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