GLPOINTPARAMETER(3gl)GLPOINTPARAMETER(3gl)NAME
glPointParameterfARB, glPointParameterfvARB - set point parameters
C SPECIFICATION
void glPointParameterfARB( GLenum name,
GLfloat param )
PARAMETERS
pname Specifies the symbolic name of a single-valued point parameter.
pname can be one of the following: GL_POINT_SIZE_MIN_ARB,
GL_POINT_SIZE_MAX_ARB, or GL_POINT_FADE_THRESHOLD_SIZE_ARB.
param Specifies the value of pname.
C SPECIFICATION
void glPointParameterfvARB( GLenum pname,
const GLfloat *params )
PARAMETERS
pname Specifies the symbolic name of a point parameter.
GL_POINT_SIZE_MIN_ARB, GL_POINT_SIZE_MAX_ARB,
GL_POINT_FADE_THRESHOLD_SIZE_ARB, or GL_POINT_DISTANCE_ATTENUA‐
TION_ARB.
params Specifies a pointer to an array where the value or values of
pname are stored.
DESCRIPTION
Point parameters supports additional geometric characteristics of
points. They can be used to render particles or tiny light sources.
Point parameters 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 point size is multiplied with a distance attenuation factor and
clamped as follows:
derived_size = Clamp(size * sqrt(dist_atten(dist)))
where dist_atten is specified as
dist_atten(d) = 1/(a + b * d + c * d^2)
and 'd' is the eye-coordinate distance from the eye, (0,0,0,1) in eye
coordinates, to the vertex.
The derived point size is clamped to a given range, and then clamped to
the implementation-dependent point size range.
If multisampling is supported and enabled, an implementation may
optionally fade the point alpha instead of allowing the size to go
below a given threshold. In this case, the diameter of the rasterized
point is
/ derived_size if derived_size >= threshold diameter = (
\ threshold
and the fade factor is computed as follows
/ 1 if derived_size >= threshold fadefact = (
\ threshold
The distance attenuation coefficients, 'a', 'b', and 'c', the bounds
of the clamp, and the point fade threshold are specified with glPoint‐
Parameter. If pname is GL_POINT_SIZE_MIN_ARB or GL_POINT_SIZE_MAX_ARB,
then param specifies, or params points to the lower and upper bound
respectively on the derived point size. If the lower bound is greater
than upper bound, the resulting point size is undefined. If pname is
GL_POINT_DISTANCE_ATTENUATION_ARB, then params points to the coeffi‐
cients 'a','b', and 'c'. If pname is GL_POINT_FADE_THRESHOLD_SIZE_ARB,
param specifies, or param points to the point fade threshold.
ERRORS
GL_INVALID_ENUM is generated if glPointParameterfARB parameter pname is
not GL_POINT_SIZE_MIN_ARB, GL_POINT_SIZE_MAX_ARB, or
GL_POINT_FADE_THRESHOLD_SIZE_ARB.
GL_INVALID_ENUM is generated if glPointParameterfvARB parameter pname
is not GL_POINT_SIZE_MIN_ARB, GL_POINT_SIZE_MAX_ARB,
GL_POINT_FADE_THRESHOLD_SIZE_ARB, or GL_POINT_DISTANCE_ATTENUATION_ARB.
GL_INVALID_VALUE is generated when values for GL_POINT_SIZE_MIN_ARB,
GL_POINT_SIZE_MAX_ARB, or GL_POINT_FADE_THRESHOLD_SIZE_ARB are -ve.
30 September 02 GLPOINTPARAMETER(3gl)