Patch for ngx scanner, only center areas are valid for scanning.

ngx-scanner-center-scan-patch.js

// Patch for node_modules/@zxing/ngx-scanner/esm5/zxing-ngx-scanner.js
BrowserCodeReader.prototype.createBinaryBitmap = function (mediaElement) {
        if (undefined === this.canvasElementContext) {
            this.prepareCaptureCanvas();
        }
        this.canvasElementContext.drawImage(mediaElement, 0, 0);
        // FIXME byHo
        // var luminanceSource = new HTMLCanvasElementLuminanceSource(this.canvasElement);
        // var hybridBinarizer = new HybridBinarizer(luminanceSource);
        // return new BinaryBitmap(hybridBinarizer);
        
        const allWidth = this.canvasElement.width;
        const allHeight = this.canvasElement.height;
        const left = allWidth/4;
        const top = Math.min(allWidth, allHeight)/4;
        const squareSize = Math.min(allWidth, allHeight) / 2;
        // const crop = all.crop(left, top, squareSize, squareSize);

        var canvas1 = document.createElement("canvas");
        canvas1.width = squareSize;
        canvas1.height = squareSize;
        var ctx1 = canvas1.getContext("2d");
        ctx1.rect(0, 0, squareSize, squareSize);
        ctx1.fillStyle = 'white';
        ctx1.fill();
        // ctx1.putImageData(crop.binarizer.source, 0, 0);
        ctx1.putImageData(
            this.canvasElementContext.getImageData(left, top, squareSize, squareSize), 
            0, 0);

        $('.dstImg').attr('src', canvas1.toDataURL("image/png"));
        // $('.dstImg').each((i, img) => 
        //     this.canvasElementContext.drawImage(img, left, top, squareSize, squareSize, 0, 0, squareSize, squareSize));

        var luminanceSource = new HTMLCanvasElementLuminanceSource(canvas1);
        var hybridBinarizer = new HybridBinarizer(luminanceSource);

        // hybridBinarizer.source.buffer = crop.binarizer.source;
        // hybridBinarizer.source.width = squareSize;
        // hybridBinarizer.source.height = squareSize;
        return new BinaryBitmap(hybridBinarizer);
    };

请问这个怎么使用，把你的这段代码拷贝到 node_modules/@zxing/ngx-scanner/esm5/zxing-ngx-scanner.js 里面吗？
效果是会在全屏相机区域中选定一部分区域吗， 就像微信扫码那样？