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)