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Applying Metric or Optical Kerning

Participant ,
Nov 03, 2021 Nov 03, 2021

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Hello,

My plugin is able to apply kerning of a specific value to text, but I cannot see how to apply Metric or Optical kerning.

I did find the code below for optical kerning, but it contains a lot of magic numbers and I am unable to find any info about it in the SDK.

ClassID kernmethod = 79875;
InterfacePtr<IAttrReport> attr12(SnpTextAttrHelper::CreateTextAttribute<ITextAttrClassID, ITextAttrClassID::ValueType>(kTextAttrPairKernMethodBoss,kernmethod));
charAttributeBossList->ApplyAttribute(attr12);
SnpTextModelHelper	textCmdHelper;
status = textCmdHelper.ApplyOverrides(textModel, position, length, charAttributeBossList, kCharAttrStrandBoss);

 Does anyone know how to apply Metric or Optical kerning to text ?

Very best regards,

Olivier

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correct answers 1 Correct answer

Guide , Nov 04, 2021 Nov 04, 2021
Sorry, too much editing too late in the evening. "Metric". You're dealing with two attributes, kTextAttrPairKernBoss and kTextAttrPairKernMethodBoss Attribute kTextAttrPairKernBoss stores the numeric value in its IID_ITEXTATTRREALNUMBER; limits are -2.000000..10.000000 for regular values, otherwise it also takes kAutoKernMagicNumber(100000000.000000) With kAutoKernMagicNumber the other Attribute kTextAttrPairKernMethodBoss as of your original posting appears* to get considered.* = I have not loo...

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Adobe Community Professional ,
Nov 03, 2021 Nov 03, 2021

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Hi Olivier,

you should be able to do it very easily using ExtendScript.

That is not the answer you had hoped for, I know, but give that a chance.

 

If you want optical kerning, first apply metrical kerning and as a final step apply optical kerning.

// ExtendScript code
// Given selected text by the user:

app.selection[0].kerningMethod = "$ID/Metrics";
app.selection[0].kerningMethod = "$ID/Optical";

 

Regards,
Uwe Laubender

( ACP )

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Participant ,
Nov 03, 2021 Nov 03, 2021

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Hi Uwe,

Thank you very much for your post.

Can I call ExtendScript from within the SDK ?

Very best regards,

Olivier

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Adobe Community Professional ,
Nov 03, 2021 Nov 03, 2021

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Well, yes.

But don't ask me how…

 

Regards,
Uwe Laubender

( ACP )

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Guide ,
Nov 03, 2021 Nov 03, 2021

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the ClassID value should be kDefaultPairKerningBoss for Automatic

 

The numeric value is stored in a kTextAttrPairKernBoss / IID_ITEXTATTRREALNUMBER.

A display value of 280 is a number of 0.280 ...

 

Optical uses kKFPairKerningBoss as ClassID and a number of kAutoKernMagicNumber

 

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Participant ,
Nov 03, 2021 Nov 03, 2021

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Hi Dirk,

Thank you very much for your post.

By "automatic" do you mean "metric" ?

And in that case is the value of IID_ITEXTATTRREALNUMBER irrelevant ?

Very best regards,

Olivier

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Participant ,
Nov 03, 2021 Nov 03, 2021

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Hello again,

I am almost there.

I am able to specify a specific kerning with:

PMReal UnitsBase1000 = atof(p) / 1000.0;
InterfacePtr<IAttrReport> attrKernValue(SnpTextAttrHelper::CreateTextAttribute<ITextAttrRealNumber, PMReal>(kTextAttrPairKernBoss, UnitsBase1000));
charAttributeBossList->ApplyAttribute(attrKernValue);

I am also able to apply Metric kerning with:

InterfacePtr<IAttrReport> attrMetric(SnpTextAttrHelper::CreateTextAttribute<ITextAttrRealNumber, PMReal>(kTextAttrPairKernBoss, kAutoKernMagicNumber));
charAttributeBossList->ApplyAttribute(attrMetric);

But CreateTextAttribute() returns a null pointer when I try to set the Optical kerning as below:

InterfacePtr<IAttrReport> attrOptical(SnpTextAttrHelper::CreateTextAttribute<ITextAttrRealNumber, PMReal>(kKFPairKerningBoss, kAutoKernMagicNumber));
charAttributeBossList->ApplyAttribute(attrOptical);

I assume that I am just using one wrong parameter for the ClassID, but I cannot figure out which one to use.

Very best regards,

Olivier

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Guide ,
Nov 04, 2021 Nov 04, 2021

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Sorry, too much editing too late in the evening. "Metric".

 

You're dealing with two attributes, kTextAttrPairKernBoss and kTextAttrPairKernMethodBoss

 

Attribute kTextAttrPairKernBoss stores the numeric value in its IID_ITEXTATTRREALNUMBER; limits are -2.000000..10.000000 for regular values, otherwise it also takes kAutoKernMagicNumber(100000000.000000)

 

With kAutoKernMagicNumber the other Attribute kTextAttrPairKernMethodBoss as of your original posting appears* to get considered.

* = I have not looked at the docs, just digging thru some debug output while I flip the setting.

 

Attribute kTextAttrPairKernMethodBoss stores a ClassID value in its IID_ITEXTATTRCLASSID, the values for "kernmethod" are
- kDefaultPairKerningBoss // Metrics
- kKFPairKerningBoss // Optical

These "kernmethod" values are boss classes for a service provider, when you use them as class parameter in CreateTextAttribute you get your NULL.

 

Actually having a look at kPairKerningService there are more values:

kKFPairKerningBoss(0x13803)
kRomanOnlyPairKerningBoss(0x3E65)
kDefaultPairKerningBoss(0x3E64)
kPairKerningOffBoss(0x221)

 

I don't know how to reach the others via the UI, might be leftover from 20 years ago or CJK specific. So if you cover CJK, happy testing.

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Participant ,
Nov 04, 2021 Nov 04, 2021

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You're dealing with two attributes, kTextAttrPairKernBoss and kTextAttrPairKernMethodBoss

 

This was my problem; I wasn't setting both systematically.

It now works like a charm.

Thank you very much for all your help.

Olivier

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