bugFree UCS Outline Fonts - Bugs: bug #50482, Half form of Bengali ta is khanda...

 
 

bug #50482: Half form of Bengali ta is khanda ta in FreeSerif

Submitter:  David Corbett <dscorbett>
Submitted:  Tue 07 Mar 2017 04:32:48 PM UTC
   
 
Category:  individual character(s) Severity:  3 - Normal
Item Group:  character substitution issue Status:  Fix posted
Privacy:  Public Assigned to:  Stevan_White
Open/Closed:  Open Release:  * development
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Sun 20 Aug 2017 09:49:00 AM UTC, comment #5: 

The latest commit should resolve this. 
See revised test file attached.
Thanks, David!

(file #41585)

Steve White <Stevan_White>
Group administrator
Sun 23 Apr 2017 02:09:04 PM UTC, comment #4: 


> What you're saying is, ta has no half form whatsoever.

Right. As http://www.unicode.org/L2/L2004/04262-bengali-pr-30.pdf says, “A half-form reduced-size ta glyph may have existed in some font implementations for creation of certain connected-conjunct forms, but a non-connected reduced-size ta is not known to be in attested usage.”

David Corbett <dscorbett>
Sun 23 Apr 2017 11:56:37 AM UTC, comment #3: 

Hi David,

I am struggling to harmonize your statement with the standards statement

In Bengali, a dead consonant ta makes use of a special form, U+09CE bengali letter khanda ta. This form is used in all contexts except where it is immediately followed by one of the consonants: ta, tha, na, ba, ma, ya, or ra.

Your example is a combination of ta with ga. So that statement applied in this situation, would mean the ta "dead consonant" is used.  I think I had been taking a "dead consonant" in Bengali to be the half form -- but of course that is a further tranformation of a dead consonant.  What you're saying is, ta has no half form whatsoever.

OK  I think I got it, and I already have a solution.  What I haven't yet found is an image illustrating this behavior.  (In fact, if you're right -- this would have been a very nice case to list in table 12-13.)

Steve White <Stevan_White>
Group administrator
Fri 21 Apr 2017 05:55:20 PM UTC, comment #2: 

I will try to explain how ta works, then explain what changes the font needs.

U+09A4 BENGALI LETTER TA behaves like any other Indic consonant letter. It can participate in stacked conjuncts; the exact set depends on the font, but Unicode gives tta as an example. If a font does not have a glyph for a particular cluster, e.g. tka, the ta takes an explicit hasant. It never looks like U+09CE BENGALI LETTER KHANDA TA (except in the compatibility sequence U+09A4 U+09CD U+200D).

U+09CE BENGALI LETTER KHANDA TA is, as far as Unicode is concerned, a completely different letter. It doesn’t take a hasant or a vowel mark.

The sentence “This form is used in all contexts except where it is immediately followed by one of the consonants: ta, tha, na, ba, ma, ya, or ra.” means that the dead consonant t is written as khanda ta except when the dead consonant t is followed by one of the listed consonants. For example, tpa would use the khanda ta glyph, but tba would not. This paragraph of the standard is explaining Bengali orthographic rules; it does not mean that U+09A4 should use the khanda ta form before consonants not in the list.

In your test page, the only misrenderings are ⟨ত্গ⟩ and ⟨ত্ক⟩, wherein the sequence U+09A4 U+09CD uses the khanda ta glyph. This is wrong. The sequence U+09A4 U+09CD should use the ta glyph with the hasant glyph below. The new glyph called “bn_ta.half” is erroneous and should be deleted, and all the lookups that use bn_ta.half should use ta_bng hasanta_bng instead.

David Corbett <dscorbett>
Fri 21 Apr 2017 09:24:36 AM UTC, comment #1: 

I'm not sure I understand your remarks, and I'm not sure I understand the standard, and I'm not sure you understand the standard.  This isn't surprising, because the explanation in the standard starts off with inanimate objects "making use" of other inanimate objects.  The writing could stand some improvement.

My take on it is this.  Unlike other consonants, ta has two different "dead" forms.  They look the same but behave differently in combinations.  The usual "dead" form for ta is produced in the usual way with hasanta.  The other, khanda ta, can be produced in either of the two ways you describe.

In contrast to the half-form ta, khanda ta does not form conjunct ligatures.  So with it, it is possible to produce a "dead" ta glyph without hasanta, followed by a consonant, as in the figure in the standard.

I don't understand the remarks about vowels or the reph.  Maybe the key is the the second sentence "This form is used in all contexts except ...".  Unfortunately that sentence contains an "it" whose reference is unclear to me.

The commit I just made satisfies what I can make of the description in the standard, except that the "la" is still being combined with khanda ta. (Given the level of precision of the rest of the explanation, I have to wonder if "la" was an omission.)

Attached find a test page.


(file #40463)

Steve White <Stevan_White>
Group administrator
Tue 07 Mar 2017 04:32:48 PM UTC, original submission:  

In FreeSerif, the half form of U+09A4 BENGALI LETTER TA uses the glyph of U+09CE BENGALI LETTER KHANDA TA. That means that ⟨ত্গ⟩ (tgô) looks like ⟨ৎগ⟩, but it should look like ⟨ত্‌গ⟩; that is, it should have a visible virama. The khanda ta glyph should only appear in two cases:

  • U+09CE BENGALI LETTER KHANDA TA (preferred)
  • U+09A4 BENGALI LETTER TA, U+09CD BENGALI SIGN VIRAMA, U+200D ZERO WIDTH JOINER (for compatibility with Unicode 4.0.1 and earlier)


See The Unicode Standard version 9.0, ch. 12, section “Khanda Ta”.

David Corbett <dscorbett>

 

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Attached Files
file #41585:  bengali-khanda-ta.html added by Stevan_White (4KiB - text/html - revised to switch fonts)

 

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    Date Changed by Updated Field Previous Value => Replaced by
    2017-08-20 Stevan_White Attached File- Added bengali-khanda-ta.html, #41585
        StatusProceeding Fix posted
    2017-04-21 Stevan_White Attached File- Added bengali-khanda-ta.html, #40463
        StatusNone Proceeding
        Assigned toNone Stevan_White

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