[Instruments] WaveformFormat.RIGOL_WORD value accessor reads bytes, not 16-bit words — WORD waveforms render garbage

[ammaree]

Summary

initValuesAccesor() in packages/eez-studio-ui/chart/value-accesor.ts
handles WaveformFormat.RIGOL_WORD with a correct length calculation but
a byte-oriented data accessor, so any waveform stored in RIGOL WORD
format renders as garbage (the first half of the buffer interpreted as
8-bit samples).

The code

} else if (format === WaveformFormat.RIGOL_WORD) {
    length = Math.floor(values.length / 2);   // correct: 2 bytes per point
    waveformData = (index: number) => {
        return values[index];                  // BUG: reads ONE byte at `index`,
    };                                         // not a 16-bit word at 2*index
    value = (index: number) => {
        return offset + waveformData(index) * scale;
    };
}

Compare RIGOL_BYTE directly above it — the accessor body is identical.
For WORD it should assemble two bytes per point, e.g. (little-endian):

waveformData = (index: number) => {
    return values[2 * index] | (values[2 * index + 1] << 8);
};

Why it matters

Rigol's current 12-bit scope generations (DHO800/DHO900/MHO900) only
deliver their full resolution via :WAVeform:FORMat WORD — BYTE
transfers quantize to 8 bits. Extension scripts that try to store
12-bit-faithful waveforms with session.addChart({format: RIGOL_WORD})
get corrupted rendering, and currently have to work around it by
converting to FLOATS in script (doubling memory).

Found while building IEXT extensions for the Rigol MHO98 / DHO924S
(12-bit). Related context: none of the official extensions appear to use
RIGOL_WORD (the official Rigol family scripts use BYTE), which is
presumably why this hasn't surfaced before.

Environment

• EEZ Studio 0.29.0 (code present on master at time of filing)

[mvladic]

Fixed. Thanks!

[ammaree]

Verified the fix against the commit — works as intended. Happy for this to be closed whenever suits you. Thanks for the quick turnaround.