Name

glPointSize — specify the diameter of rasterized points

C Specification

void glPointSize(GLfloat size);
 
void glPointSizex(GLfixed 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.

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 xy of the pixel fragment that represents the point is computed as

[ xw ] + 12 [ yw ] + 12

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

[ xw + 12 ] [ yw + 12 ]

and the rasterized fragment's centers are the half-integer window coordinates within the square of the rounded size centered at xy . 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 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 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, call glGet with the argument GL_SMOOTH_POINT_SIZE_RANGE. For aliased points, query the supported ranges glGet with the argument GL_ALIASED_POINT_SIZE_RANGE.

Notes

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.

Errors

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

Associated Gets

glGet with argument GL_ALIASED_POINT_SIZE_RANGE

glGet with argument GL_SMOOTH_POINT_SIZE_RANGE

See Also

glEnable, glGet

Copyright

Copyright © 2003-2004 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.