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Works in portrait and landscape orientation, can read inverted codes, is Material Design and doesn't do anything else but decoding a barcode.
Uses the ZXing ("Zebra Crossing") barcode scanning library. Supported barcode formats are: AZTEC, CODABAR, CODE 39, CODE 93, CODE 128, DATA MATRIX, EAN 8, EAN 13, ITF, MAXICODE, PDF417, QR CODE, RSS 14, RSS EXPANDED, UPC A, UPC E and UPC EAN EXTENSION.
This is open source: