NAME
glBegin, glEnd
- delimit the vertices of a primitive or a group of like primitives
C SPECIFICATION
void ggllBBeeggiinn(
GLenum _m_o_d_e )
delim $$
PARAMETERS
-
_m_o_d_e
-
Specifies the primitive or primitives that will be created from vertices
presented between ggllBBeeggiinn and the subsequent ggllEEnndd.
Ten symbolic constants are accepted:
GGLL__PPOOIINNTTSS,
GGLL__LLIINNEESS,
GGLL__LLIINNEE__SSTTRRIIPP,
GGLL__LLIINNEE__LLOOOOPP,
GGLL__TTRRIIAANNGGLLEESS,
GGLL__TTRRIIAANNGGLLEE__SSTTRRIIPP,
GGLL__TTRRIIAANNGGLLEE__FFAANN,
GGLL__QQUUAADDSS,
GGLL__QQUUAADD__SSTTRRIIPP, and
GGLL__PPOOLLYYGGOONN.
C SPECIFICATION
void ggllEEnndd( void )
DESCRIPTION
ggllBBeeggiinn and ggllEEnndd delimit the vertices that define a primitive or
a group of like primitives.
ggllBBeeggiinn 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:
-
GGLL__PPOOIINNTTSS
-
Treats each vertex as a single point.
Vertex $n$ defines point $n$.
$N$ points are drawn.
-
GGLL__LLIINNEESS
-
Treats each pair of vertices as an independent line segment.
Vertices $2n^-^1$ and $2n$ define line $n$.
$N/2$ lines are drawn.
-
GGLL__LLIINNEE__SSTTRRIIPP
-
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.
-
GGLL__LLIINNEE__LLOOOOPP
-
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.
-
GGLL__TTRRIIAANNGGLLEESS
-
Treats each triplet of vertices as an independent triangle.
Vertices $3n^-^2$, $3n^-^1$, and $3n$ define triangle $n$.
$N/3$ triangles are drawn.
-
GGLL__TTRRIIAANNGGLLEE__SSTTRRIIPP
-
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.
-
GGLL__TTRRIIAANNGGLLEE__FFAANN
-
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.
-
GGLL__QQUUAADDSS
-
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.
-
GGLL__QQUUAADD__SSTTRRIIPP
-
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.
-
GGLL__PPOOLLYYGGOONN
-
Draws a single,
convex polygon.
Vertices $1$ through $N$ define this polygon.
Only a subset of GL commands can be used between ggllBBeeggiinn and ggllEEnndd.
The commands are
ggllVVeerrtteexx,
ggllCCoolloorr,
ggllIInnddeexx,
ggllNNoorrmmaall,
ggllTTeexxCCoooorrdd,
ggllEEvvaallCCoooorrdd,
ggllEEvvaallPPooiinntt,
ggllAArrrraayyEElleemmeenntt,
ggllMMaatteerriiaall, and
ggllEEddggeeFFllaagg.
Also,
it is acceptable to use
ggllCCaallllLLiisstt or
ggllCCaallllLLiissttss to execute
display lists that include only the preceding commands.
If any other GL command is executed between ggllBBeeggiinn and ggllEEnndd,
the error flag is set and the command is ignored.
Regardless of the value chosen for _m_o_d_e,
there is no limit to the number of vertices that can be defined
between ggllBBeeggiinn and ggllEEnndd.
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
GGLL__LLIINNEESS (2),
GGLL__TTRRIIAANNGGLLEESS (3),
GGLL__QQUUAADDSS (4),
and GGLL__QQUUAADD__SSTTRRIIPP (2).
ERRORS
GGLL__IINNVVAALLIIDD__EENNUUMM is generated if _m_o_d_e is set to an unaccepted value.
GGLL__IINNVVAALLIIDD__OOPPEERRAATTIIOONN is generated if ggllBBeeggiinn is executed between a
ggllBBeeggiinn
and the corresponding execution of ggllEEnndd.
GGLL__IINNVVAALLIIDD__OOPPEERRAATTIIOONN is generated if ggllEEnndd is executed without being
preceded by a ggllBBeeggiinn.
GGLL__IINNVVAALLIIDD__OOPPEERRAATTIIOONN is generated if a command other than
ggllVVeerrtteexx,
ggllCCoolloorr,
ggllIInnddeexx,
ggllNNoorrmmaall,
ggllTTeexxCCoooorrdd,
ggllEEvvaallCCoooorrdd,
ggllEEvvaallPPooiinntt,
ggllAArrrraayyEElleemmeenntt,
ggllMMaatteerriiaall,
ggllEEddggeeFFllaagg,
ggllCCaallllLLiisstt, or
ggllCCaallllLLiissttss is executed between
the execution of ggllBBeeggiinn and the corresponding
execution ggllEEnndd.
Execution of
ggllEEnnaabblleeCClliieennttSSttaattee,
ggllDDiissaabblleeCClliieennttSSttaattee,
ggllEEddggeeFFllaaggPPooiinntteerr,
ggllTTeexxCCoooorrddPPooiinntteerr,
ggllCCoolloorrPPooiinntteerr,
ggllIInnddeexxPPooiinntteerr,
ggllNNoorrmmaallPPooiinntteerr,
ggllVVeerrtteexxPPooiinntteerr,
ggllIInntteerrlleeaavveeddAArrrraayyss, or
ggllPPiixxeellSSttoorree is not allowed after a call to ggllBBeeggiinn and before
the corresponding call to ggllEEnndd,
but an error may or may not be generated.
SEE ALSO
ggllAArrrraayyEElleemmeenntt((33GG)),
ggllCCaallllLLiisstt((33GG)),
ggllCCaallllLLiissttss((33GG)),
ggllCCoolloorr((33GG)),
ggllEEddggeeFFllaagg((33GG)),
ggllEEvvaallCCoooorrdd((33GG)),
ggllEEvvaallPPooiinntt((33GG)),
ggllIInnddeexx((33GG)),
ggllMMaatteerriiaall((33GG)),
ggllNNoorrmmaall((33GG)),
ggllTTeexxCCoooorrdd((33GG)),
ggllVVeerrtteexx((33GG))