Turn off MS-FonVal: The device table's DeltaFormat value is invalid errors for variable fonts?

[eliheuer]

Noise from ms-fonval is causing my markdown output to exceed the length GitHub can display. Can we limit or turn off the MS-FonVal: The device table's DeltaFormat value is invalid errors for variable fonts?

Observed behaviour

* :fire: **FAIL** MS-FonVal: The device table's DeltaFormat value is invalid DETAILS: LookupList, Lookup[0], SubTable[0](PairPos, fmt 1), PairSet[2], PairValueRecord[22], Value1, XAdvDeviceTable, DeltaFormat = 32768
* :fire: **FAIL** MS-FonVal: The device table's DeltaFormat value is invalid DETAILS: LookupList, Lookup[0], SubTable[0](PairPos, fmt 1), PairSet[2], PairValueRecord[23], Value1, XAdvDeviceTable, DeltaFormat = 32768
* :fire: **FAIL** MS-FonVal: The device table's DeltaFormat value is invalid DETAILS: LookupList, Lookup[0], SubTable[0](PairPos, fmt 1), PairSet[2], PairValueRecord[24], Value1, XAdvDeviceTable, DeltaFormat = 32768
* :fire: **FAIL** MS-FonVal: The device table's DeltaFormat value is invalid DETAILS: LookupList, Lookup[0], SubTable[0](PairPos, fmt 1), PairSet[3], PairValueRecord[0], Value1, XAdvDeviceTable, DeltaFormat = 32768
* :fire: **FAIL** MS-FonVal: The device table's DeltaFormat value is invalid DETAILS: LookupList, Lookup[0], SubTable[0](PairPos, fmt 1), PairSet[3], PairValueRecord[1], Value1, XAdvDeviceTable, DeltaFormat = 32768
* :fire: **FAIL** MS-FonVal: The device table's DeltaFormat value is invalid DETAILS: LookupList, Lookup[0], SubTable[0](PairPos, fmt 1), PairSet[3], PairValueRecord[2], Value1, XAdvDeviceTable, DeltaFormat = 32768
* :fire: **FAIL** MS-FonVal: The device table's DeltaFormat value is invalid DETAILS: LookupList, Lookup[0], SubTable[0](PairPos, fmt 1), PairSet[3], PairValueRecord[3], Value1, XAdvDeviceTable, DeltaFormat = 32768
* :fire: **FAIL** MS-FonVal: The device table's DeltaFormat value is invalid DETAILS: LookupList, Lookup[0], SubTable[0](PairPos, fmt 1), PairSet[3], PairValueRecord[4], Value1, XAdvDeviceTable, DeltaFormat = 32768

Expected behaviour

Ok, I see this is a *VF.ttf file, don't worry about this.

[felipesanches]

I have just committed code yesteday that allows us to filter certain fontval checks when dealing with variable fonts. I can add this one to the black list as well.

I would like to silence checks that are too noisy. But I would also want to be sure the check is also not important. What's the meaning of this specific check?

[felipesanches]

DeltaFormat = 32768 (same as 0x8000) means VARIATION_INDEX, according to https://docs.microsoft.com/en-us/typography/opentype/spec/chapter2

The FontVal problem description for this check only mentions the other values as possible valid ones. So apparently this means FontVal implementation is not up-to-date with more recent versions of the spec and that's why these spurious FAILs are being emitted. That's good enough reason to mute it.

[eliheuer]

My understanding of this FAIL is simply that ms-fonval doesn't fully know how to deal with variable fonts, and this fail is a result of that. I could be wrong and would like to understand this fail better.

[felipesanches]

It fails to understand a new valid value from a more recent version of the opentype spec. I have the impression that a whole lot of fval checks may have this kind of problem.

[HinTak]

If it is not up to date, file an issue at Microsoft's issue tracker.

@davelab6

[HinTak]

Fixed in HinTak/Font-Validator@37b5e71

@eliheuer : please file an issue at the Microsoft issue tracker (not mine) next time. Nobody hear about these sort of issues, nobody fixes them. Thank you.

Cc: @davelab6

[eliheuer]

@HinTak Sure, will do. Is the preferred place to post issues https://github.com/Microsoft/Font-Validator/issues ?

[HinTak]

@eliheuer yes. I do watch that space. In this case it might be appropriate to add specific details to microsoft/Font-Validator#64 , instead of filing new. Either way, issues like these go there.