Display camera frame

part/part.go

@@ -0,0 +1,87 @@
+package part
+
+import (
+	"fmt"
+	mqtt "github.com/eclipse/paho.mqtt.golang"
+	"gocv.io/x/gocv"
+	"log"
+	"time"
+)
+
+func NewPart(client mqtt.Client, frameTopic string) *FramePart {
+	return &FramePart{
+		client:     client,
+		frameTopic: frameTopic,
+		window:     gocv.NewWindow(frameTopic),
+		img:        gocv.NewMat(),
+	}
+
+}
+
+type FramePart struct {
+	client     mqtt.Client
+	frameTopic string
+	window     *gocv.Window
+	img        gocv.Mat
+}
+
+func (p *FramePart) Start() error {
+	if err := p.registerCallbacks(); err != nil {
+		return fmt.Errorf("unable to start service: %v", err)
+	}
+	for {
+		time.Sleep(1 * time.Hour)
+	}
+}
+
+func (p *FramePart) Stop() {
+	defer func (){
+		err := p.img.Close()
+		if err != nil {
+			log.Printf("unable to close resource: %v", err)
+		}
+	}()
+	defer p.window.Close()
+	StopService("frame-display", p.client, p.frameTopic)
+}
+
+func (p *FramePart) onFrame(_ mqtt.Client, message mqtt.Message) {
+		img, err := gocv.IMDecode(message.Payload(), gocv.IMReadUnchanged)
+		if err != nil {
+			log.Printf("unable to decode image: %v", err)
+			return
+		}
+		defer img.Close()
+		img.CopyTo(&p.img)
+		p.window.IMShow(p.img)
+		p.window.WaitKey(1)
+}
+
+func (p *FramePart) registerCallbacks() error {
+	err := RegisterCallback(p.client, p.frameTopic, p.onFrame)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func StopService(name string, client mqtt.Client, topics ...string) {
+	log.Printf("Stop %s service", name)
+	token := client.Unsubscribe(topics...)
+	token.Wait()
+	if token.Error() != nil {
+		log.Printf("unable to unsubscribe service: %v", token.Error())
+	}
+	client.Disconnect(50)
+}
+
+func RegisterCallback(client mqtt.Client, topic string, callback mqtt.MessageHandler) error {
+	log.Printf("Register callback on topic %v", topic)
+	token := client.Subscribe(topic, 0, callback)
+	token.Wait()
+	if token.Error() != nil {
+		return fmt.Errorf("unable to register callback on topic %s: %v", topic, token.Error())
+	}
+	return nil
+}