[ft-devel] Alignment of top of capital letters to pixel grid, autohinter often 1 pixel off compared to unhinted outline

[Nikolaus Waxweiler]

While testing Alexei's scaling trick, I rediscovered an old source of 
irritation (apart from the barely visible dot on the "i").

1. Download https://www.google.com/fonts#UsePlace:use/Collection:Open+Sans
2. Load OpenSans-Regular.ttf in ftview, look at sizes 10, 13, 15, 19
3. Press A and B and compare where the bytecode and the autohinter align 
the top of capital letters, also press h to compare with the unhinted 
outline.

I've noticed similar behavior by the autohinter in other fonts. Snapping 
1 pixel too low like at the above sizes makes glyphs look like someone 
stepped on them, 1 pixel too high is a bit less of an issue I think, 
depending on the size. Bytecode and the CFF hinter do that, too, 
sometimes, but e.g. the CFF hinter in general and the bytecode in this 
example give me a better overall consistency impression..

What is the cause and is there anything to be done about it?