                warning ("Failed to read DDC brightness: %d", rc);
+                return;
+            }
+
+            int current = (val.sh << 8) | val.sl;
+            int max = (val.mh << 8) | val.ml;
+
+            if (max == 0) {
+                brightness_change (-1);
+                return;
+            }
+
+            int percent = (int) Math.round (current * 100.0 / max);
+            brightness_change (percent);
+        }
+
+        public async void set_brightness (float percent) {
+            if (handle == null) return;
+
+            int value = (int) Math.round (percent);
+            if (value < 0) value = 0;
+            if (value > 100) value = 100;
+
+            int rc = Ddcutil.set_non_table_vcp_value (handle, VCP_BRIGHTNESS, 0, (uint8) value);
+
+            if (rc != 0) {
+                warning ("Failed to set DDC brightness: %d", rc);
+            }
+        }
+
+        public string get_display_name () {
+            return display_name;
+        }
+
+        ~DdcUtil () {
+            stop_polling ();
+            if (handle != null) {
+                Ddcutil.close_display (handle);
+                handle = null;
+            }
+        }
+    }
+}

src/controlCenter/widgets/backlight/ddcutil.vapi

+[CCode (cheader_filename = "ddcutil_c_api.h")]
+namespace Ddcutil {
+
+    [CCode (cname = "DDCA_Syslog_Level", cprefix = "DDCA_SYSLOG_")]
+    public enum SyslogLevel {
+        [CCode (cname = "DDCA_SYSLOG_NOT_SET")]
+        NOT_SET,
+        [CCode (cname = "DDCA_SYSLOG_NEVER")]
+        NEVER
+    }
+
+    [CCode (cname = "DDCA_Init_Options", cprefix = "DDCA_INIT_OPTIONS_")]
+    [Flags]
+    public enum InitOptions {
+        [CCode (cname = "DDCA_INIT_OPTIONS_NONE")]
+        NONE,
+        [CCode (cname = "DDCA_INIT_OPTIONS_DISABLE_CONFIG_FILE")]
+        DISABLE_CONFIG_FILE
+    }
+
+    [CCode (cname = "DDCA_Non_Table_Vcp_Value", has_type_id = false)]
+    public struct NonTableVcpValue {
+        public uint8 mh;
+        public uint8 ml;
+        public uint8 sh;
+        public uint8 sl;
+    }
+
+    // All fields must be present to match C struct layout
+    [CCode (cname = "DDCA_Display_Info", has_type_id = false, destroy_function = "")]
+    public struct DisplayInfo {
+        public char marker[4];
+        public int dispno;
+        [CCode (cname = "path")]
+        public uint8 _path[8];
+        public int usb_bus;
+        public int usb_device;
+        public char mfg_id[4];
+        public char model_name[14];
+        public char sn[14];
+        public uint16 product_code;
+        public uint8 edid_bytes[128];
+        [CCode (cname = "vcp_version")]
+        public uint8 _vcp_version[2];
+        [CCode (cname = "dref")]
+        public void* dref;
+    }
+
+    [CCode (cname = "DDCA_Display_Info_List", has_type_id = false,
+            free_function = "ddca_free_display_info_list")]
+    [Compact]
+    public class DisplayInfoList {
+        public int ct;
+        [CCode (cname = "info", array_length_cname = "ct")]
+        public DisplayInfo info[0];
+    }
+
+    [CCode (cname = "ddca_init2")]
+    public static int init2 (
+        string? libopts,
+        SyslogLevel syslog_level,
+        InitOptions opts,
+        [CCode (array_length = false)]
+        out string[]? infomsg);
+
+    [CCode (cname = "ddca_get_display_info_list2")]
+    public static int get_display_info_list2 (
+        bool include_invalid,
+        out DisplayInfoList? dlist);
+
+    [CCode (cname = "ddca_open_display2")]
+    public static int open_display2 (
+        void* dref,
+        bool wait,
+        out void* dh);
+
+    [CCode (cname = "ddca_close_display")]
+    public static int close_display (void* dh);
+
+    [CCode (cname = "ddca_get_non_table_vcp_value")]
+    public static int get_non_table_vcp_value (
+        void* dh,
+        uint8 feature_code,
+        out NonTableVcpValue valrec);
+
+    [CCode (cname = "ddca_set_non_table_vcp_value")]
+    public static int set_non_table_vcp_value (
+        void* dh,
+        uint8 feature_code,
+        uint8 hi_byte,
+        uint8 lo_byte);
+}

src/meson.build

@@ -120,6 +120,19 @@ if get_option('pulse-audio')
   ]
 endif
 
+# Checks if the user wants to compile with DDC/CI support
+if get_option('ddc')
+  add_project_arguments('-D', 'HAVE_DDC', language: 'vala')
+  ddcutil_vapi_dir = meson.current_source_dir() / 'controlCenter' / 'widgets' / 'backlight'
+  app_deps += [
+    cc.find_library('ddcutil', required: true),
+    vala.find_library('ddcutil', dirs: ddcutil_vapi_dir),
+  ]
+  app_sources += [
+    'controlCenter/widgets/backlight/ddcUtil.vala',
+  ]
+endif
+
 args = [
   '--target-glib=2.82',
 ]