[Bug 829143] [ta_IN] Fix Rendering of Letter RA,RI,RII per GoTN standards

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=829143

--- Comment #12 from Shriramana Sharma <samjnaa at gmail.com> ---
Created attachment 591974
  --> https://bugzilla.redhat.com/attachment.cgi?id=591974&action=edit
ZIP of ODT containing relevant text, PDFs showing current rendering

(In reply to comment #11)
> Updated http://pravins.fedorapeople.org/Lohit-Tamil.ttf this should work on
> Windows as well.

Now it is working somewhat but not totally. See below.

> We have removed Virama ligatures with Consonants since we do not required
> those. With positioning we have complete freedom to place VIRAMA wherever we
> want. 

Well the point was that the GPOS implementations on Windows and Linux seem
different, so unlike the precomposed glyphs (which render identical on both
platforms) the GPOS positioning of pulli on the consonants differ between the
platforms.

> Let me know if you find any difference with enhancements i tried my
> best to keep position same.

On Kubuntu, now the positioning is practically identical as of the released
Lohit Tamil 2.5.1 font with precomposed pulli consonants. So that's fine. I
presume other Linux distros will have the same behaviour.

The thing is, there is still difference in Windows and Kubuntu. On Windows the
placing is still awkward for some of the consonants. I have now attached the
rendering of the same ODT as before on Kubuntu 12.04 LO 3.5.3 and Windows XP LO
3.5.4 (I upgraded the Windows LO just now). You can compare them with the
control PDFs generated by 2.5.1 on both platforms. The position of the pulli on
த ந வ ழ ள ற ஷ ஹ is still too much to the right.

Now the GPOS positioning is obviously different on different platforms (even
though it is not supposed to be) and I realize that you may not be able to
perform testing on Win XP yourself. Supporting proper rendering on Win XP
(which even by Microsoft standards is outdated and has many other rendering
problems) may not be high on your priorities. My request is only that in the
interests of helping people use open fonts even on non-open platforms, you go
back to the precomposed glyphs but to cut down on the font size you can use
composite glyphs which I have described before. 

Given that precomposed glyphs as simple glyphs (with copied outlines) are
already there, using precomposed glyphs as composite glyphs (with referenced
outlines) should not be a problem. If you think all is too much of an effort
and expense on time and resources, I will not object if you give up trying to
fix the rendering on Win XP, and will just maintain my own local fork for usage
on Windows. (I already do so anyway.)

> Did not removed ரி since i did not found matching "VOWEL SING I" in font. So
> let it be. But yes, if we can design U+0BBF (SIGN I) which can match with
> some consonants i would like to update it.

No no, the point was not asking you to remove ரி, the point was to ask you to
restore ரீ.

> Yes, we should remove ரீ series as well but i think we can not remove all
> ligature in that series. 

You can neither remove -ி series nor -ீ series. The cursive connection for each
consonant is simply different. The point is to have a complete set of
precomposed cursively connected set of consonants, so you should restore ரீ.

> Let me know which we can remove without affecting
> overall output. I will update it. May be on another bug

I think it is not worth the effort trying to optimize this. Lohit Tamil is one
of the lightest Lohit fonts. We should rather be trying to optimize more
heavier fonts.

> If you are happy with this enhancements i will update Classical fonts as
> well. Off course not for RA, RI and RII shapes :)

As I said, the rendering on Linux seems to be okay but not on Windows. Please
let me know what you decide regarding using composite glyphs which would help
to maintain same appearance and usability on Windows.

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