These are some utilities ported over from the CairoWidget project. Qt's own SVG rendering is notoriously slow and buggy, it can even crash your program. NanoSVG, while also buggy and incomplete, is an easy and reliable alternative. Using vector graphics in your project solves the problem of resolution-independent resources for your buttons and other controls.
If the SVG implementations of NanoSVG or Qt were complete, implementing animated gauges and other rich controls would become easier.
git submodule update --init
qmake
make