glBegin, glEnd - delimit the vertices	of a primitive or a
group	of like	primitives

glBegin
	glBegin(mode) -> None
glEnd
	glEnd() -> None

void glBegin(	GLenum mode )

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.

void glEnd( void )

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 flag 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).

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.

glArrayElement, glCallList, glCallLists, glColor,
glEdgeFlag, glEvalCoord,
glEvalPoint, glIndex,	glMaterial, glNormal, glTexCoord,
glVertex