LettError/MutatorMath

Add rules data to .designspace.

Closed this issue · 5 comments

LettError commented
Add rules data to .designspace.
LettError commented

This is a proposal for some xml to record conditional glyph substitutions in designspace.

  • I'm not sure if this covers all the conditions allowed by OpenType 1.8
  • this is not proposal for feature language.
  • just covers single glyphs, not groups.
  • does not cover GPOS-like things.
<!-- optional: list of substitution rules -->
    <rules>
        <rule name="vertical bars" enabled="true">
            <sub name="cent" byname="cent.alt"/>
            <sub name="dollar" byname="dollar.alt"/>
            <condition tag="wght" minimum="250.000000" maximum="750.000000"/>
            <condition tag="wdth" minimum="100" maximum="120"/>
            <condition tag="opsz" minimum="10" maximum="40"/>
        </rule>
    </rules>

rules

rules element: groups all the rules. Contains one or more rule elements

rule

rule element: a single rule. Contains one or more sub elements, and one or more condition elements. All conditions must evaluate to true for the rule to be

  • name: attribute, optional. String. Descriptive name for this rule.
  • enabled: attribute, optional. Bool. If this rule should be evaluated or not.

sub

sub element: a single glyph to glyph substitution.

  • name attribute, required. Name of the source glyph.
  • byname attribute, required. Name of the replacement glyph.

condition

condition element: a single condition that has to evaluate to true for this rule to be valid.

  • tag element: attribute, required. OpenType axis tag.
  • minimum attribute, required. Number.
  • maximum attribute, required. Number.
readroberts commented

Looks good to me. The one change is that a condition in OpenType sets a range in which the feature is applied, rather than gt or lt a threshold. How about just 'max' and 'min' instead of 'operator' and 'value'.

See "Condition Table" in https://www.microsoft.com/typography/otspec/chapter2.htm.

  • Read
behdad commented

lgtm

LettError commented

I added rule support to designspaceDocument. More here