[#89] [#113] [#124] Focus improvements on dual and tripple cameras

README.md

@@ -35,6 +35,7 @@ You can provide a variety of extra customization options to `CodeScannerView` in
 - `showViewfinder` determines whether to show a box-like viewfinder over the UI. Default: false.
 - `simulatedData` allows you to provide some test data to use in Simulator, when real scanning isn’t available. Default: an empty string.
 - `shouldVibrateOnSuccess` allows you to determine whether device should vibrate when a code is found. Default: true.
+- `videoCaptureDevice` allows you to choose different capture device that is most suitable for code to scan. 
 
 If you want to add UI customization, such as a dedicated Cancel button, you should wrap your `CodeScannerView` instance in a `NavigationView` and use a `toolbar()` modifier to add whatever buttons you want.
 
@@ -87,6 +88,24 @@ struct QRCodeScannerExampleView: View {
 }
 ```
 
+## Scanning small QR codes
+
+Scanning small QR code on devices with dual or tripple cameras has to be adjusted because of minimum focus distance built in these cameras.
+To have the best possible focus on the code we scan it is needed to choose the most suitable camera and apply recommended zoom factor.
+
+Example for scanning 20x20mm QR codes.
+
+```swift
+CodeScannerView(codeTypes: [.qr], videoCaptureDevice: AVCaptureDevice.zoomedCameraForQRCode(withMinimumCodeSize: 20)) { response in                    
+    switch response {
+    case .success(let result):
+        print("Found code: \(result.string)")
+    case .failure(let error):
+        print(error.localizedDescription)
+    }
+}
+```
+
 
 ## Credits
 

Sources/CodeScanner/AVCaptureDevice+bestForBuiltInCamera.swift

@@ -0,0 +1,125 @@
+//
+//  AVCaptureDevice+bestForBuiltInCamera.swift
+//  https://github.com/twostraws/CodeScanner
+//
+//  Created by Karol Bielski on 10/02/2024.
+//  Copyright © 2024 Paul Hudson. All rights reserved.
+//
+
+import AVFoundation
+
+@available(macCatalyst 14.0, *)
+extension AVCaptureDevice {
+
+    /// Returns best built in back camera for scanning QR codes zoomed for a given minimum code size.
+    static func zoomedCameraForQRCode(withMinimumCodeSize minimumCodeSize: Float = 20) -> AVCaptureDevice? {
+        let captureDevice = AVCaptureDevice.DiscoverySession(
+            deviceTypes: [.builtInWideAngleCamera],
+            mediaType: .video,
+            position: .back
+        ).devices.first ?? AVCaptureDevice.default(for: .video)
+
+        if #available(iOS 15.0, *) {
+            captureDevice?.setRecommendedZoomFactor(forMinimumCodeSize: minimumCodeSize)
+        }
+
+        return captureDevice
+    }
+
+    /// Sets recommended zoom factor for a given minimum code size.
+    @available(iOS 15.0, *)
+    func setRecommendedZoomFactor(forMinimumCodeSize minimumCodeSize: Float) {
+        /*
+         Optimize the user experience for scanning QR codes down to given size.
+         When scanning a QR code of that size, the user may need to get closer than
+         the camera's minimum focus distance to fill the rect of interest.
+         To have the QR code both fill the rect and still be in focus, we may need to apply some zoom.
+         */
+        let deviceMinimumFocusDistance = Float(minimumFocusDistance)
+        guard deviceMinimumFocusDistance != -1 else { return }
+
+        let deviceFieldOfView = activeFormat.videoFieldOfView
+        let formatDimensions = CMVideoFormatDescriptionGetDimensions(activeFormat.formatDescription)
+        let rectOfInterestWidth = Double(formatDimensions.height) / Double(formatDimensions.width)
+        let minimumSubjectDistanceForCode = minimumSubjectDistanceForCode(
+            fieldOfView: deviceFieldOfView,
+            minimumCodeSize: minimumCodeSize,
+            previewFillPercentage: Float(rectOfInterestWidth)
+        )
+
+        guard minimumSubjectDistanceForCode < deviceMinimumFocusDistance else { return }
+
+        let zoomFactor = deviceMinimumFocusDistance / minimumSubjectDistanceForCode
+        do {
+            try lockForConfiguration()
+            videoZoomFactor = CGFloat(zoomFactor)
+            unlockForConfiguration()
+        } catch {
+            print("Could not lock for configuration: \(error)")
+        }
+    }
+
+    private func minimumSubjectDistanceForCode(
+        fieldOfView: Float,
+        minimumCodeSize: Float,
+        previewFillPercentage: Float
+    ) -> Float {
+        /*
+         Given the camera horizontal field of view, we can compute the distance (mm) to make a code
+         of minimumCodeSize (mm) fill the previewFillPercentage.
+         */
+        let radians = (fieldOfView / 2).radians
+        let filledCodeSize = minimumCodeSize / previewFillPercentage
+        return filledCodeSize / tan(radians)
+    }
+}
+
+private extension Float {
+    var radians: Float {
+        self * Float.pi / 180
+    }
+}
+
+/*
+ Part of this code is copied from Apple sample project "AVCamBarcode: Using AVFoundation to capture barcodes".
+
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