Using OpenType Feature Tables in Arbortext Layout Developer
To use OpenType Feature Tables in Layout Developer, there are two main parts to be aware of. Firstly, one must turn on OpenType word shaping and secondly one must activate the desired Feature Tables. The properties to do this are provided as part of the fStyle object within the Formatting Object Model. Using the fStyle object allows OpenType to be selectively turned off/on on an inline basis, rather than globally. As fStyle is inheritable as part of Layout Developer’s block model (using fBlock.defaultStyle), a document or chapter preference can also be set.
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Layout Developer can only use OpenType features which are provided as part of the font files installed on the machine it is being used. Layout Developer cannot create Feature Tables which are not there! For this reason, the fTypeface object has been updated to provide information on which OpenType features are available to be used. More on this later.
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To turn on OpenType word shaping, use something like this:
formatting.currentStyle.useOpenType = true;
This tells Layout Developer to start using OpenType word shaping which will then apply the default set of Feature Tables. You could also use:
var b = new fBlock();
var s = b.defaultStyle;
s.useOpenType = true;
formatting.blockStart(b);
This will activate the OpenType word shaping within Layout Developer which will use any default Feature Tables active for that font but as it is applied to a block, descendant blocks and paragraphs will inherit this setting.
If we want to simply change the set of active Feature Tables, they can be turned on or off using the following command:
formatting.currentStyle.openTypeFeatures = fTypeface.OT_FEATURE_SUBSCRIPT;
If more than one Feature Table is to be turned on at a time, the features can be chained together like this:
formatting.currentStyle.openTypeFeatures = fTypeface.OT_FEATURE_SUBSCRIPT + fTypeface.OT_FEATURE_SUBSCRIPT + fTypeface.OT_FEATURE_SWASH;
When setting the Feature Tables using fStyle.openTypeFeatures, the list of features provided is the list of features which will be applied. This property sets the list, it cannot be used to add or remove feature tables from a maintained list.
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The “frac” Feature Table in some fonts allows fractions to be built from numbers. In order for the word shaping engine to recognise the ‘/’ correctly, it is necessary to remove that character as a word break character using <?twbch -”/”?> or fStyle.hyphenationBreakCharacters = “-”.
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