Applying Metric or Optical Kerning

[Olivier Beltrami]

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

[Laubender]

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 )

[Olivier Beltrami]

Hi Uwe,

Thank you very much for your post.

Can I call ExtendScript from within the SDK ?

Very best regards,

Olivier

[Laubender]

Well, yes.

But don't ask me how…

Regards,
Uwe Laubender

( ACP )

[Dirk Becker]

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

[Olivier Beltrami]

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

[Olivier Beltrami]

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

[Dirk Becker · Accepted solution]

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.

[Olivier Beltrami]

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