<div class="refentry" lang="en" xml:lang="en"><a id="glEvalMesh"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glEvalMesh — compute a one- or two-dimensional grid of points or lines</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table><tr><td><code class="funcdef">void <b class="fsfunc">glEvalMesh1</b>(</code></td><td>GLenum  </td><td><var class="pdparam">mode</var>, </td></tr><tr><td> </td><td>GLint  </td><td><var class="pdparam">i1</var>, </td></tr><tr><td> </td><td>GLint  </td><td><var class="pdparam">i2</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>

In <code class="function">glEvalMesh1</code>, specifies whether to compute a one-dimensional mesh of points or lines.

Symbolic constants

<code class="constant">GL_POINT</code> and

<code class="constant">GL_LINE</code> are accepted.

</p></dd><dt><span class="term"><em class="parameter"><code>i1</code></em>, </span><span class="term"><em class="parameter"><code>i2</code></em></span></dt><dd><p>

Specify the first and last integer values for grid domain variable

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

</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">glEvalMesh2</b>(</code></td><td>GLenum  </td><td><var class="pdparam">mode</var>, </td></tr><tr><td> </td><td>GLint  </td><td><var class="pdparam">i1</var>, </td></tr><tr><td> </td><td>GLint  </td><td><var class="pdparam">i2</var>, </td></tr><tr><td> </td><td>GLint  </td><td><var class="pdparam">j1</var>, </td></tr><tr><td> </td><td>GLint  </td><td><var class="pdparam">j2</var><code>)</code>;</td></tr></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="parameters2"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>mode</code></em></span></dt><dd><p>

In <code class="function">glEvalMesh2</code>, specifies whether to compute a two-dimensional mesh of points, lines,

or polygons.

Symbolic constants

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

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

<code class="constant">GL_FILL</code> are accepted.

</p></dd><dt><span class="term"><em class="parameter"><code>i1</code></em>, </span><span class="term"><em class="parameter"><code>i2</code></em></span></dt><dd><p>

Specify the first and last integer values for grid domain variable

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

</p></dd><dt><span class="term"><em class="parameter"><code>j1</code></em>, </span><span class="term"><em class="parameter"><code>j2</code></em></span></dt><dd><p>

Specify the first and last integer values for grid domain variable

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

</p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>

<a class="citerefentry" href="glMapGrid"><span class="citerefentry"><span class="refentrytitle">glMapGrid</span></span></a> and <code class="function">glEvalMesh</code> are used in tandem to efficiently

generate and evaluate a series of evenly-spaced map domain values.

<code class="function">glEvalMesh</code> steps through the integer domain of a one- or two-dimensional grid,

whose range is the domain of the evaluation maps specified by

<a class="citerefentry" href="glMap1"><span class="citerefentry"><span class="refentrytitle">glMap1</span></span></a> and <a class="citerefentry" href="glMap2"><span class="citerefentry"><span class="refentrytitle">glMap2</span></span></a>.

<em class="parameter"><code>mode</code></em> determines whether the resulting vertices are connected as

points,

lines,

or filled polygons.

</p><p>

In the one-dimensional case,

<code class="function">glEvalMesh1</code>,

the mesh is generated as if the following code fragment were executed:

</p><p>

</p><pre class="programlisting">

glBegin( <em class="parameter"><code>type</code></em> );

for ( i = <em class="parameter"><code>i1</code></em>; i &lt;= <em class="parameter"><code>i2</code></em>; i += 1 )

glEvalCoord1( <math overflow="scroll">

<mrow>

<mrow>

<mn>i</mn>

<mo>·</mo>

<mo>Δ</mo>

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

</mrow>

<mo>+</mo>

<msub>

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

<mn>1</mn>

</msub>

</mrow>

</math> );

glEnd();

</pre><p>

where

</p><p>

</p><div class="informalequation"><math overflow="scroll">

<mrow>

<mrow>

<mo>Δ</mo>

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

</mrow>

<mo>=</mo>

<mfrac>

<mfenced open="(" close=")">

<mrow>

<msub>

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

<mn>2</mn>

</msub>

<mo>-</mo>

<msub>

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

<mn>1</mn>

</msub>

</mrow>

</mfenced>

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

</mfrac>

</mrow>

</math></div><p>

</p><p>

and

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

<math overflow="scroll">

<msub><mi mathvariant="italic">u</mi>

<mn>1</mn>

</msub>

</math>,

and

<math overflow="scroll">

<msub><mi mathvariant="italic">u</mi>

<mn>2</mn>

</msub>

</math>

are the arguments to the most recent

<a class="citerefentry" href="glMapGrid1"><span class="citerefentry"><span class="refentrytitle">glMapGrid1</span></span></a> command.

<span class="emphasis"><em>type</em></span> is <code class="constant">GL_POINTS</code> if <em class="parameter"><code>mode</code></em> is <code class="constant">GL_POINT</code>,

or <code class="constant">GL_LINES</code> if <em class="parameter"><code>mode</code></em> is <code class="constant">GL_LINE</code>.

</p><p>

The one absolute numeric requirement is that if

<math overflow="scroll">

<mrow>

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

<mo>=</mo>

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

</mrow>

</math>,

then the

value computed from

<math overflow="scroll">

<mrow>

<mrow>

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

<mo>·</mo>

<mrow>

<mo>Δ</mo>

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

</mrow>

</mrow>

<mo>+</mo>

<msub><mi mathvariant="italic">u</mi>

<mn>1</mn>

</msub>

</mrow>

</math>

is exactly

<math overflow="scroll">

<msub><mi mathvariant="italic">u</mi>

<mn>2</mn>

</msub>

</math>.

</p><p>

In the two-dimensional case, <code class="function">glEvalMesh2</code>, let

.cp

</p><div class="informalequation"><math overflow="scroll">

<mrow>

<mrow>

<mo>Δ</mo>

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

</mrow>

<mo>=</mo>

<mfrac>

<mfenced open="(" close=")">

<mrow>

<msub><mi mathvariant="italic">u</mi>

<mn>2</mn>

</msub>

<mo>-</mo>

<msub><mi mathvariant="italic">u</mi>

<mn>1</mn>

</msub>

</mrow>

</mfenced>

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

</mfrac>

</mrow>

</math></div><p>

</p><p>

</p><div class="informalequation"><math overflow="scroll">

<mrow>

<mrow>

<mo>Δ</mo>

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

</mrow>

<mo>=</mo>

<mfrac>

<mfenced open="(" close=")">

<mrow>

<msub><mi mathvariant="italic">v</mi>

<mn>2</mn>

</msub>

<mo>-</mo>

<msub><mi mathvariant="italic">v</mi>

<mn>1</mn>

</msub>

</mrow>

</mfenced>

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

</mfrac>

</mrow>

</math></div><p>

</p><p>

where

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

<math overflow="scroll">

<msub><mi mathvariant="italic">u</mi>

<mn>1</mn>

</msub>

</math>,

<math overflow="scroll">

<msub><mi mathvariant="italic">u</mi>

<mn>2</mn>

</msub>

</math>,

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

<math overflow="scroll">

<msub><mi mathvariant="italic">v</mi>

<mn>1</mn>

</msub>

</math>,

and

<math overflow="scroll">

<msub><mi mathvariant="italic">v</mi>

<mn>2</mn>

</msub>

</math>

are the

arguments to the most recent <a class="citerefentry" href="glMapGrid2"><span class="citerefentry"><span class="refentrytitle">glMapGrid2</span></span></a> command. Then, if

<em class="parameter"><code>mode</code></em> is <code class="constant">GL_FILL</code>, the <code class="function">glEvalMesh2</code> command is equivalent

to:

</p><p>

</p><pre class="programlisting">

for ( j = <em class="parameter"><code>j1</code></em>; j &lt; <em class="parameter"><code>j2</code></em>; j += 1 ) {

glBegin( GL_QUAD_STRIP );

for ( i = <em class="parameter"><code>i1</code></em>; i &lt;= <em class="parameter"><code>i2</code></em>; i += 1 ) {

glEvalCoord2( <math overflow="scroll">

<mrow>

<mrow>

<mn>i</mn>

<mo>·</mo>

<mo>Δ</mo>

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

</mrow>

<mo>+</mo>

<msub>

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

<mn>1</mn>

</msub>

<mo>,</mo>

<mrow>

<mn>j</mn>

<mo>·</mo>

<mo>Δ</mo>

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

</mrow>

<mo>+</mo>

<msub>

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

<mn>1</mn>

</msub>

</mrow>

</math> );

glEvalCoord2( <math overflow="scroll">

<mrow>

<mrow>

<mn>i</mn>

<mo>·</mo>

<mo>Δ</mo>

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

</mrow>

<mo>+</mo>

<msub>

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

<mn>1</mn>

</msub>

<mo>,</mo>

<mrow>

<mrow>

<mfenced open="(" close=")">

<mrow>

<mn>j</mn>

<mo>+</mo>

<mn>1</mn>

</mrow>

</mfenced>

</mrow>

<mo>·</mo>

<mo>Δ</mo>

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

</mrow>

<mo>+</mo>

<msub>

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

<mn>1</mn>

</msub>

</mrow>

</math> );

}

glEnd();

}

</pre><p>

</p><p>

If <em class="parameter"><code>mode</code></em> is <code class="constant">GL_LINE</code>, then a call to <code class="function">glEvalMesh2</code> is equivalent to:

</p><p>

</p><pre class="programlisting">

for ( j = <em class="parameter"><code>j1</code></em>; j &lt;= <em class="parameter"><code>j2</code></em>; j += 1 ) {

glBegin( GL_LINE_STRIP );

for ( i = <em class="parameter"><code>i1</code></em>; i &lt;= <em class="parameter"><code>i2</code></em>; i += 1 )

glEvalCoord2( <math overflow="scroll">

<mrow>

<mrow>

<mn>i</mn>

<mo>·</mo>

<mo>Δ</mo>

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

</mrow>

<mo>+</mo>

<msub>

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

<mn>1</mn>

</msub>

<mo>,</mo>

<mrow>

<mn>j</mn>

<mo>·</mo>

<mo>Δ</mo>

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

</mrow>

<mo>+</mo>

<msub>

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

<mn>1</mn>

</msub>

</mrow>

</math> );

glEnd();

}

for ( i = <em class="parameter"><code>i1</code></em>; i &lt;= <em class="parameter"><code>i2</code></em>; i += 1 ) {

glBegin( GL_LINE_STRIP );

for ( j = <em class="parameter"><code>j1</code></em>; j &lt;= <em class="parameter"><code>j1</code></em>; j += 1 )

glEvalCoord2( <math overflow="scroll">

<mrow>

<mrow>

<mn>i</mn>

<mo>·</mo>

<mo>Δ</mo>

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

</mrow>

<mo>+</mo>

<msub>

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

<mn>1</mn>

</msub>

<mo>,</mo>

<mrow>

<mn>j</mn>

<mo>·</mo>

<mo>Δ</mo>

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

</mrow>

<mo>+</mo>

<msub>

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

<mn>1</mn>

</msub>

</mrow>

</math> );

glEnd();

}

</pre><p>

</p><p>

And finally, if <em class="parameter"><code>mode</code></em> is <code class="constant">GL_POINT</code>, then a call to

<code class="function">glEvalMesh2</code> is equivalent to:

</p><p>

</p><pre class="programlisting">

glBegin( GL_POINTS );

for ( j = <em class="parameter"><code>j1</code></em>; j &lt;= <em class="parameter"><code>j2</code></em>; j += 1 )

for ( i = <em class="parameter"><code>i1</code></em>; i &lt;= <em class="parameter"><code>i2</code></em>; i += 1 )

glEvalCoord2( <math overflow="scroll">

<mrow>

<mrow>

<mn>i</mn>

<mo>·</mo>

<mo>Δ</mo>

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

</mrow>

<mo>+</mo>

<msub>

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

<mn>1</mn>

</msub>

<mo>,</mo>

<mrow>

<mn>j</mn>

<mo>·</mo>

<mo>Δ</mo>

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

</mrow>

<mo>+</mo>

<msub>

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

<mn>1</mn>

</msub>

</mrow>

</math> );

glEnd();

</pre><p>

</p><p>

In all three cases, the only absolute numeric requirements are that if

<math overflow="scroll">

<mrow>

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

<mo>=</mo>

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

</mrow>

</math>,

then the value computed from

<math overflow="scroll">

<mrow>

<mrow>

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

<mo>·</mo>

<mrow>

<mo>Δ</mo>

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

</mrow>

</mrow>

<mo>+</mo>

<msub><mi mathvariant="italic">u</mi>

<mn>1</mn>

</msub>

</mrow>

</math>

is exactly

<math overflow="scroll">

<msub><mi mathvariant="italic">u</mi>

<mn>2</mn>

</msub>

</math>,

and if

<math overflow="scroll">

<mrow>

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

<mo>=</mo>

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

</mrow>

</math>,

then the value computed from

<math overflow="scroll">

<mrow>

<mrow>

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

<mo>·</mo>

<mrow>

<mo>Δ</mo>

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

</mrow>

</mrow>

<mo>+</mo>

<msub><mi mathvariant="italic">v</mi>

<mn>1</mn>

</msub>

</mrow>

</math>

is exactly

<math overflow="scroll">

<msub><mi mathvariant="italic">v</mi>

<mn>2</mn>

</msub>

</math>.

</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 not an accepted value.

</p><p>

<code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glEvalMesh</code>

is executed between the execution of <a class="citerefentry" href="glBegin"><span class="citerefentry"><span class="refentrytitle">glBegin</span></span></a>

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

</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p>

<a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_MAP1_GRID_DOMAIN</code>

</p><p>

<a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_MAP2_GRID_DOMAIN</code>

</p><p>

<a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_MAP1_GRID_SEGMENTS</code>

</p><p>

<a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_MAP2_GRID_SEGMENTS</code>

</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="glBegin"><span class="citerefentry"><span class="refentrytitle">glBegin</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="glMap1"><span class="citerefentry"><span class="refentrytitle">glMap1</span></span></a>,

<a class="citerefentry" href="glMap2"><span class="citerefentry"><span class="refentrytitle">glMap2</span></span></a>,

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