The FAQ is unclear about potential rounding of coordinates in PostScript

[elmimmo]

The FAQ, in the question Is it safe to use non-integral coordinates? states that:

PostScript (type1, PostScript OpenType, type2, etc.) fonts can express non-integral coordinates in the font format–but it takes a lot more space in the font file. Type1 fonts tend to take more space to express this than type2 (opentype) fonts. By default FontForge will round to int on these as well, BUT you can change that in the Generate Options dialog.

but then afterwards, in the question How does FontForge convert a quadratic spline into a cubic (when reading truetype)? it notes that:

[When converting from quadratic to cubic splines] probably the control points will no longer be at integral coordinates and there will be some loss of precision when they are saved in a cubic format.

I guess the FAQ means that the above will happen "when they are saved in a cubic format with default settings in the Generate Options dialog" which, according to the answer to the other question, have “round to int” irrespective of the output format.

I take it then that setting “round to int” to off would indeed allow generating PostScript outlines from a Truetype input without any precision loss whatsoever, right?

[ghost]

Even with round to int turned off, I think there is some limit to the amount of precision stored in the font file (perhaps six or eight digits after the decimal point) and that's the main way in which some precision may be lost.

Beyond file format issues, there is a finite limit to how precise FontForge's internal representation of numbers can be at all (typically double-precision IEEE floating point, equivalent to about 16 decimal digits) and you can only maintain at most that much precision through any cubic/quadratic conversion.

It's unlikely that these issues would really be a problem for anybody, but "I loaded and saved a file and the result wasn't bit-for-bit identical" is a common complaint and this FAQ answer is trying to answer that kind of concern.

[elmimmo]

Thanks for clearing that up.

[davelab6]

I'll keep this open until the FAQ is updated :)