<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd"><!-- saved from url=(0013)about:internet -->
<?xml-stylesheet type="text/xsl" href="mathml.xsl"?><html xmlns="http://www.w3.org/1999/xhtml" xmlns:pref="http://www.w3.org/2002/Math/preference" pref:renderer="mathplayer-dl"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>glEvalPoint</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1" /></head><body><div class="refentry"><a id="glEvalPoint"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glEvalPoint — generate and evaluate a single point in a mesh</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void <strong class="fsfunc">glEvalPoint1</strong>(</code></td><td>GLint <var class="pdparam">i</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div><div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void <strong class="fsfunc">glEvalPoint2</strong>(</code></td><td>GLint <var class="pdparam">i</var>, </td></tr><tr><td> </td><td>GLint <var class="pdparam">j</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>i</code></em></span></dt><dd><p>
                    Specifies the integer value for grid domain variable 
                    <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">i</mml:mi></mml:math>.
                </p></dd><dt><span class="term"><em class="parameter"><code>j</code></em></span></dt><dd><p>
                    Specifies the integer value for grid domain variable 
                    <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">j</mml:mi></mml:math>
                    (<code class="function">glEvalPoint2</code> only).
                </p></dd></dl></div></div><div class="refsect1"><a id="description"></a><h2>Description</h2><p>
            <a class="citerefentry" href="glMapGrid.xml"><span class="citerefentry"><span class="refentrytitle">glMapGrid</span></span></a> and <a class="citerefentry" href="glEvalMesh.xml"><span class="citerefentry"><span class="refentrytitle">glEvalMesh</span></span></a> are used in tandem to efficiently
            generate and evaluate a series of evenly spaced map domain values.
            <code class="function">glEvalPoint</code> can be used to evaluate a single grid point in the same gridspace
            that is traversed by <a class="citerefentry" href="glEvalMesh.xml"><span class="citerefentry"><span class="refentrytitle">glEvalMesh</span></span></a>.
            Calling <code class="function">glEvalPoint1</code> is equivalent to calling
            </p><pre class="programlisting">
glEvalCoord1( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
	          
     	          <mml:mrow>
     	              <mml:mrow>
     	                  <mml:mn>i</mml:mn>
     	                  <mml:mo>·</mml:mo>
     	                  <mml:mo>Δ</mml:mo>
     	                  <mml:mi mathvariant="italic">u</mml:mi>
     	              </mml:mrow>
     	              <mml:mo>+</mml:mo>
     	              <mml:msub>
     	                  <mml:mi mathvariant="italic">u</mml:mi>
     	                  <mml:mn>1</mml:mn>
     	              </mml:msub>
     	          </mml:mrow>
              </mml:math> );
         </pre><p>
            where
            </p><div class="informalequation"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:mrow>
                    <mml:mrow>
                        <mml:mo>Δ</mml:mo>
                        <mml:mi mathvariant="italic">u</mml:mi>
                    </mml:mrow>
                    <mml:mo>=</mml:mo>
                    <mml:mfrac>
                        <mml:mfenced open="(" close=")">
                            <mml:mrow>
                                <mml:msub><mml:mi mathvariant="italic">u</mml:mi>
                                <mml:mn>2</mml:mn>
                                </mml:msub>
                                <mml:mo>-</mml:mo>
                                <mml:msub><mml:mi mathvariant="italic">u</mml:mi>
                                <mml:mn>1</mml:mn>
                                </mml:msub>
                            </mml:mrow>
                        </mml:mfenced>
                        <mml:mi mathvariant="italic">n</mml:mi>
                    </mml:mfrac>
                </mml:mrow>
            </mml:math></div><p>
        </p><p>
            and 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">n</mml:mi></mml:math>, 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:msub><mml:mi mathvariant="italic">u</mml:mi>
                <mml:mn>1</mml:mn>
                </mml:msub>
            </mml:math>,
            and 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:msub><mml:mi mathvariant="italic">u</mml:mi>
                <mml:mn>2</mml:mn>
                </mml:msub>
            </mml:math>
            are the arguments to the most recent <a class="citerefentry" href="glMapGrid1.xml"><span class="citerefentry"><span class="refentrytitle">glMapGrid1</span></span></a> command.
            The one absolute numeric requirement is that if 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:mrow>
                    <mml:mi mathvariant="italic">i</mml:mi>
                    <mml:mo>=</mml:mo>
                    <mml:mi mathvariant="italic">n</mml:mi>
                </mml:mrow>
            </mml:math>,
            then the value computed from
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:mrow>
                    <mml:mrow>
                        <mml:mi mathvariant="italic">i</mml:mi>
                        <mml:mo>·</mml:mo>
                        <mml:mrow>
                            <mml:mo>Δ</mml:mo>
                            <mml:mi mathvariant="italic">u</mml:mi>
                        </mml:mrow>
                    </mml:mrow>
                    <mml:mo>+</mml:mo>
                    <mml:msub><mml:mi mathvariant="italic">u</mml:mi>
                    <mml:mn>1</mml:mn>
                    </mml:msub>
                </mml:mrow>
            </mml:math>
            is exactly 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:msub><mml:mi mathvariant="italic">u</mml:mi>
                <mml:mn>2</mml:mn>
                </mml:msub>
            </mml:math>.
        </p><p>
            In the two-dimensional case, <code class="function">glEvalPoint2</code>, let
        </p><p>
            </p><div class="informalequation"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:mrow>
                    <mml:mrow>
                        <mml:mo>Δ</mml:mo>
                        <mml:mi mathvariant="italic">u</mml:mi>
                    </mml:mrow>
                    <mml:mo>=</mml:mo>
                    <mml:mfrac>
                        <mml:mfenced open="(" close=")">
                            <mml:mrow>
                                <mml:msub><mml:mi mathvariant="italic">u</mml:mi>
                                <mml:mn>2</mml:mn>
                                </mml:msub>
                                <mml:mo>-</mml:mo>
                                <mml:msub><mml:mi mathvariant="italic">u</mml:mi>
                                <mml:mn>1</mml:mn>
                                </mml:msub>
                            </mml:mrow>
                        </mml:mfenced>
                        <mml:mi mathvariant="italic">n</mml:mi>
                    </mml:mfrac>
                </mml:mrow>
            </mml:math></div><p>
            </p><p>
                </p><div class="informalequation"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                    
                    <mml:mrow>
                        <mml:mrow>
                            <mml:mo>Δ</mml:mo>
                            <mml:mi mathvariant="italic">v</mml:mi>
                        </mml:mrow>
                        <mml:mo>=</mml:mo>
                        <mml:mfrac>
                            <mml:mfenced open="(" close=")">
                                <mml:mrow>
                                    <mml:msub><mml:mi mathvariant="italic">v</mml:mi>
                                    <mml:mn>2</mml:mn>
                                    </mml:msub>
                                    <mml:mo>-</mml:mo>
                                    <mml:msub><mml:mi mathvariant="italic">v</mml:mi>
                                    <mml:mn>1</mml:mn>
                                    </mml:msub>
                                </mml:mrow>
                            </mml:mfenced>
                            <mml:mi mathvariant="italic">m</mml:mi>
                        </mml:mfrac>
                    </mml:mrow>
                </mml:math></div><p>
            </p><p>
        </p><p>
            where 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">n</mml:mi></mml:math>, 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:msub><mml:mi mathvariant="italic">u</mml:mi>
                <mml:mn>1</mml:mn>
                </mml:msub>
            </mml:math>, 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:msub><mml:mi mathvariant="italic">u</mml:mi>
                <mml:mn>2</mml:mn>
                </mml:msub>
            </mml:math>, 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">m</mml:mi></mml:math>, 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:msub><mml:mi mathvariant="italic">v</mml:mi>
                <mml:mn>1</mml:mn>
                </mml:msub>
            </mml:math>,
            and 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:msub><mml:mi mathvariant="italic">v</mml:mi>
                <mml:mn>2</mml:mn>
                </mml:msub>
            </mml:math>
            are the arguments to the most recent <a class="citerefentry" href="glMapGrid2.xml"><span class="citerefentry"><span class="refentrytitle">glMapGrid2</span></span></a> command.
            Then the <code class="function">glEvalPoint2</code> command is equivalent to calling
            </p><pre class="programlisting">
glEvalCoord2( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
			
		        <mml:mrow>
			    <mml:mrow>
			        <mml:mn>i</mml:mn>
				<mml:mo>·</mml:mo>
			        <mml:mo>Δ</mml:mo>
		                <mml:mi mathvariant="italic">u</mml:mi>
			    </mml:mrow>
		            <mml:mo>+</mml:mo>
		            <mml:msub>
		                <mml:mi mathvariant="italic">u</mml:mi>
		                <mml:mn>1</mml:mn>
		            </mml:msub>
			    <mml:mo>,</mml:mo>
			    
			    <mml:mrow>
			        <mml:mn>j</mml:mn>
				<mml:mo>·</mml:mo>
			        <mml:mo>Δ</mml:mo>
		                <mml:mi mathvariant="italic">v</mml:mi>

			    </mml:mrow>
		            <mml:mo>+</mml:mo>
		            <mml:msub>
		                <mml:mi mathvariant="italic">v</mml:mi>
		                <mml:mn>1</mml:mn>
		            </mml:msub>
			</mml:mrow>
		    </mml:math> );
            </pre><p>
            The only absolute numeric requirements are that if 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:mrow>
                    <mml:mi mathvariant="italic">i</mml:mi>
                    <mml:mo>=</mml:mo>
                    <mml:mi mathvariant="italic">n</mml:mi>
                </mml:mrow>
            </mml:math>,
            then the value computed from
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:mrow>
                    <mml:mrow>
                        <mml:mi mathvariant="italic">i</mml:mi>
                        <mml:mo>·</mml:mo>
                        <mml:mrow>
                            <mml:mo>Δ</mml:mo>
                            <mml:mi mathvariant="italic">u</mml:mi>
                        </mml:mrow>
                    </mml:mrow>
                    <mml:mo>+</mml:mo>
                    <mml:msub><mml:mi mathvariant="italic">u</mml:mi>
                    <mml:mn>1</mml:mn>
                    </mml:msub>
                </mml:mrow>
            </mml:math>
            is exactly 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:msub><mml:mi mathvariant="italic">u</mml:mi>
                <mml:mn>2</mml:mn>
                </mml:msub>
            </mml:math>,
            and if 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:mrow>
                    <mml:mi mathvariant="italic">j</mml:mi>
                    <mml:mo>=</mml:mo>
                    <mml:mi mathvariant="italic">m</mml:mi>
                </mml:mrow>
            </mml:math>,
            then the value computed from
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:mrow>
                    <mml:mrow>
                        <mml:mi mathvariant="italic">j</mml:mi>
                        <mml:mo>·</mml:mo>
                        <mml:mrow>
                            <mml:mo>Δ</mml:mo>
                            <mml:mi mathvariant="italic">v</mml:mi>
                        </mml:mrow>
                    </mml:mrow>
                    <mml:mo>+</mml:mo>
                    <mml:msub><mml:mi mathvariant="italic">v</mml:mi>
                    <mml:mn>1</mml:mn>
                    </mml:msub>
                </mml:mrow>
            </mml:math>
            is exactly 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:msub><mml:mi mathvariant="italic">v</mml:mi>
                <mml:mn>2</mml:mn>
                </mml:msub>
            </mml:math>.
        </p></div><div class="refsect1"><a id="associatedgets"></a><h2>Associated Gets</h2><p>
            <a class="citerefentry" href="glGet.xml"><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.xml"><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.xml"><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.xml"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_MAP2_GRID_SEGMENTS</code>
        </p></div><div class="refsect1"><a id="seealso"></a><h2>See Also</h2><p>
            <a class="citerefentry" href="glEvalCoord.xml"><span class="citerefentry"><span class="refentrytitle">glEvalCoord</span></span></a>,
            <a class="citerefentry" href="glEvalMesh.xml"><span class="citerefentry"><span class="refentrytitle">glEvalMesh</span></span></a>,
            <a class="citerefentry" href="glMap1.xml"><span class="citerefentry"><span class="refentrytitle">glMap1</span></span></a>,
            <a class="citerefentry" href="glMap2.xml"><span class="citerefentry"><span class="refentrytitle">glMap2</span></span></a>,
            <a class="citerefentry" href="glMapGrid.xml"><span class="citerefentry"><span class="refentrytitle">glMapGrid</span></span></a>
        </p></div><div class="refsect1"><a id="Copyright"></a><h2>Copyright</h2><p>
            Copyright <span class="trademark"></span>© 1991-2006
            Silicon Graphics, Inc. This document is licensed under the SGI
            Free Software B License. For details, see
            <a class="ulink" href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>.
        </p></div></div></body></html>