[HarfBuzz] [Harfbuzz] Issue in Malayalam String Rendering

[Uvaraja Pandian]

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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