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

[Suresh P]

Behdad Esfahbod wrote:
> 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.
>
> b
Thanks for the insightful explanation. I had non-contextual lookups too. 
Removing them solved the issues.
>
>>         0 pref_lkp1
>> end lookup