The online source documentation is located at http://www.freecadweb.org/api/
The FreeCAD source code is commented to allow automatic html documentation generation with Doxygen. This is the case for both the C++ and Python parts of the FreeCAD source code.
For those wanting to follow closely the latest development versions of FreeCAD, and who try to have a look at the C++ or Python parts, the first insight in the sources can give the feeling you're looking at an hedgehog: you can't discriminate head from tail and don't really know how to catch it!
In complement to this Wiki, the Source Documentation can hopefully alleviate this feeling, providing an entry point, and allowing for easy browsing through the dozens of files and directories.
If you have Doxygen installed, it's very easy to build the doc. Go to your FreeCAD build directory, configure your sources with CMake, issue
and consult the resulting html files starting from Doc/SourceDocu/html/index.html .
The DevDoc make target above will, if graphviz is installed on your system, generate a 2Gb+ volume of data. An alternative, smaller version (~500Mb), that is the version used on http://www.freecadweb.org/api/ can also be generated by issuing instead:
By nature, source doc is, and will ever be, work in progress. Don't hesitate to rebuild as often as needed. If you fall upon blatant inadequacies, feel free to post on the forum (note: It is really fully checked with cMake build process only).
As an alternative, the doc is generated from time to time and accessible on sourceforge here.
On unix systems, it is possible to link Coin3D source documentation with FreeCAD's. It allows easier navigation and complete inheritance diagrams for Coin derived classes.
Example of a complete doxygen page: (from another project)