zxing: Code128 ResultPoints return incorrect values

Currently the Code128Reader reader is providing a Result information with incorrect coordinates at where the code starts and ends.

Taking the following barcode as an example:

I’m getting the following results:

{
    "text": "foobar\n",
    "rawBytes": "aEZPT0JBUmVKQWo=",
    "numBits": 88,
    "resultPoints": [
    {
        "x": 59,
        "y": 122
    },
    {
        "x": 499,
        "y": 122
    }],
    "resultMetadata": {
        "SYMBOLOGY_IDENTIFIER": "]C0"
    },
    "timestamp": 1656682389903,
    "barcodeFormat": "CODE_128"
}

Now the result point 1 is [59,122], which is in de middle of the Code128 start pattern, not the start of the actual data nor the start of the barcode.

Looking at decodeRow method Code128Reader, the startPatternInfo is found first and the code is decoded. This is all correct, however at the end where the result is constructed the left and right (which are the points returned in the result) are calculated based on the startPatternInfo.

In this case left is calculated as (startPatternInfo[1] + startPatternInfo[0]) / 2.0f; here the startPatternInfo[0] has the actual position (albeit 1 pixel off in the example) of the barcode left coordinate. Right is calculated as lastStart + lastPatternSize / 2.0f which is also incorrect, since it results in the middle of the CODE_STOP of the Code128.

The fix for the left is straightforward, either use startPatternInfo[0] or “calculate it” based on startPatternInfo[1] and startPatternInfo[2] (startPatternInfo[2] - startPatternInfo[1]) which results in the same value as startPatternInfo[0];

From debugging info the startPatternInfo has the following values:

startPatternInfo[0] = 37
startPatternInfo[1] = 84
startPatternInfo[2] = 101

The fix for right requires more investigation.