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OpenGL 1.2 for AIX: Reference Manual
glBegin or glEnd Subroutine
Purpose
Delimits the vertices of a primitive or
group of like primitives.
Library
OpenGL C bindings library:
libGL.a
C Syntax
void glBegin(GLenum mode)
void glEnd(void)
Description
The glBegin and glEnd
subroutines delimit the vertices that define a primitive or group of like
primitives. The glBegin subroutine accepts a single argument that
specifies which of 10 ways the vertices will be interpreted. Taking n as
an integer count starting at 1 (one), and N as the total number of
vertices specified, the interpretations are:
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 subroutines can be used
between the glBegin and glEnd subroutines. The subroutines are:
glVertex, glColor, glIndex, glNormal,
glTexCoord, glEvalCoord, glEvalPoint, glMaterial,
and glEdgeFlag. Also, it is acceptable to use glCallList or
glCallLists to execute display lists that include only the preceding
subroutines. If any other GL subroutine is called between the glBegin and
glEnd subroutines, the error flag is set and the subroutine is ignored.
Regardless of the value chosen for mode,
there is no limit to the number of vertices that can be defined between the
glBegin and glEnd subroutines. 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).
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. |
Errors
INVALID_ENUM |
Indicates that mode is set to an unaccepted value. |
GL_INVALID_OPERATION |
Indicates that a subroutine other than glVertex,
glColor, glIndex, glNormal, glTexCoord,
glEvalCoord, glEvalPoint, glMaterial, glEdgeFlag,
glCallList, or glCallLists subroutine is called between
glBegin and the corresponding glEnd. |
GL_INVALID_OPERATION |
Indicates that glEnd is called before the corresponding
glBegin is called. |
Files
/usr/include/GL/gl.h |
Contains C language constants, variable type definitions, and ANSI function
prototypes for OpenGL. |
Related Information
The
glArrayElement subroutine,
glArrayElementEXT subroutine,
glColor subroutine,
glCallList subroutine,
glCallLists subroutine,
glEdgeFlag subroutine,
glEvalCoord subroutine,
glEvalPoint subroutine,
glIndex subroutine,
glMaterial subroutine,
glNormal subroutine,
glTexCoord subroutine,
glVertex subroutine.
OpenGL Overview.
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