Re: [ft-devel] Two patches for FT

[Werner LEMBERG]

> Your screenshot shows that there's something fishy with FreeType's
> TT code.  If you call `ftview -r 96 8 tahoma.ttf' (from the current
> CVS, with bytecode interpreter and patented hinting enabled) you can
> see that both the glyphs `6' and `8' have one pixel too much.
> Either there's a bug in the bytecode interpreter, or there is a
> problem with the dropout code in the renderer.

With the current CVS of fontforge (earlier versions won't work
correctly) I've debugged the instructions of the `8' glyph.  It is a
rounding problem, and it seems to be a very subtle one.  The last
DELTAP1 instruction in the hinting code moves point 17 0.375 units up
(at 11 ppem).  This causes a shape change as shown in the attached
images.  As can be seen, the spline almost hits the pixel center which
decides whether the pixel is on or off.  Within Windows, the pixel
center is *below* the curve, so it is off.  Within FreeType, the pixel
center is *above* (or on) the curve, so it is on.  David?


    Werner