Discrepancy in "units per em" between font and SVG

[gsteemso]

I tried BirdFont for the first time yesterday and found it rather frustrating in several respects; most are likely due to operator inexperience, but the issue of attempting to set measurements gave me some real difficulties. I started using the program the easy way, by playing with a copy of an existing font; it had 1024 units per em, and contained no fractional measurements to bloat the file. Alas, as it turned out on examination of the output, BirdFont appears to have been thinking in SVG terms internally, at only 100 units per em! This makes it almost impossible to get accurate positioning of anything. I couldn't find any way to alter that setting from within the program; as such, I'm going to try mucking with the value in the saved XML and see if that achieves anything.

[gsteemso]

Nope, turns out doing it that way would require recalculating every single control-point co-ordinate in the entire font. Not an option.

[johanmattssonm]

Thank you. I have not thought about this before. Would allowing adding an UPM field to the SVG export solve the problem? Do I need to make it possible to customize units in the program as well?

[gsteemso]

After some thought, I believe that allowing it to be set to a consistent value within the application would be the most useful to someone doing fine-detail work on a font; and if you then stored the value explicitly in the output file, it could be checked and/or adjusted by hand if someone really needed to.On Apr 8, 2024, at 12:00 PM, Johan Mattsson ***@***.***> wrote: Thank you. I have not thought about this before. Would allowing adding an UPM field to the SVG export solve the problem? Do I need to make it possible to customize units in the program as well? —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you authored the thread.Message ID: ***@***.***>

[johanmattssonm]

Thank you. That is a great suggestion.

[johanmattssonm]

Hi. I am still thinking about a good solution but I am not sure exactly what you need.

Using other coordinate systems for the object tools is probably easy:

Updating LSB, RSB and kerning is probably also pretty straight forward.

Are there more places where it would be beneficial to use a custom UPM? I am thinking of a solution where the units in the .bf file still are 100 UPM but the designer can chose any UPM to be displayed in the GUI.

[johanmattssonm]

Question number two: should the size of imported SVG files also change? My guess is no but I would like to know what you think.

[gsteemso]

Well, my specific concern was in terms of editing a font in such a way as to not require that fractional measurements be stored in the actual output file, the one your OS tries to load. (When the font contains tens of thousands of characters, the bloat that would introduce is horrifying.) From that perspective, you want to be able to position things using the same units-per-em that the font file is using -- which can be specified by the app when creating from scratch, but is already a fixed value when editing an existing font.

From that perspective, I'm unclear on the utility of being able to specify other coördinate scales. I'm about as far as you can get from a professional typographer, so I am very aware that such a use may exist – I'm just saying I don't know of one.

I confess that I haven't done much at all with SVG stuff. I haven't any experience from which to comment on that aspect of it. I'm sorry I can't offer any useful perspective there.