# glBegin, glEnd

The **glBegin** and **glEnd** functions delimit the vertices of a primitive or a group of like primitives.

void glBegin( GLenum mode ); void glEnd( void );

#### Parameters

*mode*- The primitive or primitives that will be created from vertices presented between
**glBegin**and the subsequent**glEnd**. The following are accepted symbolic constants and their meanings:- 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*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.

#### Remarks

The **glBegin** and **glEnd** functions delimit the vertices that define a primitive or a group of like primitives. The **glBegin** function accepts a single argument that specifies which of ten primitives the vertices compose. Taking *n* as an integer count starting at one, and *N *as the total number of vertices specified, the interpretations are as follows:

- You can use only a subset of OpenGL functions between
**glBegin**and**glEnd**. The functions you can use are:**glVertex**

**glColor**

**glIndex**

**glNormal**

**glTexCoord**

**glEvalCoord**

**glEvalPoint**

**glMaterial**

**glEdgeFlag**You can also use

**glCallList**or**glCallLists**to execute display lists that include only the preceding functions. If any other OpenGL function is called between**glBegin**and**glEnd**, the error flag is set and the function is ignored. - Regardless of the value chosen for
*mode*in**glBegin**, there is no limit to the number of vertices you can define 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 complete primitives are drawn. - The minimum specification of vertices for each primitive is:

Minimum number of vertices | Type of primitive |
---|---|

1 | point |

2 | line |

3 | triangle |

4 | quadrilateral |

3 | polygon |

Modes that require a certain multiple of vertices are GL_LINES (2), GL_TRIANGLES (3), GL_QUADS (4), and GL_QUAD_STRIP (2).

#### Error Codes

The following are the error codes generated and their conditions.

Error code | Condition |
---|---|

GL_INVALID_ENUM | mode was set to an unaccepted value. |

GL_INVALID_OPERATION | A function other than glVertex, glColor, glIndex, glNormal, glTexCoord, glEvalCoord, glEvalPoint, glMaterial, glEdgeFlag, glCallList, or glCallLists was called between glBegin and the corresponding glEnd. The function glEnd was called before the corresponding glBegin was called, or glBegin was called within a glBegin/glEnd sequence. |

#### Requirements

** Windows NT/2000: **Requires Windows NT 3.5 or later.

** Windows 95/98: **Requires Windows 95 or later. Available as a redistributable for Windows 95.

** Header: **Declared in Gl.h.

** Library: **Use Opengl32.lib.

#### See Also

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