panel: add output selection

README.md

@@ -57,6 +57,16 @@ Supported panel types:
 panel, floating, islands
 ```
 
+Optional monitor filter:
+
+```json
+{
+  "output": ["DP-1", "HDMI-A-1"]
+}
+```
+
+An empty or missing `output` list leaves Waybar on its default outputs.
+
 ## Module Resolution
 
 The config stores logical module names. At generation time, the panel merges

data/config.json

 {
   "position": "top",
   "type": "panel",
+  "output": [],
   "modules_left": [
     "image#menu",
     "tray"
@@ -17,4 +18,4 @@
     "bluetooth",
     "custom/notification"
   ]
-}
\ No newline at end of file
+}

src/config.go

@@ -20,6 +20,7 @@ const (
 type Config struct {
 	Position      string   `json:"position"`
 	Type          string   `json:"type"`
+	Output        []string `json:"output"`
 	ModulesLeft   []string `json:"modules_left"`
 	ModulesCenter []string `json:"modules_center"`
 	ModulesRight  []string `json:"modules_right"`
@@ -76,6 +77,12 @@ func (c Config) Validate() error {
 		return fmt.Errorf("unsupported panel type %q", c.Type)
 	}
 
+	for _, output := range c.Output {
+		if strings.TrimSpace(output) == "" {
+			return errors.New("output name cannot be empty")
+		}
+	}
+
 	for _, name := range append(append([]string{}, c.ModulesLeft...), append(c.ModulesCenter, c.ModulesRight...)...) {
 		if strings.TrimSpace(name) == "" {
 			return errors.New("module name cannot be empty")

src/generate.go

@@ -30,6 +30,10 @@ func GenerateConfig(cfg Config, registry Registry) ([]byte, error) {
 		out["name"] = cfg.Type
 	}
 
+	if len(cfg.Output) > 0 {
+		out["output"] = cfg.Output
+	}
+
 	if cfg.Type == "floating" || cfg.Type == "islands" {
 		applyFloatingMargins(out, cfg.Position)
 	}