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<STRONG>NAME</STRONG>
<STRONG>glBegin,</STRONG> <STRONG>glEnd</STRONG> - delimit the vertices of a primitive or a
group of like primitives
<STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>
void <STRONG>glBegin</STRONG>( GLenum <EM>mode</EM> )
<STRONG>PARAMETERS</STRONG>
<EM>mode</EM> Specifies the primitive or primitives that will be
created from vertices presented between <STRONG>glBegin</STRONG> and
the subsequent <STRONG>glEnd</STRONG>. Ten symbolic constants are
accepted: <STRONG>GL_POINTS</STRONG>, <STRONG>GL_LINES</STRONG>, <STRONG>GL_LINE_STRIP</STRONG>,
<STRONG>GL_LINE_LOOP</STRONG>, <STRONG>GL_TRIANGLES</STRONG>, <STRONG>GL_TRIANGLE_STRIP</STRONG>,
<STRONG>GL_TRIANGLE_FAN</STRONG>, <STRONG>GL_QUADS</STRONG>, <STRONG>GL_QUAD_STRIP</STRONG>, and
<STRONG>GL_POLYGON</STRONG>.
<STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>
void <STRONG>glEnd</STRONG>( void )
<STRONG>DESCRIPTION</STRONG>
<STRONG>glBegin</STRONG> and <STRONG>glEnd</STRONG> delimit the vertices that define a
primitive or a group of like primitives. <STRONG>glBegin</STRONG> accepts a
single argument that specifies in which of ten ways the
vertices are interpreted. Taking <EM>n</EM> as an integer count
starting at one, and <EM>N</EM> as the total number of vertices
specified, the interpretations are as follows:
<STRONG>GL_POINTS</STRONG> Treats each vertex as a single point.
Vertex <EM>n</EM> defines point <EM>n</EM>. <EM>N</EM> points are
drawn.
<STRONG>GL_LINES</STRONG> Treats each pair of vertices as an
independent line segment. Vertices
<EM>2n</EM>-<EM>1</EM> and <EM>2n</EM> define line <EM>n</EM>. <EM>N</EM>/<EM>2</EM> lines
are drawn.
<STRONG>GL_LINE_STRIP</STRONG> Draws a connected group of line
segments from the first vertex to the
last. Vertices <EM>n</EM> and <EM>n</EM>+<EM>1</EM> define line
<EM>n</EM>. <EM>N</EM>-<EM>1</EM> lines are drawn.
<STRONG>GL_LINE_LOOP</STRONG> Draws a connected group of line
segments from the first vertex to the
last, then back to the first. Vertices
<EM>n</EM> and <EM>n</EM>+<EM>1</EM> define line <EM>n</EM>. The last
line, however, is defined by vertices <EM>N</EM>
and <EM>1</EM>. <EM>N</EM> lines are drawn.
<STRONG>GL_TRIANGLES</STRONG> Treats each triplet of vertices as an
independent triangle. Vertices <EM>3n</EM>-<EM>2</EM>,
<EM>3n</EM>-<EM>1</EM>, and <EM>3n</EM> define triangle <EM>n</EM>. <EM>N</EM>/<EM>3</EM>
triangles are drawn.
<STRONG>GL_TRIANGLE_STRIP</STRONG> Draws a connected group of triangles.
One triangle is defined for each vertex
presented after the first two vertices.
For odd <EM>n</EM>, vertices <EM>n</EM>, <EM>n</EM>+<EM>1</EM>, and <EM>n</EM>+<EM>2</EM>
define triangle <EM>n</EM>. For even <EM>n</EM>,
vertices <EM>n</EM>+<EM>1</EM>, <EM>n</EM>, and <EM>n</EM>+<EM>2</EM> define
triangle <EM>n</EM>. <EM>N</EM>-<EM>2</EM> triangles are drawn.
<STRONG>GL_TRIANGLE_FAN</STRONG> Draws a connected group of triangles.
One triangle is defined for each vertex
presented after the first two vertices.
Vertices <EM>1</EM>, <EM>n</EM>+<EM>1</EM>, and <EM>n</EM>+<EM>2</EM> define
triangle <EM>n</EM>. <EM>N</EM>-<EM>2</EM> triangles are drawn.
<STRONG>GL_QUADS</STRONG> Treats each group of four vertices as
an independent quadrilateral. Vertices
<EM>4n</EM>-<EM>3</EM>, <EM>4n</EM>-<EM>2</EM>, <EM>4n</EM>-<EM>1</EM>, and <EM>4n</EM> define
quadrilateral <EM>n</EM>. <EM>N</EM>/<EM>4</EM> quadrilaterals
are drawn.
<STRONG>GL_QUAD_STRIP</STRONG> Draws a connected group of
quadrilaterals. One quadrilateral is
defined for each pair of vertices
presented after the first pair.
Vertices <EM>2n</EM>-<EM>1</EM>, <EM>2n</EM>, <EM>2n</EM>+<EM>2</EM>, and <EM>2n</EM>+<EM>1</EM>
define quadrilateral <EM>n</EM>. <EM>N</EM>/<EM>2</EM>-<EM>1</EM>
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.
<STRONG>GL_POLYGON</STRONG> Draws a single, convex polygon.
Vertices <EM>1</EM> through <EM>N</EM> define this
polygon.
Only a subset of GL commands can be used between <STRONG>glBegin</STRONG> and
<STRONG>glEnd</STRONG>. The commands are <STRONG>glVertex</STRONG>, <STRONG>glColor</STRONG>, <STRONG>glIndex</STRONG>,
<STRONG>glNormal</STRONG>, <STRONG>glTexCoord</STRONG>, <STRONG>glEvalCoord</STRONG>, <STRONG>glEvalPoint</STRONG>,
<STRONG>glArrayElement</STRONG>, <STRONG>glMaterial</STRONG>, and <STRONG>glEdgeFlag</STRONG>. Also, it is
acceptable to use <STRONG>glCallList</STRONG> or <STRONG>glCallLists</STRONG> to execute
display lists that include only the preceding commands. If
any other GL command is executed between <STRONG>glBegin</STRONG> and <STRONG>glEnd</STRONG>,
the error flag is set and the command is ignored.
Regardless of the value chosen for <EM>mode</EM>, there is no limit
to the number of vertices that can be defined between
<STRONG>glBegin</STRONG> and <STRONG>glEnd</STRONG>. 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 <STRONG>GL_LINES</STRONG> (2),
<STRONG>GL_TRIANGLES</STRONG> (3), <STRONG>GL_QUADS</STRONG> (4), and <STRONG>GL_QUAD_STRIP</STRONG> (2).
<STRONG>ERRORS</STRONG>
<STRONG>GL_INVALID_ENUM</STRONG> is generated if <EM>mode</EM> is set to an unaccepted
value.
<STRONG>GL_INVALID_OPERATION</STRONG> is generated if <STRONG>glBegin</STRONG> is executed
between a <STRONG>glBegin</STRONG> and the corresponding execution of <STRONG>glEnd</STRONG>.
<STRONG>GL_INVALID_OPERATION</STRONG> is generated if <STRONG>glEnd</STRONG> is executed
without being preceded by a <STRONG>glBegin</STRONG>.
<STRONG>GL_INVALID_OPERATION</STRONG> is generated if a command other than
<STRONG>glVertex</STRONG>, <STRONG>glColor</STRONG>, <STRONG>glIndex</STRONG>, <STRONG>glNormal</STRONG>, <STRONG>glTexCoord</STRONG>,
<STRONG>glEvalCoord</STRONG>, <STRONG>glEvalPoint</STRONG>, <STRONG>glArrayElement</STRONG>, <STRONG>glMaterial</STRONG>,
<STRONG>glEdgeFlag</STRONG>, <STRONG>glCallList</STRONG>, or <STRONG>glCallLists</STRONG> is executed between
the execution of <STRONG>glBegin</STRONG> and the corresponding execution
<STRONG>glEnd</STRONG>.
Execution of <STRONG>glEnableClientState</STRONG>, <STRONG>glDisableClientState</STRONG>,
<STRONG>glEdgeFlagPointer</STRONG>, <STRONG>glTexCoordPointer</STRONG>, <STRONG>glColorPointer</STRONG>,
<STRONG>glIndexPointer</STRONG>, <STRONG>glNormalPointer</STRONG>,
<STRONG>glVertexPointer</STRONG>, <STRONG>glInterleavedArrays</STRONG>, or <STRONG>glPixelStore</STRONG> is not
allowed after a call to <STRONG>glBegin</STRONG> and before the corresponding
call to <STRONG>glEnd</STRONG>, but an error may or may not be generated.
<STRONG>SEE</STRONG> <STRONG>ALSO</STRONG>
<STRONG>glArrayElement</STRONG>, <STRONG>glCallList</STRONG>, <STRONG>glCallLists</STRONG>, <STRONG>glColor</STRONG>,
<STRONG>glEdgeFlag</STRONG>, <STRONG>glEvalCoord</STRONG>,
<STRONG>glEvalPoint</STRONG>, <STRONG>glIndex</STRONG>, <STRONG>glMaterial</STRONG>, <STRONG>glNormal</STRONG>, <STRONG>glTexCoord</STRONG>,
<STRONG>glVertex</STRONG>
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