Re: Clustering Rule in Devanagari Pango Engine

[Owen Taylor <otaylor redhat com>]

Chookij Vanatham <chookij vanatham eng sun com> writes:

> Hi Robert,
> 
> The display only can't be used to check for the clustering.
> We need to check it by moving the I-BEAM and see how it moves as the cluster.

If you look at the patch that Havoc posted recently, you'll see that
the current plan is to separate the concept of clusters for movement
from the concept of cursor positions:

Cursor positions are determined by the is_cursor_position flag
in PangoLogAttr.

Clusters affect display only and are there to organize the mapping
between displays and glyphs. The only affect of clustering on the
display of cursors is that if you have multiple cursor positions
within a single cluster, they are done by linearly interpolating
within the bounds of the cluster. The clustering information is
stored in the PangoGlyphString.

I think this separation simplifies things a lot - it means that
we can do things like make a 'fi' ligature a cluster and still
have a cursor position in the middle of it.


In theory, Havoc's patch should do correct cursor positioning for
Devanagari and just about everything else, though the handling of
hitting Backspace probably still needs more work, and testing is
definitely needed.

Regards,
                                        Owen