[HarfBuzz] harfbuzz coordinate system

[Behdad Esfahbod]

Hi all,

I'm wondering, should increasing y move upwards, or downwards?  Most graphics
API I've seen (PS-based API being the only exception) has y moving downward.
I find that more intuitive in a text layout library, so we can say: "in-line
glyphs are stacked in the increasing x direction, lines are stacked in the
increasing y direction."

Does everyone agree?

If we agree, I need to change it all around the code since currently y
direction is upward, which is what the OpenType font-space is.

behdad