A small and simple geometry library for 3D graphics.
This won't be suitable for use in your projects! I recommend GLM instead; it has many more useful features (and is inevitably more rigorously tested).
The advantage of geom.h, though, is that it is not heavily templated like GLM, and so provides easier reference.
geom.h is just the one header. All you need to do is:
#include "geom.h" for C files that need it
#define GEOM_CPP
#include "geom.h"
for files that use the C++ API
#define GEOM_IMPL
#include "geom.h"
#undef GEOM_IMPL
from ONE file exactly (again, with the extra #define GEOM_CPP if you use the C++ API)
To compile C, you will need the flags -std=c99 and -lm.
All matrices are in column-major order, i.e., geom::mat3(a, b, c, d, ... ) will store those values top-to-bottom, then left-to-right, like this:
a d ..
b . .
c . .
This is the same convention OpenGL uses for its matrices.
Quaternions are stored <x, y, z, w>, i.e., the three imaginary parts first, the real part last. 'axisAngle's, geom_aa or geom::axisAngle, are just an axis and an angle, stored consecutively in that order.