Re: [ft] Using SVG Font Glyph Data In FreeType

[Michiel Kamermans]

Hi Tom, Werner, Andy,

> If you're looking for sample code that reads SVG, I don't think that's 
> something FreeType does. The FreeType side is relatively easy, and Werner has 
> shown you sample code for that. The SVG side is not trivial; it requires XML 
> parsing and should probably be done with a library for SVG (but I don't know 
> what library to recommend).

Depending on how he built his SVG, this should essentially be trivial. 
As long as his SVG consists of paths rather than predefined shapes like 
rectangles and circles (which, given glyph outlines, I wouldn't think he 
uses), these elements have the wonderfully names "d" attribute, which 
contains a normal human readable string of path construction 
instructions. For instance:

<path d="M 10 10 L 30 20 Q 20 40 50 50"/>

In this string, "M" signifies "move to .../...", "L" is "line to 
.../...", and "Q" is "quadratic bezier curve over .../... to .../..." 
(there's also "C" for cubic bezier, and there may be a "Z" at the end of 
the string to signify 'close this path by doing a lineto back to the 
original starting point').

These string segments should be almost trivially simple to map to 
FreeType, since the basic instructions are the same for pretty much all 
things related to fonts: move, line, curve (if you're lucky, 2nd and 3rd 
order, if not, it's just 3rd order with a need to model 2nd order curves 
as 3rd order).

If I understand Andy correctly, he'd like to map these primitive outline 
commands to the corresponding FreeType rules (the FT_outline_Functs 
structures) and then hand off the set of rules for FreeType to work its 
magic on. I've had a look at 
http://freetype.sourceforge.net/freetype2/docs/tutorial/example3.cpp but 
it seems incomplete for the purpose of what he wants to do, as it seems 
to demonstrate how to deal with a purely line data shape, rather than 
one consisting of curve data. The shape as used in the example code uses 
only on-curve vectors, rather than structs that allow specification of 
on-curve coordinates, and off-curve bezier control points.

Andy, if I might ask, where did you get your glyph SVG data from in the 
first place? Are you extracting them from fonts, or are these vector 
outlines made in (for instance) Inkscape that you want to pass to 
FreeType for text rendering?

If the first, is there a reason for not simply using the fonts you 
extracted the glyphs from? If the latter, would it not make more sense 
to do your outline definition in something like FontForge instead, and 
build an actual font that FreeType can use? Of course, option number 
three is you're doing dynamic glyph definitions, using them in 
dynamically generated images with text... but in that case it might be 
far more sensible to build the entire graphic as an SVG image instead.

- Mike "Pomax" Kamermans
nihongoresources.com