 OpenGL man pages 

glBegin.3gl





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
        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 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  Treates 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
            Treates 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, 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 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.


See Also

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






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Last Edited: Fri Dec 6 11:18:03 EST 1996 by AFV 
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