Index for Section 3G

Alphabetical listing for G

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glBegin(3G)
NAME
  glBegin, glEnd - delimit the vertices of a primitive or a group of like
  primglBeginitives

SYNOPSIS
  void glBegin(
	  GLenum mode );

  void glEnd(
	  void );

PARAMETERS
  mode
      Specifies the primitive or primitives that will be created from
      vertices presented between glBegin() and the subsequent glEnd(). Ten
      symbolic constants are accepted: GL_POINTS, GL_LINES, GL_LINE_STRIP,
      GL_LINE_LOOP, GL_TRIANGLES, GL_TRIANGLE_STRIP, GL_TRIANGLE_FAN,
      GL_QUADS, GL_QUAD_STRIP, and GL_POLYGON.

DESCRIPTION
  glBegin() and glEnd() delimit the vertices that define a primitive or a
  group of like primitives.  glBegin() accepts a single argument that
  specifies in which of ten ways the vertices are interpreted. Taking n as an
  integer count starting at one, and N as the total number of vertices
  specified, the interpretations are as follows:

  GL_POINTS
      Treats each vertex as a single point. Vertex n defines point n.  N
      points are drawn.

  GL_LINES
      Treats each pair of vertices as an independent line segment. Vertices
      2n-1 and 2n define line n.  N/2 lines are drawn.

  GL_LINE_STRIP
      Draws a connected group of line segments from the first vertex to the
      last. Vertices n and n+1 define line n.  N-1 lines are drawn.

  GL_LINE_LOOP
      Draws a connected group of line segments from the first vertex to the
      last, then back to the first. Vertices n and n+1 define line n. The
      last line, however, is defined by vertices N and 1.  N lines are drawn.

  GL_TRIANGLES
      Treats each triplet of vertices as an independent triangle. Vertices
      3n-2, 3n-1, and 3n define triangle n.  N/3 triangles are drawn.

  GL_TRIANGLE_STRIP
      Draws a connected group of triangles.  One triangle is defined for each
      vertex presented after the first two vertices.  For odd n, vertices n,
      n+1, and n+2 define triangle n.  For even n, vertices n+1, n, and n+2
      define triangle n.  N-2 triangles are drawn.

  GL_TRIANGLE_FAN
      Draws a connected group of triangles. One triangle is defined for each
      vertex presented after the first two vertices. Vertices 1, n+1, and n+2
      define triangle n.  N-2 triangles are drawn.

  GL_QUADS
      Treats each group of four vertices as an independent quadrilateral.
      Vertices 4n-3, 4n-2, 4n-1, and 4n define quadrilateral n.	 N/4
      quadrilaterals are drawn.

  GL_QUAD_STRIP
      Draws a connected group of quadrilaterals. One quadrilateral is defined
      for each pair of vertices presented after the first pair. Vertices 2n-
      1, 2n, 2n+2, and 2n+1 define quadrilateral n.  N/2-1 quadrilaterals are
      drawn. Note that the order in which vertices are used to construct a
      quadrilateral from strip data is different from that used with
      independent data.

  GL_POLYGON
      Draws a single, convex polygon. Vertices 1 through N define this
      polygon.

  Only a subset of GL commands can be used between glBegin() and glEnd(). The
  commands are glVertex(), glColor(), glIndex(), glNormal(), glTexCoord(),
  glEvalCoord(), glEvalPoint(), glArrayElement(), glMaterial(), and
  glEdgeFlag(). Also, it is acceptable to use glCallList() or glCallLists()
  to execute display lists that include only the preceding commands. If any
  other GL command is executed between glBegin() and glEnd(), the error
  option is set and the command is ignored.

  Regardless of the value chosen for mode, there is no limit to the number of
  vertices that can be defined between glBegin() and glEnd(). Lines,
  triangles, quadrilaterals, and polygons that are incompletely specified are
  not drawn. Incomplete specification results when either too few vertices
  are provided to specify even a single primitive or when an incorrect
  multiple of vertices is specified. The incomplete primitive is ignored; the
  rest are drawn.

  The minimum specification of vertices for each primitive is as follows: 1
  for a point, 2 for a line, 3 for a triangle, 4 for a quadrilateral, and 3
  for a polygon. Modes that require a certain multiple of vertices are
  GL_LINES (2), GL_TRIANGLES (3), GL_QUADS (4), and GL_QUAD_STRIP (2).

ERRORS
  GL_INVALID_ENUM is generated if mode is set to an unaccepted value.

  GL_INVALID_OPERATION is generated if glBegin() is executed between a
  glBegin() and the corresponding execution of glEnd().

  GL_INVALID_OPERATION is generated if glEnd() is executed without being
  preceded by a glBegin().

  GL_INVALID_OPERATION is generated if a command other than glVertex(),
  glColor(), glIndex(), glNormal(), glTexCoord(), glEvalCoord(),
  glEvalPoint(), glArrayElement(), glMaterial(), glEdgeFlag(), glCallList(),
  or glCallLists() is executed between the execution of glBegin() and the
  corresponding execution glEnd().

  Execution of glEnableClientState(), glDisableClientState(),
  glEdgeFlagPointer(), glTexCoordPointer(), glColorPointer(),
  glIndexPointer(), glNormalPointer(), glVertexPointer(),
  glInterleavedArrays(), or glPixelStore() is not allowed after a call to
  glBegin() and before the corresponding call to glEnd(), but an error may or
  may not be generated.

SEE ALSO
  glArrayElement(3), glCallList(3), glCallLists(), glColor(3), glEdgeFlag(3),
  glEvalCoord(3), glEvalPoint(3), glIndex(3), glMaterial(3), glNormal(3),
  glTexCoord(3), glVertex(3)

Index for Section 3G

Alphabetical listing for G

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