GLBEGIN() GLBEGIN() NAME glBegin, glEnd - delimit the vertices of a primitive or a group of like primitives C SPECIFICATION void glBegin( GLenum mode ) PARAMETERS mode Specifies 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. 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 de- fines 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, how- ever, is defined by vertices N and 1. N lines are drawn. GL_TRIANGLES Treats each triplet of vertices as an independent tri- angle. 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 de- fine 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 de- fine 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 quadri- laterals are drawn. Note that the order in which ver- tices 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 ac- ceptable to use glCallList or glCallLists to execute display lists that in- clude only the preceding commands. If any other GL command is executed be- tween 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 ver- tices 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 pre- ceded by a glBegin. GL_INVALID_OPERATION is generated if a command other than glVertex, gl- Color, glIndex, glNormal, glTexCoord, glEvalCoord, glEvalPoint, glArrayEle- ment, glMaterial, glEdgeFlag, glCallList, or glCallLists is executed be- tween 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. SEE ALSO glArrayElement, glCallList, glCallLists, glColor, glEdgeFlag, glEvalCoord, glEvalPoint, glIndex, glMaterial, glNormal, glTexCoord, glVertex GLBEGIN()
NAME | C SPECIFICATION | PARAMETERS | C SPECIFICATION | DESCRIPTION | ERRORS | SEE ALSO
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