glBegin(3G) glBegin(3G)[top]NAMEglBegin, glEnd - delimit the vertices of a primitive or a group of like primglBeginitivesSYNOPSISvoid glBegin( GLenum mode ); void glEnd( void );PARAMETERSSpecifies the primitive or primitives that will be created from ver‐ tices presented between glBegin() and the subsequent glEnd(). Ten sym‐ bolic 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.DESCRIPTIONglBegin() 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 ver‐ tices specified, the interpretations are as follows: Treats each vertex as a single point. Vertex n defines point n. N points are drawn. Treats each pair of vertices as an independent line segment. Vertices 2n-1 and 2n define line n. N/2 lines are drawn. 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. 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. Treats each triplet of vertices as an independent triangle. Vertices 3n-2, 3n-1, and 3n define triangle n. N/3 triangles are drawn. 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. Draws a connected group of triangles. One triangle is defined for each vertex presented after the first two ver‐ tices. Vertices 1, n+1, and n+2 define triangle n. N-2 triangles are drawn. Treats each group of four vertices as an independent quadrilat‐ eral. Vertices 4n-3, 4n-2, 4n-1, and 4n define quadrilateral n. N/4 quadrilaterals are drawn. 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 ver‐ tices are used to construct a quadrilateral from strip data is differ‐ ent from that used with independent data. Draws a single, convex poly‐ gon. 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(), glTexCo‐ ord(), glEvalCoord(), glEvalPoint(), glArrayElement(), glMaterial(), and glEdgeFlag(). Also, it is acceptable to use glCallList() or glCall‐ Lists() to execute display lists that include only the preceding com‐ mands. If any other GL command is executed between glBegin() and glEnd(), the error option is set and the command is ignored. Regardless of the value chosen for mode, there is no limit to the num‐ ber 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).ERRORSGL_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(), glEval‐ Point(), glArrayElement(), glMaterial(), glEdgeFlag(), glCallList(), or glCallLists() is executed between the execution of glBegin() and the corresponding execution glEnd(). Execution of glEnableClientState(), glDisableClientState(), glEdgeFlag‐ Pointer(), glTexCoordPointer(), glColorPointer(), glIndexPointer(), glNormalPointer(), glVertexPointer(), glInterleavedArrays(), or glPix‐ elStore() is not allowed after a call to glBegin() and before the cor‐ responding call to glEnd(), but an error may or may not be generated.SEE ALSOglArrayElement(3), glCallList(3), glCallLists(), glColor(3), glEdge‐ Flag(3), glEvalCoord(3), glEvalPoint(3), glIndex(3), glMaterial(3), glNormal(3), glTexCoord(3), glVertex(3) glBegin(3G)

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