Using svg.draw(pen) and parse_path() from svgLib threw exception
ValueError: could not convert string to float: 'a'
on a SVG <path> string generated by Inkscape. Altering the path
string might object to other string bits like 'Z' or 'v', or
give even stranger exceptions.
Finally tracked it down to the path containing particular valid
numbers like "-4e-5" or "1e-4". Changing these to "-4.0e-5" or
"1.0e-4" would stop the exceptions. The parse_path() was not
accepting valid SVG real numbers.
The specification for real number formats is a bit of a mess in
CSS land right now, but the reassuringly concrete spec is:
https://www.w3.org/TR/css-syntax-3/#number-token-diagram
which allows a real number having an exponent but without having
a fractional part, such as the number "1e3".
This change updates an RE to make fractional parts optional,
and adds a test for this valid SVG number format.
SVG documentation has an explicit requirement that _consumers_
of path arc commands accept and *correct* certain bad values.
This includes using the absolute value of the arc command's rx
and ry radius parameters.
See "9.5.1. Out-of-range elliptical arc parameters"
https://www.w3.org/TR/SVG/paths.html#PathDataEllipticalArcCommands
Lib\fontTools\svgLib\path\parser.py is missing any guard against
negative values for rx and ry parameter. Adding an abs() to each
value read will implement the SVG specification.
A problem was seen here while most programs and browsers handle
bad arc commands just fine. A bug report has been registered with
Inkscape (!) to protect any other non-SVG compliant programs.
See https://gitlab.com/inkscape/inbox/-/issues/6857 for more details.
* Replaced all from ...py23 import * with explicit name imports, or removed completely when possible.
* Replaced tounicode() with tostr()
* Changed all BytesIO ans StringIO imports to from io import ..., replaced all UnicodeIO with StringIO.
* Replaced all unichr() with chr()
* Misc minor tweaks and fixes
Some SVG authoring tool write arc commands without any space or comma around the boolean 'large-arc' and 'sweep' flags, leading our svg path parser to choke.
This makes the path parser smarter by special-casing arc command parsing so that it only consumes one character ('0' or '1') for these special boolean flags.
Implement the arc to curve points calculation using the original
svg.path library and use the curve points for the pen.
The Arc class and methods to parameterize and get curve points are
copied.
This makes the svg to glif conversion possible for any SVGs.
