GLPOINTSIZE(3G) UNIX Programmer's Manual GLPOINTSIZE(3G)
NAME
glPointSize - specify the diameter of rasterized points
C SPECIFICATION
void glPointSize( GLfloat size )
PARAMETERS
size Specifies the diameter of rasterized points. The ini-
tial 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 deter-
mined 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
( | xw | + .5, | yw | + .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
( | xw + .5 |, | yw + .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 raster-
izing a nonantialiased point are assigned the same associ-
ated 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 (xw, yw). The
coverage value for each fragment 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 raster-
ized.
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GLPOINTSIZE(3G) UNIX Programmer's Manual GLPOINTSIZE(3G)
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 sup-
ported; 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_SMOOTH_POINT_SIZE_RANGE and
GL_SMOOTH_POINT_SIZE_GRANULARITY. For aliased points, query
the supported ranges and granularity with glGet with argu-
ments GL_ALIASED_POINT_SIZE_RANGE and
GL_ALIASED_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 speci-
fied value.
A non-antialiased point size may be clamped to an
implementation-dependent maximum. Although this maximum can-
not be queried, it must be no less than the maximum value
for antialiased points, rounded to the nearest integer
value.
GL_POINT_SIZE_RANGE and GL_POINT_SIZE_GRANULARITY are depre-
cated in GL versions 1.2 and greater. Their functionality
has been replaced by GL_SMOOTH_POINT_SIZE_RANGE and
GL_SMOOTH_POINT_SIZE_GRANULARITY.
ERRORS
GL_INVALID_VALUE is generated if size is less than or equal
to 0.
GL_INVALID_OPERATION is generated if glPointSize is executed
between the execution of glBegin and the corresponding exe-
cution of glEnd.
ASSOCIATED GETS
glGet with argument GL_POINT_SIZE
glGet with argument GL_ALIASED_POINT_SIZE_RANGE
glGet with argument GL_ALIASED_POINT_SIZE_GRANULARITY
glGet with argument GL_SMOOTH_POINT_SIZE_RANGE
glGet with argument GL_SMOOTH_POINT_SIZE_GRANULARITY
glIsEnabled with argument GL_POINT_SMOOTH
SEE ALSO
glEnable(3G)
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