# OpenGL.GL.EXT.point_parameters

OpenGL extension EXT.point_parameters

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

Overview (from the spec)

This extension supports additional geometric characteristics of points. It
can be used to render particles or tiny light sources, commonly referred
as "Light points".

The raster brightness of a point is a function of the point area, point
color, point transparency, and the response of the display's electron gun
and phosphor. The point area and the point transparency are derived from the
point size, currently provided with the <size> parameter of glPointSize.

The primary motivation is to allow the size of a point to be affected by
distance attenuation. When distance attenuation has an effect, the final
point size decreases as the distance of the point from the eye increases.

The secondary motivation is a mean to control the mapping from the point
size to the raster point area and point transparency. This is done in order
to increase the dynamic range of the raster brightness of points. In other
words, the alpha component of a point may be decreased (and its transparency
increased) as its area shrinks below a defined threshold.

This extension defines a derived point size to be closely related to point
brightness. The brightness of a point is given by:

1
dist_atten(d) = -------------------
a + b * d + c * d^2

brightness(Pe) = Brightness * dist_atten(|Pe|)

where 'Pe' is the point in eye coordinates, and 'Brightness' is some initial
value proportional to the square of the size provided with glPointSize. Here
we simplify the raster brightness to be a function of the rasterized point
area and point transparency.

brightness(Pe) brightness(Pe) >= Threshold_Area
area(Pe) =
Threshold_Area Otherwise

factor(Pe) = brightness(Pe)/Threshold_Area

alpha(Pe) = Alpha * factor(Pe)

where 'Alpha' comes with the point color (possibly modified by lighting).

'Threshold_Area' above is in area units. Thus, it is proportional to the
square of the threshold provided by the programmer through this extension.

The new point size derivation method applies to all points, while the
threshold applies to multisample points only.

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

## Functions

## Constants

GL_DISTANCE_ATTENUATION_EXT (33065)

GL_POINT_FADE_THRESHOLD_SIZE_EXT (33064)

GL_POINT_SIZE_MAX_EXT (33063)

GL_POINT_SIZE_MIN_EXT (33062)