Contents

• Dependencies
• Overview
• New Procedures and Functions
• New Tokens
• Errors
• New State
• New Implementation Dependent State

Dependencies

OpenGL 1.0 is required.

GL_ARB_multisample affects the definition of this extension.

The extension is written against the OpenGL 1.2.1 Specification.

Overview

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

New Procedures and Functions

``` void PointParameterfARB(enum pname, float param);

void PointParameterfvARB(enum pname, float *params); ```

New Tokens

Accepted by the

<pname>

parameter of PointParameterfARB, and the

<pname>

of Get:

|POINT_SIZE_MIN_ARB| |:--------------------| |POINT_SIZE_MAX_ARB| |POINT_FADE_THRESHOLD_SIZE_ARB|

Accepted by the

<pname>

parameter of PointParameterfvARB, and the

<pname>

of Get:

|POINT_SIZE_MIN_ARB | 0x8126| |:---------------------------------|:------| |POINT_SIZE_MAX_ARB | 0x8127| |POINT_FADE_THRESHOLD_SIZE_ARB | 0x8128| |POINT_DISTANCE_ATTENUATION_ARB | 0x8129|

Errors

INVALID_ENUM is generated if PointParameterfARB parameter

<pname>

is not POINT_SIZE_MIN_ARB, POINT_SIZE_MAX_ARB, or POINT_FADE_THRESHOLD_SIZE_ARB.

INVALID_ENUM is generated if PointParameterfvARB parameter

<pname>

is not POINT_SIZE_MIN_ARB, POINT_SIZE_MAX_ARB, POINT_FADE_THRESHOLD_SIZE_ARB, or POINT_DISTANCE_ATTENUATION_ARB

INVALID_VALUE is generated when values are out of range according to:

|

<pname>

| valid range | |:-----------------|:----------------| |POINT_SIZE_MIN_ARB | >= 0 | |POINT_SIZE_MAX_ARB | >= 0 | |POINT_FADE_THRESHOLD_SIZE_ARB | >= 0 |

New State

New Implementation Dependent State

None