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><head><title>glEvalPoint</title><link rel="stylesheet" href="style.css" type="text/css"/><meta name="generator" content="DocBook XSL Stylesheets V1.59.1"/><link rel="home" href="index.xml" title="PyOpenGL 2.0.1.07 Man Pages"/><link rel="up" href="reference-GL.xml" title="GL"/><link rel="previous" href="glEvalMesh.3G.xml" title="glEvalMesh"/><link rel="next" href="glFeedbackBuffer.3G.xml" title="glFeedbackBuffer"/></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">glEvalPoint</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="glEvalMesh.3G.xml">Prev</a> </td><th width="60%" align="center">GL</th><td width="20%" align="right"> <a accesskey="n" href="glFeedbackBuffer.3G.xml">Next</a></td></tr></table><hr/></div><div class="refentry" lang="en"><a name="glEvalPoint.3G"/><div class="titlepage"/><div class="refnamediv"><a name="glEvalPoint.3G-name"/><h2>Name</h2><p>glEvalPoint1, glEvalPoint2 &#8212; generate and evaluate a single point in a mesh</p></div><div class="refsynopsisdiv"><a name="glEvalPoint.3G-c_spec"/><h2>C Specification</h2><table class="funcprototype" border="0" cellpadding="0" cellspacing="0"><tr><td valign="top"><code>void <tt>glEvalPoint1</tt></code></td><td valign="top"><code>(</code></td><td valign="top"><code>GLint <i><tt>i</tt></i>);</code></td></tr><tr><td valign="top"><code>void <tt>glEvalPoint2</tt></code></td><td valign="top"><code>(</code></td><td valign="top"><code>GLint <i><tt>i</tt></i>, GLint <i><tt>j</tt></i>);</code></td></tr></table></div><div class="refsynopsisdiv"><a name="glEvalPoint.3G-python_spec"/><h2>Python Specification</h2><table class="funcprototype" border="0" cellpadding="0" cellspacing="0"><tr><td valign="top"><code><tt>glEvalPoint1</tt></code></td><td valign="top"><code>(</code></td><td valign="top"><code><i><tt>i</tt></i>) &#8594; <tt>None</tt></code></td></tr><tr><td valign="top"><code><tt>glEvalPoint2</tt></code></td><td valign="top"><code>(</code></td><td valign="top"><code><i><tt>i</tt></i>, <i><tt>j</tt></i>) &#8594; <tt>None</tt></code></td></tr></table></div><div class="refsect1" lang="en"><a name="glEvalPoint.3G-parameters"/><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><i><tt>i</tt></i></span></dt><dd>
						Specifies the integer value for grid domain variable <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
								<mml:mi>i</mml:mi>
							</mml:math>.
					</dd><dt><span class="term"><i><tt>j</tt></i></span></dt><dd>
						Specifies the integer value for grid domain variable <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
								<mml:mi>j</mml:mi>
							</mml:math> (<tt>glEvalPoint2</tt> only).
					</dd></dl></div></div><div class="refsect1" lang="en"><a name="glEvalPoint.3G-description"/><h2>Description</h2><p>
			<tt>glMapGrid</tt> and <tt>glEvalMesh</tt> are used in
			tandem to efficiently generate and evaluate a series of evenly spaced map domain values. <tt>glEvalPoint</tt> can be used to evaluate a single grid point in the same gridspace that is
			traversed by <tt>glEvalMesh</tt>. Calling <tt>glEvalPoint1</tt> is
			equivalent to calling
		</p><p>
			glEvalCoord1( i<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
					<mml:mrow>
						<mml:mo>·</mml:mo>
						<mml:mi>&#916;</mml:mi>
						<mml:mi>u</mml:mi>
						<mml:mo>+</mml:mo>
						<mml:msub>
							<mml:mi>u</mml:mi>
							<mml:mn>1</mml:mn>
						</mml:msub>
					</mml:mrow>
				</mml:math> );
		</p><p>
			where <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
					<mml:mrow>
						<mml:mi>&#916;</mml:mi>
						<mml:mi>u</mml:mi>
						<mml:mo>=</mml:mo>
						<mml:mo>(</mml:mo>
						<mml:msub>
							<mml:mi>u</mml:mi>
							<mml:mn>2</mml:mn>
						</mml:msub>
						<mml:mo>-</mml:mo>
						<mml:msub>
							<mml:mi>u</mml:mi>
							<mml:mn>1</mml:mn>
						</mml:msub>
						<mml:mo>)</mml:mo>
						<mml:mo>/</mml:mo>
						<mml:mi>n</mml:mi>
					</mml:mrow>
				</mml:math>
		</p><p>
			and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
					<mml:mi>n</mml:mi>
				</mml:math>, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
					<mml:msub>
						<mml:mi>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>u</mml:mi>
						<mml:mn>2</mml:mn>
					</mml:msub>
				</mml:math> are the arguments to the most recent <tt>glMapGrid1</tt> 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>i</mml:mi>
						<mml:mo>=</mml:mo>
						<mml:mi>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:mi>i</mml:mi>
						<mml:mo>·</mml:mo>
						<mml:mi>&#916;</mml:mi>
						<mml:mi>u</mml:mi>
						<mml:mo>+</mml:mo>
						<mml:msub>
							<mml:mi>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>u</mml:mi>
						<mml:mn>2</mml:mn>
					</mml:msub>
				</mml:math>.
		</p><p>
			In the two-dimensional case, <tt>glEvalPoint2</tt>, let
		</p><p>
			<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
					<mml:mrow>
						<mml:mi>&#916;</mml:mi>
						<mml:mi>u</mml:mi>
						<mml:mo>=</mml:mo>
						<mml:mo>(</mml:mo>
						<mml:msub>
							<mml:mi>u</mml:mi>
							<mml:mn>2</mml:mn>
						</mml:msub>
						<mml:mo>-</mml:mo>
						<mml:msub>
							<mml:mi>u</mml:mi>
							<mml:mn>1</mml:mn>
						</mml:msub>
						<mml:mo>)</mml:mo>
						<mml:mo>/</mml:mo>
						<mml:mi>n</mml:mi>
					</mml:mrow>
				</mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
					<mml:mrow>
						<mml:mi>&#916;</mml:mi>
						<mml:mi>v</mml:mi>
						<mml:mo>=</mml:mo>
						<mml:mo>(</mml:mo>
						<mml:msub>
							<mml:mi>v</mml:mi>
							<mml:mn>2</mml:mn>
						</mml:msub>
						<mml:mo>-</mml:mo>
						<mml:msub>
							<mml:mi>v</mml:mi>
							<mml:mn>1</mml:mn>
						</mml:msub>
						<mml:mo>)</mml:mo>
						<mml:mo>/</mml:mo>
						<mml:mi>m</mml:mi>
					</mml:mrow>
				</mml:math>
		</p><p>
			where <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
					<mml:mi>n</mml:mi>
				</mml:math>, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
					<mml:msub>
						<mml:mi>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>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>m</mml:mi>
				</mml:math>, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
					<mml:msub>
						<mml:mi>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>v</mml:mi>
						<mml:mn>2</mml:mn>
					</mml:msub>
				</mml:math> are the arguments to the most recent <tt>glMapGrid2</tt> command.
			Then the <tt>glEvalPoint2</tt> command is equivalent to calling
		</p><p>
			glEvalCoord2( i<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
					<mml:mrow>
						<mml:mo>·</mml:mo>
						<mml:mi>&#916;</mml:mi>
						<mml:mi>u</mml:mi>
						<mml:mo>+</mml:mo>
						<mml:msub>
							<mml:mi>u</mml:mi>
							<mml:mn>1</mml:mn>
						</mml:msub>
					</mml:mrow>
				</mml:math>, j<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
					<mml:mrow>
						<mml:mo>·</mml:mo>
						<mml:mi>&#916;</mml:mi>
						<mml:mi>v</mml:mi>
						<mml:mo>+</mml:mo>
						<mml:msub>
							<mml:mi>v</mml:mi>
							<mml:mn>1</mml:mn>
						</mml:msub>
					</mml:mrow>
				</mml:math> );
		</p><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>i</mml:mi>
						<mml:mo>=</mml:mo>
						<mml:mi>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:mi>i</mml:mi>
						<mml:mo>·</mml:mo>
						<mml:mi>&#916;</mml:mi>
						<mml:mi>u</mml:mi>
						<mml:mo>+</mml:mo>
						<mml:msub>
							<mml:mi>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>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>j</mml:mi>
						<mml:mo>=</mml:mo>
						<mml:mi>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:mi>i</mml:mi>
						<mml:mo>·</mml:mo>
						<mml:mi>&#916;</mml:mi>
						<mml:mi>v</mml:mi>
						<mml:mo>+</mml:mo>
						<mml:msub>
							<mml:mi>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>v</mml:mi>
						<mml:mn>2</mml:mn>
					</mml:msub>
				</mml:math>.
		</p></div><div class="refsect1" lang="en"><a name="glEvalPoint.3G-associated_gets"/><h2>Associated Gets</h2><p>
			<tt>glGet</tt> with argument <tt>GL_MAP1_GRID_DOMAIN</tt>
		</p><p>
			<tt>glGet</tt> with argument <tt>GL_MAP2_GRID_DOMAIN</tt>
		</p><p>
			<tt>glGet</tt> with argument <tt>GL_MAP1_GRID_SEGMENTS</tt>
		</p><p>
			<tt>glGet</tt> with argument <tt>GL_MAP2_GRID_SEGMENTS</tt>
		</p></div><div class="refsect1" lang="en"><a name="glEvalPoint.3G-see_also"/><h2>See Also</h2><p>
			<span class="simplelist"><a href="glEvalCoord.3G.xml">glEvalCoord</a>, <a href="glEvalMesh.3G.xml">glEvalMesh</a>, <a href="glMap1.3G.xml">glMap1</a>, <a href="glMap2.3G.xml">glMap2</a>, <a href="glMapGrid.3G.xml">glMapGrid</a></span>
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