[HarfBuzz] Contextual shaping of Malayalam post(pre)/below base forms

Behdad Esfahbod behdad at behdad.org
Wed Jun 26 08:09:46 PDT 2013

On 13-06-18 06:46 PM, Richard Wordingham wrote:
> lookup pref_st2
>     | y1 xx r3 | -- No sequence indices for this context!
>     | xx r3 |

This wouldn't work.  You should match y1 in backtrack sequence, not input
sequence.  Otherwise this is what happens, if you have a sequence y1 xx r3:

  - HB tries applying the lookup at position zero, matches the first rule, stops,

  - It then advances position by one, trying to apply the rule at position
one, now the second rule matches and ligature is formed.

For a rule to stop a later one from applying they should apply to the same
input sequence at the same position, ie, both should have "xx r3" as their
input, and the first one should have more context in terms of backtrack /
lookahead...  It can have a longer input sequence too, but they should start
the same.


>        0 pref_lkp1
> end lookup


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