The main files you'll need are Perlin.h and Perlin.cpp. Upon instantiating a Perlin object, you can produce a smoothed Perlin noise value like so:
Perlin p;
p.noise(x,y,z)
Where x,y,z are floating point values representing a position in 3D space.
You'll also find a FractalNoise class which functions similarly. The difference is that fractal (Brownian) noise combines several octaves of Perlin noise together to produce a more interesting or detailed effect. See the header file documentation for details on how the fractal noise can be controlled.
Under the test directory, there is an executable demo program which generates a classical Perlin noise image. You'll need SDL2 installed to compile and run the demo.
You're free to use this code as you please. If you come up with ways of improving the implementation, I'm all ears!
© Chris Little 2012