[XeTeX] Diacritics in color

[Khaled Hosny]

On Wed, Nov 30, 2011 at 11:10:11AM +0100, Keith J. Schultz wrote:
> Hi All, 
> 
> I jump back in. I will cite anybody because what has been said is correct.
> 
> But,
> 
> 	1) trying to compare a browser, XeTex engine and LuaTeX will not help
> 	    as they have different methods of composing their output.
> 	    That is how they compose and position their glyphs.

As far as OpenType processing is concerned they all should give the same
result, else there is a bug somewhere.

> 	2) Most important a composed Unicode glyph is supposed to be just one color!!

No one talked about composed glyphs (certainly not the OP), it was just
a marginal and unrelated issue to the problem being discussed; coloring
combining marks without breaking OpenType mark positioning.

> 	3) Once you start using color a Unicode composed glyph you no longer are positioning
> 	     a single composed glyph, but two or more glyphs.

So? Again, coloring components of composed glyphs is not what is being
discussed here.

> 	3.a) color designed in TeX at.al is designed be applied to a box and not glyphs!! 

I've hard time understanding what this mean or how the difference, if
any, is material. AFAIK, TeX knows nothing about color, it handled just
like any other driver special which TeX makes no effort to interpret not
to mention "applying" it.

> The question remains how to position the composed glyphs and where and how the color attribute
> is added to the output. 
> 
> There are therefore two solutions:
> 	1) The Tex way:
> 		create a macro to compose the glyph and do the positioning and coloring.
> 
> 	2) The developer way:
> 		change the engine so that it firsts generates the composed glyph and then goes back
> 		and then applies color to the different glyphs. 

3) The post-2000s way; use/build an OpenType font with proper combining
mark positioning and apply the colors to individual glyphs à la what
FireFox/LuaTeX and may be many other does.

Regards,
 Khaled