OpenType Layout Features - substitution and positioning

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OpenType Layout Features - substitution and positioning

The OpenType Layout Feature specification describes eight types of substitution lookups in the glyph substitution table (GSUB) which are all supported by FontCreator:

#

Type

Description

1

Single

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

2

Multiple

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

3

Alternate

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

4

Ligature

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

5

Context

Substitute one or more glyphs in context

6

Chaining Context

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

7

Extension Substitution

See * below

8

Reverse chaining context

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) which are all supported by FontCreator:

#

Type

Description

1

Single adjustment

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

2

Pair adjustment

Mostly used to define kerning pairs

3

Cursive attachment

Used for scripts that require glyphs to attach to the previous glyphs at exit and entry points

4

Mark‑to‑Base attachment

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

5

Mark‑to‑Ligature attachment

Attach a combining mark to a ligature

6

Mark‑to‑Mark attachment

Attach a combining mark to another mark

7

Context Positioning

Position one or more glyphs in context

8

Chained Context Positioning

Position one or more glyphs in chained context

9

Extension Substitution

See * below

* 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