[HarfBuzz] [Harfbuzz] Issue in Malayalam String Rendering

[Suresh P.]

I doubt this mod will end up in the a regression of positioning prebase matra in front of ligated cillu. I have seen Uniscribe too disregarding the pres rules. Not sure about its present status.

-suresh

On 11 September 2014 14:36:37 GMT+05:30, Uvaraja Pandian <p.uvaraja at gmail.com> wrote:
>Hi  Team,
>
>
>
>We are using the Harfbuzz 0.9.34 version.
>
>
>
>While rendering the Malayalam string using the Harfbuzz and Freetype
>engine, we see some issues.
>
>
>
>*String used: *ക്കേ
>
>*Unicode value:* 0x0d15, 0x0d4d, 0x0d15, 0x0d47, 0x0000
>
>
>
>*Harfbuzz Output:*
>
>
>
>*Proper Output :*
>
>
>
>*Font File used:* Akruti Family, Since this is a licensed font file, we
>are
>not able to share it.
>
>
>
>*Issue in Detail:*
>
>
>
>In the font file,
>
>script mlym {
>
>  # Malayalam
>
>  feature Akhands;
>
>  feature BelowBaseSubstitutions;
>
>  feature *HalfForms*;
>
>  feature PostBaseForms;
>
>  feature PostBaseSubstitutions;
>
>  feature *PreBaseSubstitutions*;
>
>}
>
>
>
>As per the Harfbuzz implementation, below substitution is happening as
>part
>of the HalfForms ,
>
>0x0d15 & 0x0d4d è XYZ character,
>
>
>
>so the output is XYZ, 0x0d15, 0x0d47
>
>
>
>Final re-ordering happens and rearranges as below,
>
>XYZ, 0x0d15, 0x0d47 è XYZ, 0x0d47, 0x0d15
>
>
>
>As per the PreBaseSubstitutions,
>
>XYZ & 0x0d15 is not matched and the output is not proper.
>
>
>
>In-Order to solve this issue, below changes has been done,
>
>
>
>Final Re-ordering,
>
>PSB for the code changes
>
>
>
>As per the PreBaseSubstitutions,
>
>XYZ & 0x0d15 forms the final character.
>
>
>
>*Code Modifications:*
>
>In the file hb-ot-shape-complex-indic.cc, if we modify the lines as
>below
>in the function final_reordering_syllable() it is working,
>
>
>
>  if (start + 1 < end && start < base) /* Otherwise there can't be any
>pre-base matra characters. */
>
>  {
>
>     /* If we lost track of base, alas, position before last thingy. */
>
>          unsigned int new_pos = base == end ? base - 2 : base - 1;
>
>
>
>/* Malayalam / Tamil do not have "half" forms or explicit virama forms.
>
> * The glyphs formed by 'half' are Chillus or ligated explicit viramas.
>
>     * We want to position matra after them.
>
>     */
>
>          if (buffer->props.script != HB_SCRIPT_MALAYALAM &&
>buffer->props.script != HB_SCRIPT_TAMIL)
>
>         {
>
>                       …
>
>          }
>
>
>
>                    if (start < new_pos && info[new_pos].indic_position
>() != POS_PRE_M)
>
>                       {
>
>                              …
>
>                       } else {
>
>                              …
>
>                       }
>
>        }
>
>  }
>
>
>
>Please comment, will it have any side effect.
>
>
>
>Best Regards,
>
>Uvaraja P.
>
>Sindhura P.
>
>
>------------------------------------------------------------------------
>
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