glBegin, glEnd - delimit the vertices of a primitive or a group of like primitives

void glBegin( GLenummode)

modeSpecifies 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.

void glEnd( void )

glBegin and glEnd delimit the vertices that define a primitive or a group of like primitives. glBegin accepts a single argument that specifies which of ten ways the vertices are interpreted. Takingnas an integer count starting at one, andNas the total number of vertices specified, the interpretations are as follows: GL_POINTS Treats each vertex as a single point. Vertexndefines pointn.Npoints are drawn. GL_LINES Treates each pair of vertices as an independent line segment. Vertices2n-1and2ndefine linen.N/2lines are drawn. GL_LINE_STRIP Draws a connected group of line segments from the first vertex to the last. Verticesnandn+1define linen.N-1lines are drawn. GL_LINE_LOOP Draws a connected group of line segments from the first vertex to the last, then back to the first. Verticesnandn+1define linen. The last line, however, is defined by verticesNand1.Nlines are drawn. GL_TRIANGLES Treates each triplet of vertices as an independent triangle. Vertices3n-2,3n-1, and3ndefine trianglen.N/3triangles 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 oddn, verticesn,n+1, andn+2define trianglen. For evenn, verticesn+1,n, andn+2define trianglen.N-2triangles are drawn. GL_TRIANGLE_FAN Draws a connected group of triangles. One triangle is defined for each vertex presented after the first two vertices. Vertices1,n+1, andn+2define trianglen.N-2triangles are drawn. GL_QUADS Treats each group of four vertices as an independent quadrilateral. Vertices4n-3,4n-2,4n-1, and4ndefine quadrilateraln.N/4quadrilaterals 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. Vertices2n-1,2n,2n+2, and2n+1define quadrilateraln.N/2-1quadrilaterals 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. Vertices1throughNdefine 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, 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 formode, 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).

GL_INVALID_ENUM is generated ifmodeis set to an unaccepted value. GL_INVALID_OPERATION is generated if a command other than glVertex, glColor, glIndex, glNormal, glTexCoord, glEvalCoord, glEvalPoint, glMaterial, glEdgeFlag, glCallList, or glCallLists is executed between glBegin and the corresponding glEnd. GL_INVALID_OPERATION is generated if a 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.

glCallList, glCallLists, glColor, glEdgeFlag, glEvalCoord, glEvalPoint, glIndex, glMaterial, glNormal, glTexCoord, glVertex

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Fri Dec 6 11:18:03 EST 1996
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