Contextual Spacing GPOS Features—Redux

On this date last year, I published the Contextual Spacing GPOS Features article, and this briefer article serves as an update.

Two important steps toward implementation were taken during the past year:

  1. I started the process of registering the two GPOS features: 'chws' (“Contextual Half-width Spacing”) and 'vchw' (“Vertical Contextual Half-width Spacing”). There was some discussion on the OpenType and OFF (Open Font Format; aka the ISO/IEC 14496:22 standard that is available free here) mailing lists, and the conclusion was that the originally-proposed feature tags and their friendly names, 'cspc' (“Contextual Spacing”) and 'vcsp' (“Vertical Contextual Spacing”), didn’t convey an important characteristic of the features, specifically that they involve half-width spacing.
  2. Thanks to feedback received from that article, especially that from Koji Ishii (石井宏治), I modified the contextual rules and produced SourceHanSerifCSP-Heavy.otf Version 1.005. The raw features file that uses Unicode-based working glyph names is a helpful resource to understand the scope of these GPOS features.

With regard to the second step, the changes that were made, compared to Version 1.004, were 1) the @ColonExclamQuestion and @ColonExclamQuestionVert glyph classes that include the glyphs for the exclamation and question marks, along with left-justified forms of the colon and semicolon, were removed, as were their contexts; 2) quarter-width metrics adjustments were removed; 3) contexts that include centered punctuation followed by another centered punctuation or a full-width space were removed; and 4) contexts that include a justified period or comma followed by centered punctuation were added.

In closing, the animated image below is identical to the one in the previous article, but has been made using the latest font (none of the changes affected this particular text), and better illustrates the advantages of these GPOS features in environments with limited line-layout capabilities:

As usual, any and all feedback is greatly appreciated!


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