# OpenGL.GL.NV.fog_distance

OpenGL extension NV.fog_distance

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

Overview (from the spec)

Ideally, the fog distance (used to compute the fog factor as
described in Section 3.10) should be computed as the per-fragment
Euclidean distance to the fragment center from the eye. In practice,
implementations "may choose to approximate the eye-coordinate
distance from the eye to each fragment center by abs(ze). Further,
fog factor
f need not be computed at each fragment, but may
be computed at each vertex and interpolated as other data are."

This extension provides the application specific control over how
OpenGL computes the distance used in computing the fog factor.

The extension supports three fog distance modes: "eye plane absolute",
where the fog distance is the absolute planar distance from the eye
plane (i.e., OpenGL's standard implementation allowance as cited above);
"eye plane", where the fog distance is the signed planar distance
from the eye plane; and "eye radial", where the fog distance is
computed as a Euclidean distance. In the case of the eye radial
fog distance mode, the distance may be computed per-vertex and then
interpolated per-fragment.

The intent of this extension is to provide applications with better
control over the tradeoff between performance and fog quality.
The "eye planar" modes (signed or absolute) are straightforward
to implement with good performance, but scenes are consistently
under-fogged at the edges of the field of view. The "eye radial"
mode can provide for more accurate fog at the edges of the field of
view, but this assumes that either the eye radial fog distance is
computed per-fragment, or if the fog distance is computed per-vertex
and then interpolated per-fragment, then the scene must be
sufficiently tessellated.

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

## Functions

## Constants

GL_EYE_PLANE (9474)

GL_EYE_PLANE_ABSOLUTE_NV (34140)

GL_EYE_RADIAL_NV (34139)

GL_FOG_DISTANCE_MODE_NV (34138)