GLPOINTSIZE() MachTen Programmer’s Manual GLPOINTSIZE()

NAME
glPointSize - specify the diameter of rasterized points

C SPECIFICATION
void glPointSize( GLfloat size )

delim $$

PARAMETERS
size Specifies the diameter of rasterized points. The
initial value is 1.

DESCRIPTION
glPointSize specifies the rasterized diameter of both
aliased and antialiased points. Using a point size other
than 1 has different effects, depending on whether point
antialiasing is enabled. To enable and disable point
antialiasing, call glEnable and glDisable with argument
GL_POINT_SMOOTH. Point antialiasing is initially disabled.

If point antialiasing is disabled, the actual size is
determined by rounding the supplied size to the nearest
integer. (If the rounding results in the value 0, it is
as if the point size were 1.) If the rounded size is odd,
then the center point ($ x $, $ y $) of the pixel fragment
that represents the point is computed as

( $ | ~ x sub w ~ | ~+~ .5 $, $ | ~ y sub w ~ | ~+~ .5 $)

where $w$ subscripts indicate window coordinates. All
pixels that lie within the square grid of the rounded size
centered at ($ x $, $ y $) make up the fragment. If the
size is even, the center point is

( $ | ~ x sub w ~+~ .5 ~ |$, $ | ~ y sub w ~+~ .5 ~ | $)

and the rasterized fragment’s centers are the half-integer
window coordinates within the square of the rounded size
centered at ($ x $, $ y $). All pixel fragments produced
in rasterizing a nonantialiased point are assigned the
same associated data, that of the vertex corresponding to
the point.

If antialiasing is enabled, then point rasterization pro-
duces a fragment for each pixel square that intersects the
region lying within the circle having diameter equal to
the current point size and centered at the point’s ($ x
sub w $, $ y sub w $). The coverage value for each frag-
ment is the window coordinate area of the intersection of
the circular region with the corresponding pixel square.
This value is saved and used in the final rasterization
step. The data associated with each fragment is the data
associated with the point being rasterized.

Not all sizes are supported when point antialiasing is
enabled. If an unsupported size is requested, the nearest
supported size is used. Only size 1 is guaranteed to be
supported; others depend on the implementation. To query
the range of supported sizes and the size difference
between supported sizes within the range, call glGet with
arguments GL_POINT_SIZE_RANGE and
GL_POINT_SIZE_GRANULARITY.

NOTES
The point size specified by glPointSize is always returned
when GL_POINT_SIZE is queried. Clamping and rounding for
aliased and antialiased points have no effect on the spec-
ified value.

A non-antialiased point size may be clamped to an imple-
mentation-dependent maximum. Although this maximum cannot
be queried, it must be no less than the maximum value for
antialiased points, rounded to the nearest integer value.

ERRORS
GL_INVALID_VALUE is generated if size is less than or
equal to 0.

GL_INVALID_OPERATION is generated if glPointSize is exe-
cuted between the execution of glBegin and the correspond-
ing execution of glEnd.

ASSOCIATED GETS
glGet with argument GL_POINT_SIZE
glGet with argument GL_POINT_SIZE_RANGE
glGet with argument GL_POINT_SIZE_GRANULARITY
glIsEnabled with argument GL_POINT_SMOOTH

SEE ALSO
glEnable

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