public Rect scalePreview(Size previewSize) {
        return previewScalingStrategy.scalePreview(previewSize, viewfinderSize);
    }
Scale the preview to cover the viewfinder, then center it.

Aspect ratio is preserved.

@param previewSize the size of the preview (camera), in current display orientation
@return a rect placing the preview
zxing-android-embedded/src/com/journeyapps/barcodescanner/camera/DisplayConfiguration.java