# OpenGL.GL.APPLE.specular_vector

OpenGL extension APPLE.specular_vector

This module customises the behaviour of the
OpenGL.raw.GL.APPLE.specular_vector to provide a more
Python-friendly API

Overview (from the spec)

An alternative specular lighting model is enabled by passing
the LIGHT_MODEL_SPECULAR_VECTOR token as the <pname> parameter
to LightModel, and TRUE as the <param> parameter. The specular
vector lighting model calculates the specular intensity as the
dot product of the true reflection vector of the light source
and the vector from the vertex to the viewpoint. This yields
results that are visually similar to but often more realistic
than the existing lighting model.

Mathematically, the specular component s.n in the existing
lighting model calculation is replaced with the following
alternative calculation.

Given three vectors, n, l, and p, where n is the unit normal
vector at the vertex, l is the unit vector from the vertex to
the light position, and p is the unit vector from the vertex
to the viewpoint (or the vector {0,0,1} if
LIGHT_MODEL_LOCAL_VIEWER is false), the specular component is
given by

(2 * cross(n, cross(n, l)) + l) . p

All other lighting model and material parameters (shininess,
spotlight, attenuation, local viewer, and direction/positional
sources) operate normally. The specular vector lighting model
affects both rgba and index modes.

The official definition of this extension is available here:
http://www.opengl.org/registry/specs/APPLE/specular_vector.txt

## Functions

## Constants

GL_LIGHT_MODEL_SPECULAR_VECTOR_APPLE (34224)