[HarfBuzz] more complete feature/mask control

[Jonathan Kew]

On 28 May 2010, at 22:44, Behdad Esfahbod wrote:

> Thanks Jonathan,
> 
> It gives me a starting point.  I'll commit and start working on it.
> 
> BTW, I realized that in or_masks(), we can't really binary search because:
> 
>  1) While hb_buffer_add_utf*() set ->cluster to be src index, the user is
> free to modify those to be some other value they find useful for future
> retrieval (or use hb_buffer_add() instead).

Hmm... well, personally I think you should rename the cluster field to be src_index and define that this IS what it means. The user can't change it to be anything else, or the entire feature start/end API is broken anyway.

> 
>  2) If ensure_direction() reversed the buffer, ->cluster is not increasing
> anymore.

True, we'd have to have two versions of the search, to handle forward or reversed buffers.....

> 
>  3) Since we also reverse_clusters() in ensure_direction(), the ->cluster
> array may not even be monotonic.

....but this complicates things further, yes.

> 
> We probably can do something like walking over it once and see if it is
> monotone and save the result and bsearch if it is.

Perhaps, but given the factors you've mentioned, I suggest using the "dumb" implementation for now, and we can consider optimizing later.

The most common case will in any case be start=0, end=-1, which is optimized via the global_mask so that only one iteration over the buffer is needed for any number of features.

JK