Suppress PICTURE broadcast when nobody is listening

pkg/controller/picture.go

@@ -18,6 +18,10 @@ func (c *controller) HandlePicture(request *brevity.PictureRequest) {
 }
 
 func (c *controller) broadcastPicture(logger *zerolog.Logger, forceBroadcast bool) {
+	if c.srsClient.ClientsOnFrequency() == 0 && !forceBroadcast {
+		logger.Debug().Msg("skipping PICTURE broadcast because no clients are on frequency")
+		return
+	}
 	count, groups := c.scope.GetPicture(conf.DefaultPictureRadius, c.coalition.Opposite(), brevity.FixedWing)
 	isPictureClean := count == 0
 	for _, group := range groups {

pkg/simpleradio/client.go

@@ -29,6 +29,8 @@ type Client interface {
 	Transmit(audio.Audio)
 	// IsOnFrequency checks if the named unit is on the client's frequency.
 	IsOnFrequency(string) bool
+	// ClientsOnFrequency returns the number of peers on this client's frequency.
+	ClientsOnFrequency() int
 }
 
 // client implements the SRS Client.
@@ -132,3 +134,8 @@ func (c *client) Transmit(sample audio.Audio) {
 func (c *client) IsOnFrequency(name string) bool {
 	return c.dataClient.IsOnFrequency(name)
 }
+
+// ClientsOnFrequency implements [Client.ClientsOnFrequency].
+func (c *client) ClientsOnFrequency() int {
+	return c.dataClient.ClientsOnFrequency()
+}

pkg/simpleradio/data/client.go

@@ -28,6 +28,8 @@ type DataClient interface {
 	Send(types.Message) error
 	// IsOnFrequency checks if the named unit is on the client's frequency.
 	IsOnFrequency(string) bool
+	// ClientsOnFrequency returns the number of peers on this client's frequency.
+	ClientsOnFrequency() int
 }
 
 type dataClient struct {
@@ -322,3 +324,15 @@ func (c *dataClient) IsOnFrequency(name string) bool {
 	}
 	return false
 }
+
+func (c *dataClient) ClientsOnFrequency() int {
+	c.clientsLock.RLock()
+	defer c.clientsLock.RUnlock()
+	count := 0
+	for _, client := range c.clients {
+		if ok := c.clientInfo.RadioInfo.IsOnFrequency(client.RadioInfo); ok {
+			count++
+		}
+	}
+	return count
+}