title: React-native-camera limit barcode scan area
body: <p>I am using the barcode scanner from <a href="https://github.com/react-native-community/react-native-camera" rel="noreferrer">react-native-camera</a> and currently if I use it and there are multiple QR-codes closely on top of each other, I point my camera at one and it reads the code above it which is outside of the display on screen but within the cameras view. If however there is no QR-code above the one I want to scan, then it scans the correct one, so it seems like it always scans the top QR-code within the cameras view.</p>
  
  <p><strong>Here's my question:</strong> Is there a way to limit the "scan area" to be the same size and area as my camera view on my display?</p>
  
  <pre><code>&lt;View style={styles.container}&gt;
    &lt;Camera
      style={styles.preview}
      onBarCodeRead={this.onBarCodeRead}
      ref={cam =&gt; this.camera = cam}
      aspect={Camera.constants.Aspect.fill}&gt;
    &lt;/Camera&gt;
    &lt;Button
      style={styles.buttonStyle}
      &lt;Text&gt;{this.state.qrcode}&lt;/Text&gt;
    &lt;/Button&gt;
  &lt;/View&gt;
  
  const styles = {
    container: {
      height: 300,
      flex: 1
    },
    preview: {
      flex: 1
    },
    buttonStyle: {
      marginTop: 20,
      marginLeft: 20,
      marginRight: 20,
      marginBottom: 20,
      alignSelf: 'center'
    }
  }
  </code></pre>
  
  <p>Versions, if needed:</p>
  
  <pre><code>"react-native": "0.42.3",
  "react-native-camera": "0.6.0",
  </code></pre>