hello deep:
in the biplane.svg,
1. the <style> in <defs>, but Upp is not process <style> in <defs>.(add it)
2. the <style> .cls-1 is not a valid Id, p.ReadId() can't handle it.(use p.ReadIdh() replace it)
3. the svg path, upp can't process cxy,xy,...(add while(p.Char(',')); in PainterPath.cpp)
4. the svg path, (c,s) or (q, t) they are usually used in combination.
when the front of s is not c, the first control point is the last current point, but now upp not handle it.(add a branch to handle the previous command).
I modified the two files.(SvgParser.cpp, PainterPath.cpp) You can replace it, and will see the correct display. I will submit the code later.