[Following on from recent discussion on the Unicode list regarding
automating the use of colour as an aspect of line layout, particularly for
I think Marco is still on holiday but, just before he left, he and I
devised a method to enable bi-chromatic Ethiopic punctuation by utilising a
function similar to the MS Word 'Different colour for diacritics' function
in combination with a new Chromatic Display <chro> OpenType Layout feature.
Ideally, an application would provide a single UI function 'Ethiopic
coloured punctuation' which would apply the <chro> feature and then apply
the colouring. The <chro> layout feature is a little unusual for having
both a GSUB and a GPOS component.
The <chro> feature first applies a one-to-many substitution to split the
representation of the punctuation character into two glyphs. The first
glyph is base punctuation glyph (the black bit) and the second glyph is the
enhancement (the red bit). The trick is that the second glyph is classified
as a 'mark' in the GDEF table and is positioned relative to the base
punctuation glyph using the <mark> GPOS feature.
The application then applies colour to any 'mark' glyphs in the run, using
the GDEF table information as a guide (this is how the coloured Arabic
diacritics in Word already work).
Tiro Typeworks www.tiro.com
Vancouver, BC email@example.com
Language must belong to the Other -- to my linguistic community
as a whole -- before it can belong to me, so that the self comes to its
unique articulation in a medium which is always at some level
indifferent to it. - Terry Eagleton
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