Issue 1407 in lilypond: Glyphs with an extra Y-offset are not positioned correctly

[lilypond]

Status: Started
Owner: pnorcks
Labels: Type-Defect Priority-High

New issue 1407 by pnorcks: Glyphs with an extra Y-offset are not positioned  
correctly
http://code.google.com/p/lilypond/issues/detail?id=1407

This is taken from a report by Didi, under the heading "Khmer Unicode does  
not get rendered correctly #3":

http://lists.gnu.org/archive/html/bug-lilypond/2010-05/msg00016.html

The problem is that Pango and LilyPond do not agree on a Y-axis orientation  
for glyph offsets.  That is, Pango provides the glyph-offset value, and  
LilyPond shifts the glyph in the wrong direction.

For example, one of the wrongly-positioned glyphs is this one

(0.0 -0.309423720472441 1.36359832677165 "uni17bb")

This specifies that glyph "uni17bb" has a width of 0, extra X offset of  
-0.31, and extra Y offset of 1.36.

Since the backends expect to see a Y-axis with positive values tending to  
the north, LilyPond offsets the glyph 1.36 units *up*.  The correct offset  
is 1.36 units *down*.