OpenType Layout Features - Supported types of substitution and positioning

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The OpenType Layout Feature specification describes eight types of substitution lookups in the glyph substitution table (GSUB). The following table shows those currently supported by FontCreator:

#

Type

Script

Designer

Description

1

Single

Yes

Yes

Substitute a single glyph by another single glyph (a -> b)

2

Multiple

Yes

Yes

Substitute a single glyph by other multiple glyphs (a -> xyz)

3

Alternate

Yes

Yes

Substitute a single glyph by one of multiple alternates (a -> x or y or z)

4

Ligature

Yes

Yes

Substitute multiple glyphs by a single ligature (f f i -> ffi)

5

Context

Yes

Yes

Substitute one or more glyphs in context

6

Chaining Context

Yes

Yes

Substitute context specific glyphs (3rd -> 3rd)

7

Extension Substitution

Auto*

Auto*


8

Reverse chaining context

Yes

Yes

Applied in reverse order, replace single glyph in chaining context

The OpenType Layout Feature specification describes nine types of positioning lookups in the glyph positioning table (GPOS). The following table shows those currently supported by FontCreator:

#

Type

Script

Designer

Description

1

Single adjustment

Yes

Yes

Change the position of a single glyph (sub/superscript)

2

Pair adjustment

Yes

Yes

Mostly used to define kerning pairs

3

Cursive attachment

Yes

Yes

 

4

Mark to base attachment

Yes

Yes

Attach a combining mark such as a diacritic to a base glyph

5

Mark to ligature attachment

Yes

Yes

Attach a combining mark to a ligature

6

Mark to mark attachment

Yes

Yes

Attach a combining mark to another mark

7

Context Positioning

Yes

Yes

Position one or more glyphs in context

8

Chained Context Positioning

Yes

Yes

Position one or more glyphs in chained context

9

Extension Substitution

Auto*

Auto*


* Extension substitution is a special kind of lookup that is only used for fonts with a lot of features. FontCreator will automatically include such lookup if needed.

 

In addition FontCreator also supports all feature parameters currently defined.

 

So basically FontCreator supports all OpenType Layout Features. For an up-to-date list of things currently not fully supported, please visit our forums at http://forum.high-logic.com/viewtopic.php?f=4&t=5098