Better memory footprint and using a dispatch queue

By not passing in the buffer to the barcode detect and using an image instead the footprint of the memory usage is significantly reduced.

@@ -2,6 +2,7 @@ import AVFoundation
 import FlutterMacOS
 import Vision
 import AppKit
+import VideoToolbox
 
 public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler, FlutterTexture, AVCaptureVideoDataOutputSampleBufferDelegate {
     
@@ -17,7 +18,7 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
     var captureSession: AVCaptureSession!
     
     // The selected camera
-    var device: AVCaptureDevice!
+    weak var device: AVCaptureDevice!
 
     // Image to be sent to the texture
     var latestBuffer: CVImageBuffer!
@@ -95,7 +96,7 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
     }
     
     var nextScanTime = 0.0
-    var imagesCurrentlyBeingProcessed = 0
+    var imagesCurrentlyBeingProcessed = false
     
     // Gets called when a new image is added to the buffer
     public func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
@@ -111,45 +112,47 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
         registry.textureFrameAvailable(textureId)
         
         let currentTime = Date().timeIntervalSince1970
-        let eligibleForScan = currentTime > nextScanTime && imagesCurrentlyBeingProcessed == 0;
+        let eligibleForScan = currentTime > nextScanTime && imagesCurrentlyBeingProcessed == false
         if ((detectionSpeed == DetectionSpeed.normal || detectionSpeed == DetectionSpeed.noDuplicates) && eligibleForScan || detectionSpeed == DetectionSpeed.unrestricted) {
             nextScanTime = currentTime + timeoutSeconds
-            imagesCurrentlyBeingProcessed += 1
-            let imageRequestHandler = VNImageRequestHandler(
-                cvPixelBuffer: latestBuffer,
-                orientation: .right)
-            
+            imagesCurrentlyBeingProcessed = true
+            DispatchQueue.global(qos: .userInitiated).async { [weak self] in
+                if(self!.latestBuffer == nil){
+                    return
+                }
+                var cgImage: CGImage?
+                VTCreateCGImageFromCVPixelBuffer(self!.latestBuffer, options: nil, imageOut: &cgImage)
+                let imageRequestHandler = VNImageRequestHandler(cgImage: cgImage!)
                 do {
-                  let barcodeRequest:VNDetectBarcodesRequest = VNDetectBarcodesRequest(completionHandler: { [self] (request, error) in
-                    imagesCurrentlyBeingProcessed -= 1
+                    let barcodeRequest:VNDetectBarcodesRequest = VNDetectBarcodesRequest(completionHandler: { [weak self] (request, error) in
+                        self?.imagesCurrentlyBeingProcessed = false
                         if error == nil {
                             if let results = request.results as? [VNBarcodeObservation] {
                                 for barcode in results {
-                                    if self.scanWindow != nil {
-                                        let match = self.isbarCodeInScanWindow(self.scanWindow!, barcode, self.latestBuffer)
-                                        if (!match) {
+                                    if self?.scanWindow != nil && cgImage != nil {
+                                        let match = self?.isbarCodeInScanWindow(self!.scanWindow!, barcode, cgImage!)
+                                        if (match == false) {
                                             continue
                                         }
                                     }
 
-                                    let barcodeType = String(barcode.symbology.rawValue).replacingOccurrences(of: "VNBarcodeSymbology", with: "")
-                                  let event: [String: Any?] = ["name": "barcodeMac", "data" : ["payload": barcode.payloadStringValue, "symbology": barcode.symbology.toInt as Any?]]
-                                    self.sink?(event)
-
-        //                                    if barcodeType == "QR" {
-        //                                        let image = CIImage(image: source)
-        //                                        image?.cropping(to: barcode.boundingBox)
-        //                                        self.qrCodeDescriptor(qrCode: barcode, qrCodeImage: image!)
-        //                                    }
+                                    DispatchQueue.main.async {
+                                        self?.sink?(["name": "barcodeMac", "data" : ["payload": barcode.payloadStringValue, "symbology": barcode.symbology.toInt as Any?]] as [String : Any])
+                                    }
+//                                   if barcodeType == "QR" {
+//                                        let image = CIImage(image: source)
+//                                        image?.cropping(to: barcode.boundingBox)
+//                                        self.qrCodeDescriptor(qrCode: barcode, qrCodeImage: image!)
+//                                    }
                                 }
                             }
                         } else {
                             print(error!.localizedDescription)
                         }
                     })
-                  if(symbologies.isEmpty == false){
+                    if(self?.symbologies.isEmpty == false){
                         // add the symbologies the user wishes to support
-                    barcodeRequest.symbologies = symbologies
+                        barcodeRequest.symbologies = self!.symbologies
                     }
                     try imageRequestHandler.perform([barcodeRequest])
                 } catch {
@@ -157,6 +160,7 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
                 }
             }
         }
+    }
     
     func checkPermission(_ call: FlutterMethodCall, _ result: @escaping FlutterResult) {
         if #available(macOS 10.14, *) {
@@ -199,6 +203,20 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
         scanWindow = CGRect(x: minX, y: minY, width: width, height: height)
     }
     
+    func isbarCodeInScanWindow(_ scanWindow: CGRect, _ barcode: VNBarcodeObservation, _ inputImage: CGImage) -> Bool {
+
+        let imageWidth = CGFloat(inputImage.width);
+        let imageHeight = CGFloat(inputImage.height);
+
+        let minX = scanWindow.minX * imageWidth
+        let minY = scanWindow.minY * imageHeight
+        let width = scanWindow.width * imageWidth
+        let height = scanWindow.height * imageHeight
+
+        let scaledScanWindow = CGRect(x: minX, y: minY, width: width, height: height)
+        return scaledScanWindow.contains(barcode.boundingBox)
+    }
+
     func isbarCodeInScanWindow(_ scanWindow: CGRect, _ barcode: VNBarcodeObservation, _ inputImage: CVImageBuffer) -> Bool {
         let size = CVImageBufferGetEncodedSize(inputImage)
 
@@ -227,11 +245,11 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
 
         let argReader = MapArgumentReader(call.arguments as? [String: Any])
 
-//        let ratio: Int = argReader.int(key: "ratio")
-        let torch: Bool = argReader.bool(key: "torch") ?? false
-        let facing: Int = argReader.int(key: "facing") ?? 1
-        let speed: Int = (call.arguments as! Dictionary<String, Any?>)["speed"] as? Int ?? 0
-        let timeoutMs: Int = (call.arguments as! Dictionary<String, Any?>)["timeout"] as? Int ?? 0
+        // let ratio: Int = argReader.int(key: "ratio")
+        let torch:Bool = argReader.bool(key: "torch") ?? false
+        let facing:Int = argReader.int(key: "facing") ?? 1
+        let speed:Int = argReader.int(key: "speed") ?? 0
+        let timeoutMs:Int = argReader.int(key: "timeout") ?? 0
         symbologies = argReader.toSymbology()
 
         timeoutSeconds = Double(timeoutMs) / 1000.0
@@ -285,7 +303,7 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
         videoOutput.setSampleBufferDelegate(self, queue: DispatchQueue.main)
         captureSession.addOutput(videoOutput)
         for connection in videoOutput.connections {
-//            connection.videoOrientation = .portrait
+            // connection.videoOrientation = .portrait
             if position == .front && connection.isVideoMirroringSupported {
                 connection.isVideoMirrored = true
             }
@@ -472,5 +490,4 @@ extension VNBarcodeSymbology {
             return -1;
         }
     }
-  
 }