Linux Manual Pages

Free Software * Books

Source Code

Free Media

Linux

GLBEGIN

NAME
C SPECIFICATION
PARAMETERS
C SPECIFICATION
DESCRIPTION
ERRORS
SEE ALSO

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 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 $n$ 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 $n$. $N/2^-^1$ 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, glArrayElement, 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 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, glEvalPoint, glArrayElement, glMaterial, glEdgeFlag, glCallList, or glCallLists is executed between 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.

Opportunity

Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.

Education

Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.