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GLBEGIN(3G)				  OpenGL Manual 			      GLBEGIN(3G)

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

C SPECIFICATION
       void glBegin(GLenum mode);

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.

C SPECIFICATION
       void glEnd(void);

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 2  n - 1 and 2
	   n 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 3  n - 2, 3  n -
	   1, and 3  n 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 4  n - 3,
	   4  n - 2, 4	n - 1, and 4  n 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 2  n - 1, 2  n, 2  n + 2, and 2
	   n + 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(), glSecondaryColor(), glIndex(), glNormal(), glFogCoord(),
       glTexCoord(), glMultiTexCoord(), glVertexAttrib(), 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).

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(),
       glSecondaryColor(), glIndex(), glNormal(), glFogCoord(), glTexCoord(), glMultiTexCoord(),
       glVertexAttrib(), 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(),
       glFogCoordPointer(), glTexCoordPointer(), glColorPointer(), glSecondaryColorPointer(),
       glIndexPointer(), glNormalPointer(), glVertexPointer(), glVertexAttribPointer(),
       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(), glCallList(), glCallLists(), glColor(), glEdgeFlag(), glEvalCoord(),
       glEvalPoint(), glFogCoord(), glIndex(), glMaterial(), glMultiTexCoord(), glNormal(),
       glSecondaryColor(), glTexCoord(), glVertex(), glVertexAttrib()

COPYRIGHT
       Copyright (C) 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/.

AUTHORS
       opengl.org

opengl.org				    06/10/2014				      GLBEGIN(3G)
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