OpenType Layout Features - Supported types of substitution and positioning

Previous  Next

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

#

Type

Script

Designer

Description

1

Single

Yes

No

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

2

Multiple

Yes

No

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

3

Alternate

Yes

No

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

4

Ligature

Yes

No

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

5

Context

No

No

Substitute one or more glyphs in context

6

Chaining Context

Partially

No

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

7

Extension Substitution

No*

No


8

Reverse chaining context

No

No

Applied in reverse order, replace single glyph in chaining context

The OpenType Layout Feature specification describes nine types of positioning (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

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

3

Cursive attachment

No

No

 

4

Mark to base attachment

Yes

Yes

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

5

Mark to ligature attachment

No

No

Attach a combining mark to a ligature

6

Mark to mark attachment

Yes

Yes

Attach a combining mark to another mark

7

Context Positioning

No

No

Position one or more glyphs in context

8

Chained Context Positioning

Partially

Yes

Position one or more glyphs in chained context

9

Extension Substitution

No*

No*


* 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.