I've tried running a few fonts through TTX and back and have noticed a few puzzling changes:
(1) All the glyph bounding boxes get recalculated, often to 15% to 25% smaller than original.
(2) The numberOfHMetrics value in one font got changed from 141 to 140.
The questions are:
(1) Can shrinking the bounding boxes cause any compatibility problems with old apps that may have been fine-tuned to use the older, sloppier boxes?
(2) Any idea why TTX would compute a different number of Glyphs than in the original TT font file?
Any answers appreciated.
1) *individual* glyph bounding boxes are not likely to cause a problem. However, if the font-wide bounding box were to change in the Y direction, that could be a big issue for existing documents. Numerous applications, including MS Word, base their line spacing on the font's overall bounding box. It would not affect most professional graphics applications, though.
2) No idea.
Well it's chopping the height range considerably here:
By my math for the x range the difference is about 140
while for the y range 962 + 327 = 1299, while 898 + 263 = 1161, again a considerable change
! <xMin value="-126"/>
! <yMin value="-327"/>
! <xMax value="1573"/>
! <yMax value="962"/>
! <xMin value="-62"/>
! <yMin value="-263"/>
! <xMax value="1509"/>
! <yMax value="898"/>
.. Then again the heigh info in the OS_2 table stays the same, so that maybe has precedence? Hmmmm.....
Have you considered asking the TTX man?