<div class="refentry" lang="en" xml:lang="en"><a id="glBegin"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glBegin — delimit the vertices of a primitive or a group of like primitives</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table><tr><td><code class="funcdef">void <b class="fsfunc">glBegin</b>(</code></td><td>GLenum  </td><td><var class="pdparam">mode</var><code>)</code>;</td></tr></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>mode</code></em></span></dt><dd><p>

Specifies the primitive or primitives that will be created from vertices

presented between <code class="function">glBegin</code> and the subsequent <a class="citerefentry" href="glEnd"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>.

Ten symbolic constants are accepted:

<code class="constant">GL_POINTS</code>,

<code class="constant">GL_LINES</code>,

<code class="constant">GL_LINE_STRIP</code>,

<code class="constant">GL_LINE_LOOP</code>,

<code class="constant">GL_TRIANGLES</code>,

<code class="constant">GL_TRIANGLE_STRIP</code>,

<code class="constant">GL_TRIANGLE_FAN</code>,

<code class="constant">GL_QUADS</code>,

<code class="constant">GL_QUAD_STRIP</code>, and

<code class="constant">GL_POLYGON</code>.

</p></dd></dl></div></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table><tr><td><code class="funcdef">void <b class="fsfunc">glEnd</b>(</code></td><td> </td><td><var class="pdparam">void</var><code>)</code>;</td></tr></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>

<code class="function">glBegin</code> and <a class="citerefentry" href="glEnd"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a> delimit the vertices that define a primitive or

a group of like primitives.

<code class="function">glBegin</code> accepts a single argument that specifies in which of ten ways the

vertices are interpreted.

Taking

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>

as an integer count starting at one,

and

<math overflow="scroll"><mi mathvariant="italic">N</mi></math>

as the total number of vertices specified,

the interpretations are as follows:

</p><div class="variablelist"><dl><dt><span class="term"><code class="constant">GL_POINTS</code></span></dt><dd><p>

Treats each vertex as a single point.

Vertex

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>

defines point

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>.

<math overflow="scroll"><mi mathvariant="italic">N</mi></math>

points are drawn.

</p></dd><dt><span class="term"><code class="constant">GL_LINES</code></span></dt><dd><p>

Treats each pair of vertices as an independent line segment.

Vertices

<math overflow="scroll">

<mrow>

<mn>2</mn>

<mo>⁢</mo>

<mi mathvariant="italic">n</mi>

<mo>-</mo>

<mn>1</mn>

</mrow>

</math>

and

<math overflow="scroll">

<mrow>

<mn>2</mn>

<mo>⁢</mo>

<mi mathvariant="italic">n</mi>

</mrow>

</math>

define line

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>.

<math overflow="scroll">

<mfrac>

<mi mathvariant="italic">N</mi>

<mn>2</mn>

</mfrac>

</math>

lines are drawn.

</p></dd><dt><span class="term"><code class="constant">GL_LINE_STRIP</code></span></dt><dd><p>

Draws a connected group of line segments from the first vertex

to the last.

Vertices

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>

and

<math overflow="scroll">

<mrow>

<mi mathvariant="italic">n</mi>

<mo>+</mo>

<mn>1</mn>

</mrow>

</math>

define line

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>.

<math overflow="scroll">

<mrow>

<mi mathvariant="italic">N</mi>

<mo>-</mo>

<mn>1</mn>

</mrow>

</math>

lines are drawn.

</p></dd><dt><span class="term"><code class="constant">GL_LINE_LOOP</code></span></dt><dd><p>

Draws a connected group of line segments from the first vertex

to the last,

then back to the first.

Vertices

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>

and

<math overflow="scroll">

<mrow>

<mi mathvariant="italic">n</mi>

<mo>+</mo>

<mn>1</mn>

</mrow>

</math>

define line

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>.

The last line, however, is defined by vertices

<math overflow="scroll"><mi mathvariant="italic">N</mi></math>

and

<math overflow="scroll">

<mn>1</mn>

</math>.

<math overflow="scroll"><mi mathvariant="italic">N</mi></math>

lines are drawn.

</p></dd><dt><span class="term"><code class="constant">GL_TRIANGLES</code></span></dt><dd><p>

Treats each triplet of vertices as an independent triangle.

Vertices

<math overflow="scroll">

<mrow>

<mn>3</mn>

<mo>⁢</mo>

<mi mathvariant="italic">n</mi>

<mo>-</mo>

<mn>2</mn>

</mrow>

</math>,

<math overflow="scroll">

<mrow>

<mn>3</mn>

<mo>⁢</mo>

<mi mathvariant="italic">n</mi>

<mo>-</mo>

<mn>1</mn>

</mrow>

</math>,

and

<math overflow="scroll">

<mrow>

<mn>3</mn>

<mo>⁢</mo>

<mi mathvariant="italic">n</mi>

</mrow>

</math>

define triangle

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>.

<math overflow="scroll">

<mfrac>

<mi mathvariant="italic">N</mi>

<mn>3</mn>

</mfrac>

</math>

triangles are drawn.

</p></dd><dt><span class="term"><code class="constant">GL_TRIANGLE_STRIP</code></span></dt><dd><p>

Draws a connected group of triangles. One triangle is defined for each

vertex presented after the first two vertices. For odd

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>,

vertices

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>,

<math overflow="scroll">

<mrow>

<mi mathvariant="italic">n</mi>

<mo>+</mo>

<mn>1</mn>

</mrow>

</math>,

and

<math overflow="scroll">

<mrow>

<mi mathvariant="italic">n</mi>

<mo>+</mo>

<mn>2</mn>

</mrow>

</math>

define triangle

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>.

For even

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>,

vertices

<math overflow="scroll">

<mrow>

<mi mathvariant="italic">n</mi>

<mo>+</mo>

<mn>1</mn>

</mrow>

</math>,

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>,

and

<math overflow="scroll">

<mrow>

<mi mathvariant="italic">n</mi>

<mo>+</mo>

<mn>2</mn>

</mrow>

</math>

define triangle

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>.

<math overflow="scroll">

<mrow>

<mi mathvariant="italic">N</mi>

<mo>-</mo>

<mn>2</mn>

</mrow>

</math>

triangles are

drawn.

</p></dd><dt><span class="term"><code class="constant">GL_TRIANGLE_FAN</code></span></dt><dd><p>

Draws a connected group of triangles.

One triangle is defined for each vertex presented after the first two vertices.

Vertices

<math overflow="scroll">

<mn>1</mn>

</math>,

<math overflow="scroll">

<mrow>

<mi mathvariant="italic">n</mi>

<mo>+</mo>

<mn>1</mn>

</mrow>

</math>,

and

<math overflow="scroll">

<mrow>

<mi mathvariant="italic">n</mi>

<mo>+</mo>

<mn>2</mn>

</mrow>

</math>

define triangle

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>.

<math overflow="scroll">

<mrow>

<mi mathvariant="italic">N</mi>

<mo>-</mo>

<mn>2</mn>

</mrow>

</math>

triangles are drawn.

</p></dd><dt><span class="term"><code class="constant">GL_QUADS</code></span></dt><dd><p>

Treats each group of four vertices as an independent quadrilateral.

Vertices

<math overflow="scroll">

<mrow>

<mn>4</mn>

<mo>⁢</mo>

<mi mathvariant="italic">n</mi>

<mo>-</mo>

<mn>3</mn>

</mrow>

</math>,

<math overflow="scroll">

<mrow>

<mn>4</mn>

<mo>⁢</mo>

<mi mathvariant="italic">n</mi>

<mo>-</mo>

<mn>2</mn>

</mrow>

</math>,

<math overflow="scroll">

<mrow>

<mn>4</mn>

<mo>⁢</mo>

<mi mathvariant="italic">n</mi>

<mo>-</mo>

<mn>1</mn>

</mrow>

</math>,

and

<math overflow="scroll">

<mrow>

<mn>4</mn>

<mo>⁢</mo>

<mi mathvariant="italic">n</mi>

</mrow>

</math>

define quadrilateral

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>.

<math overflow="scroll">

<mfrac>

<mi mathvariant="italic">N</mi>

<mn>4</mn>

</mfrac>

</math>

quadrilaterals are drawn.

</p></dd><dt><span class="term"><code class="constant">GL_QUAD_STRIP</code></span></dt><dd><p>

Draws a connected group of quadrilaterals.

One quadrilateral is defined for each pair of vertices presented

after the first pair.

Vertices

<math overflow="scroll">

<mrow>

<mn>2</mn>

<mo>⁢</mo>

<mi mathvariant="italic">n</mi>

<mo>-</mo>

<mn>1</mn>

</mrow>

</math>,

<math overflow="scroll">

<mrow>

<mn>2</mn>

<mo>⁢</mo>

<mi mathvariant="italic">n</mi>

</mrow>

</math>,

<math overflow="scroll">

<mrow>

<mn>2</mn>

<mo>⁢</mo>

<mi mathvariant="italic">n</mi>

<mo>+</mo>

<mn>2</mn>

</mrow>

</math>,

and

<math overflow="scroll">

<mrow>

<mn>2</mn>

<mo>⁢</mo>

<mi mathvariant="italic">n</mi>

<mo>+</mo>

<mn>1</mn>

</mrow>

</math>

define quadrilateral

<math overflow="scroll"><mi mathvariant="italic">n</mi></math>.

<math overflow="scroll">

<mrow>

<mfrac>

<mi mathvariant="italic">N</mi>

<mn>2</mn>

</mfrac>

<mo>-</mo>

<mn>1</mn>

</mrow>

</math>

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.

</p></dd><dt><span class="term"><code class="constant">GL_POLYGON</code></span></dt><dd><p>

Draws a single,

convex polygon.

Vertices

<math overflow="scroll">

<mn>1</mn>

</math>

through

<math overflow="scroll"><mi mathvariant="italic">N</mi></math>

define this polygon.

</p></dd></dl></div><p>

Only a subset of GL commands can be used between <code class="function">glBegin</code> and <a class="citerefentry" href="glEnd"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>.

The commands are

<a class="citerefentry" href="glVertex"><span class="citerefentry"><span class="refentrytitle">glVertex</span></span></a>,

<a class="citerefentry" href="glColor"><span class="citerefentry"><span class="refentrytitle">glColor</span></span></a>,

<a class="citerefentry" href="glSecondaryColor"><span class="citerefentry"><span class="refentrytitle">glSecondaryColor</span></span></a>,

<a class="citerefentry" href="glIndex"><span class="citerefentry"><span class="refentrytitle">glIndex</span></span></a>,

<a class="citerefentry" href="glNormal"><span class="citerefentry"><span class="refentrytitle">glNormal</span></span></a>,

<a class="citerefentry" href="glFogCoord"><span class="citerefentry"><span class="refentrytitle">glFogCoord</span></span></a>,

<a class="citerefentry" href="glTexCoord"><span class="citerefentry"><span class="refentrytitle">glTexCoord</span></span></a>,

<a class="citerefentry" href="glMultiTexCoord"><span class="citerefentry"><span class="refentrytitle">glMultiTexCoord</span></span></a>,

<a class="citerefentry" href="glVertexAttrib"><span class="citerefentry"><span class="refentrytitle">glVertexAttrib</span></span></a>,

<a class="citerefentry" href="glEvalCoord"><span class="citerefentry"><span class="refentrytitle">glEvalCoord</span></span></a>,

<a class="citerefentry" href="glEvalPoint"><span class="citerefentry"><span class="refentrytitle">glEvalPoint</span></span></a>,

<a class="citerefentry" href="glArrayElement"><span class="citerefentry"><span class="refentrytitle">glArrayElement</span></span></a>,

<a class="citerefentry" href="glMaterial"><span class="citerefentry"><span class="refentrytitle">glMaterial</span></span></a>, and

<a class="citerefentry" href="glEdgeFlag"><span class="citerefentry"><span class="refentrytitle">glEdgeFlag</span></span></a>.

Also,

it is acceptable to use

<a class="citerefentry" href="glCallList"><span class="citerefentry"><span class="refentrytitle">glCallList</span></span></a> or

<a class="citerefentry" href="glCallLists"><span class="citerefentry"><span class="refentrytitle">glCallLists</span></span></a> to execute

display lists that include only the preceding commands.

If any other GL command is executed between <code class="function">glBegin</code> and <a class="citerefentry" href="glEnd"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>,

the error flag is set and the command is ignored.

</p><p>

Regardless of the value chosen for <em class="parameter"><code>mode</code></em>,

there is no limit to the number of vertices that can be defined

between <code class="function">glBegin</code> and <a class="citerefentry" href="glEnd"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>.

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.

</p><p>

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

<code class="constant">GL_LINES</code> (2),

<code class="constant">GL_TRIANGLES</code> (3),

<code class="constant">GL_QUADS</code> (4),

and <code class="constant">GL_QUAD_STRIP</code> (2).

</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p>

<code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>mode</code></em> is set to an unaccepted value.

</p><p>

<code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glBegin</code> is executed between a

<code class="function">glBegin</code>

and the corresponding execution of <a class="citerefentry" href="glEnd"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>.

</p><p>

<code class="constant">GL_INVALID_OPERATION</code> is generated if <a class="citerefentry" href="glEnd"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a> is executed without being

preceded by a <code class="function">glBegin</code>.

</p><p>

<code class="constant">GL_INVALID_OPERATION</code> is generated if a command other than

<a class="citerefentry" href="glVertex"><span class="citerefentry"><span class="refentrytitle">glVertex</span></span></a>,

<a class="citerefentry" href="glColor"><span class="citerefentry"><span class="refentrytitle">glColor</span></span></a>,

<a class="citerefentry" href="glSecondaryColor"><span class="citerefentry"><span class="refentrytitle">glSecondaryColor</span></span></a>,

<a class="citerefentry" href="glIndex"><span class="citerefentry"><span class="refentrytitle">glIndex</span></span></a>,

<a class="citerefentry" href="glNormal"><span class="citerefentry"><span class="refentrytitle">glNormal</span></span></a>,

<a class="citerefentry" href="glFogCoord"><span class="citerefentry"><span class="refentrytitle">glFogCoord</span></span></a>,

<a class="citerefentry" href="glTexCoord"><span class="citerefentry"><span class="refentrytitle">glTexCoord</span></span></a>,

<a class="citerefentry" href="glMultiTexCoord"><span class="citerefentry"><span class="refentrytitle">glMultiTexCoord</span></span></a>,

<a class="citerefentry" href="glVertexAttrib"><span class="citerefentry"><span class="refentrytitle">glVertexAttrib</span></span></a>,

<a class="citerefentry" href="glEvalCoord"><span class="citerefentry"><span class="refentrytitle">glEvalCoord</span></span></a>,

<a class="citerefentry" href="glEvalPoint"><span class="citerefentry"><span class="refentrytitle">glEvalPoint</span></span></a>,

<a class="citerefentry" href="glArrayElement"><span class="citerefentry"><span class="refentrytitle">glArrayElement</span></span></a>,

<a class="citerefentry" href="glMaterial"><span class="citerefentry"><span class="refentrytitle">glMaterial</span></span></a>,

<a class="citerefentry" href="glEdgeFlag"><span class="citerefentry"><span class="refentrytitle">glEdgeFlag</span></span></a>,

<a class="citerefentry" href="glCallList"><span class="citerefentry"><span class="refentrytitle">glCallList</span></span></a>, or

<a class="citerefentry" href="glCallLists"><span class="citerefentry"><span class="refentrytitle">glCallLists</span></span></a> is executed between

the execution of <code class="function">glBegin</code> and the corresponding

execution <a class="citerefentry" href="glEnd"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>.

</p><p>

Execution of

<a class="citerefentry" href="glEnableClientState"><span class="citerefentry"><span class="refentrytitle">glEnableClientState</span></span></a>,

<a class="citerefentry" href="glDisableClientState"><span class="citerefentry"><span class="refentrytitle">glDisableClientState</span></span></a>,

<a class="citerefentry" href="glEdgeFlagPointer"><span class="citerefentry"><span class="refentrytitle">glEdgeFlagPointer</span></span></a>,

<a class="citerefentry" href="glFogCoordPointer"><span class="citerefentry"><span class="refentrytitle">glFogCoordPointer</span></span></a>,

<a class="citerefentry" href="glTexCoordPointer"><span class="citerefentry"><span class="refentrytitle">glTexCoordPointer</span></span></a>,

<a class="citerefentry" href="glColorPointer"><span class="citerefentry"><span class="refentrytitle">glColorPointer</span></span></a>,

<a class="citerefentry" href="glSecondaryColorPointer"><span class="citerefentry"><span class="refentrytitle">glSecondaryColorPointer</span></span></a>,

<a class="citerefentry" href="glIndexPointer"><span class="citerefentry"><span class="refentrytitle">glIndexPointer</span></span></a>,

<a class="citerefentry" href="glNormalPointer"><span class="citerefentry"><span class="refentrytitle">glNormalPointer</span></span></a>,

<a class="citerefentry" href="glVertexPointer"><span class="citerefentry"><span class="refentrytitle">glVertexPointer</span></span></a>,

<a class="citerefentry" href="glVertexAttribPointer"><span class="citerefentry"><span class="refentrytitle">glVertexAttribPointer</span></span></a>,

<a class="citerefentry" href="glInterleavedArrays"><span class="citerefentry"><span class="refentrytitle">glInterleavedArrays</span></span></a>, or

<a class="citerefentry" href="glPixelStore"><span class="citerefentry"><span class="refentrytitle">glPixelStore</span></span></a> is not allowed after a call to <code class="function">glBegin</code> and before

the corresponding call to <a class="citerefentry" href="glEnd"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>,

but an error may or may not be generated.

</p></div>

{$pipelinestall}{$examples}

<div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>

<a class="citerefentry" href="glArrayElement"><span class="citerefentry"><span class="refentrytitle">glArrayElement</span></span></a>,

<a class="citerefentry" href="glCallList"><span class="citerefentry"><span class="refentrytitle">glCallList</span></span></a>,

<a class="citerefentry" href="glCallLists"><span class="citerefentry"><span class="refentrytitle">glCallLists</span></span></a>,

<a class="citerefentry" href="glColor"><span class="citerefentry"><span class="refentrytitle">glColor</span></span></a>,

<a class="citerefentry" href="glEdgeFlag"><span class="citerefentry"><span class="refentrytitle">glEdgeFlag</span></span></a>,

<a class="citerefentry" href="glEvalCoord"><span class="citerefentry"><span class="refentrytitle">glEvalCoord</span></span></a>,

<a class="citerefentry" href="glEvalPoint"><span class="citerefentry"><span class="refentrytitle">glEvalPoint</span></span></a>,

<a class="citerefentry" href="glFogCoord"><span class="citerefentry"><span class="refentrytitle">glFogCoord</span></span></a>,

<a class="citerefentry" href="glIndex"><span class="citerefentry"><span class="refentrytitle">glIndex</span></span></a>,

<a class="citerefentry" href="glMaterial"><span class="citerefentry"><span class="refentrytitle">glMaterial</span></span></a>,

<a class="citerefentry" href="glMultiTexCoord"><span class="citerefentry"><span class="refentrytitle">glMultiTexCoord</span></span></a>,

<a class="citerefentry" href="glNormal"><span class="citerefentry"><span class="refentrytitle">glNormal</span></span></a>,

<a class="citerefentry" href="glSecondaryColor"><span class="citerefentry"><span class="refentrytitle">glSecondaryColor</span></span></a>,

<a class="citerefentry" href="glTexCoord"><span class="citerefentry"><span class="refentrytitle">glTexCoord</span></span></a>,

<a class="citerefentry" href="glVertex"><span class="citerefentry"><span class="refentrytitle">glVertex</span></span></a>,

<a class="citerefentry" href="glVertexAttrib"><span class="citerefentry"><span class="refentrytitle">glVertexAttrib</span></span></a>

</p></div><div class="refsect1" lang="en" xml:lang="en"><div id="Copyright"><h2>Copyright</h2><p>

Copyright © 1991-2006

Silicon Graphics, Inc. This document is licensed under the SGI

Free Software B License. For details, see

<a class="ulink" href="https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/" target="_top">https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/</a>.

</p></div></div></div>