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glEvalMesh.xhtml
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glEvalMesh.xhtml
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<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 <= <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 < <em class="parameter"><code>j2</code></em>; j += 1 ) {
glBegin( GL_QUAD_STRIP );
for ( i = <em class="parameter"><code>i1</code></em>; i <= <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 <= <em class="parameter"><code>j2</code></em>; j += 1 ) {
glBegin( GL_LINE_STRIP );
for ( i = <em class="parameter"><code>i1</code></em>; i <= <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 <= <em class="parameter"><code>i2</code></em>; i += 1 ) {
glBegin( GL_LINE_STRIP );
for ( j = <em class="parameter"><code>j1</code></em>; j <= <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 <= <em class="parameter"><code>j2</code></em>; j += 1 )
for ( i = <em class="parameter"><code>i1</code></em>; i <= <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>