glPointSize.3gl

Name

  glPointSize -	specify	the diameter of	rasterized points

C Specification

  void glPointSize( GLfloat size )

Parameters

  size	Specifies the diameter of rasterized points.  The default is 1.0.

Description

  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
  GL_POINT_SMOOTH.

  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 )
			     w	           w

  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) )
			     w	           w

  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
    w   w
  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.

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.

  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 zero.

  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_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, glPointSmooth

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Last Edited: Fri Dec 6 11:18:03 EST 1996 by AFV
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