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 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.

The specified point size is multiplied with a distance attenuation factor and clamped to the specified point size range, and further clamped to the implementation-dependent point size range to produce the derived point size using

pointSize = clamp ⁢ size × 1 a + b × d + c × d 2

where d is the eye-coordinate distance from the eye to the vertex, and a, b, and c are the distance attenuation coefficients (see glPointParameter()).

If multisampling is disabled, the computed point size is used as the point's width.

If multisampling is enabled, the point may be faded by modifying the point alpha value (see glSampleCoverage()) instead of allowing the point width to go below a given threshold (see glPointParameter()). In this case, the width is further modified in the following manner:

pointWidth = pointSize threshold ⁢ pointSize >= threshold otherwise

The point alpha value is modified by computing:

pointAlpha = 1 pointSize threshold 2 ⁢ pointSize >= threshold otherwise

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 w + .5 y 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 w + .5 y 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 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 w y w. 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 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_SMOOTH_POINT_SIZE_RANGE and GL_SMOOTH_POINT_SIZE_GRANULARITY. For aliased points, query the supported ranges and granularity with glGet() with arguments GL_ALIASED_POINT_SIZE_RANGE.

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 specified value.

A 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 value.

GL_POINT_SIZE_RANGE and GL_POINT_SIZE_GRANULARITY are deprecated 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 execution of glEnd().

ASSOCIATED GETS

glGet() with argument GL_ALIASED_POINT_SIZE_RANGE

glGet() with argument GL_POINT_SIZE

glGet() with argument GL_POINT_SIZE_MIN

glGet() with argument GL_POINT_SIZE_MAX

glGet() with argument GL_POINT_FADE_THRESHOLD_SIZE

glGet() with argument GL_POINT_DISTANCE_ATTENUATION

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(), glPointParameter()

COPYRIGHT

Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.