Интерактивная система просмотра системных руководств (man-ов)
glBegin (3)
>> glBegin (3) ( Разные man: Библиотечные вызовы )
NAME
glBegin, glEnd
- delimit the vertices of a primitive or a group of like primitives
C SPECIFICATION
void glBegin(
GLenum mode )
delim $$
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 $2n^-^1$ 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 commands can be used between glBegin and glEnd.
The commands are
glVertex,
glColor,
glIndex,
glNormal,
glTexCoord,
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,
glIndex,
glNormal,
glTexCoord,
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,
glTexCoordPointer,
glColorPointer,
glIndexPointer,
glNormalPointer,
glVertexPointer,
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.
