OpenGL man pages
glPointSize - specify the diameter of rasterized points
void glPointSize( GLfloat size )
size Specifies the diameter of rasterized points. The default is 1.0.
glPointSize specifies the rasterized diameter of both aliased and
antialiased points. Using a point size other than 1.0 has different
effects, depending on whether point antialiasing is enabled. Point
antialiasing is controlled by calling glEnable and glDisable with argument
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
( floor(x )+.5, floor(y )+.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
( floor(x +.5), floor(y +.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 produces 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 , y ). 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 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 1.0 is guaranteed to be supported; others depend on the
implementation. The range of supported sizes and the size difference
between supported sizes within the range can be queried by calling glGet
with arguments GL_POINT_SIZE_RANGE and GL_POINT_SIZE_GRANULARITY.
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 specified value.
Non-antialiased point size may be clamped to an implementation-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
GL_INVALID_VALUE is generated if size is less than or equal to zero.
GL_INVALID_OPERATION is generated if glPointSize is executed between the
execution of glBegin and the corresponding execution of glEnd.
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
Fri Dec 6 11:18:03 EST 1996
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