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<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE html
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<html
xmlns="http://www.w3.org/1999/xhtml"
xmlns:mml="http://www.w3.org/1998/Math/MathML"
><head><title>glFrustum</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="glFrontFace.3G.xml" title="glFrontFace"/><link rel="next" href="glGenLists.3G.xml" title="glGenLists"/></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">glFrustum</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="glFrontFace.3G.xml">Prev</a></td><th width="60%" align="center">GL</th><td width="20%" align="right"><a accesskey="n" href="glGenLists.3G.xml">Next</a></td></tr></table><hr/></div><div class="refentry" lang="en"><a name="glFrustum.3G"/><div class="titlepage"/><div class="refnamediv"><a name="glFrustum.3G-name"/><h2>Name</h2><p>glFrustum — multiply the current matrix by a perspective matrix</p></div><div class="refsynopsisdiv"><a name="glFrustum.3G-c_spec"/><h2>C Specification</h2><table class="funcprototype" border="0" cellpadding="0" cellspacing="0"><tr><td valign="top"><code>void<tt>glFrustum</tt></code></td><td valign="top"><code>(</code></td><td valign="top"><code>GLdouble<i><tt>left</tt></i>, GLdouble<i><tt>right</tt></i>, GLdouble<i><tt>bottom</tt></i>, GLdouble<i><tt>top</tt></i>, GLdouble<i><tt>zNear</tt></i>, GLdouble<i><tt>zFar</tt></i>);</code></td></tr></table></div><div class="refsynopsisdiv"><a name="glFrustum.3G-python_spec"/><h2>Python Specification</h2><table class="funcprototype" border="0" cellpadding="0" cellspacing="0"><tr><td valign="top"><code><tt>glFrustum</tt></code></td><td valign="top"><code>(</code></td><td valign="top"><code><i><tt>left</tt></i>, <i><tt>right</tt></i>, <i><tt>bottom</tt></i>, <i><tt>top</tt></i>, <i><tt>zNear</tt></i>, <i><tt>zFar</tt></i>) →<tt>None</tt></code></td></tr></table></div><div class="refsect1" lang="en"><a name="glFrustum.3G-parameters"/><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><i><tt>left</tt></i>, <i><tt>right</tt></i></span></dt><dd>
Specify the coordinates for the left and right vertical clipping planes.
</dd><dt><span class="term"><i><tt>bottom</tt></i>, <i><tt>top</tt></i></span></dt><dd>
Specify the coordinates for the bottom and top horizontal clipping planes.
</dd><dt><span class="term"><i><tt>zNear</tt></i>, <i><tt>zFar</tt></i></span></dt><dd>
Specify the distances to the near and far depth clipping planes. Both distances must be positive.
</dd></dl></div></div><div class="refsect1" lang="en"><a name="glFrustum.3G-description"/><h2>Description</h2><p>
<tt>glFrustum</tt> describes a perspective matrix that produces a perspective projection. The current
matrix (see <a href="glMatrixMode.3G.xml">glMatrixMode</a>) is multiplied by this matrix and the result replaces the current matrix, as if <tt>glMultMatrix</tt> were called with the following matrix as its argument:
</p><p>
</p><div class="informalequation"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" mode="display" overflow="scroll">
<mml:mrow>
<mml:mo>[</mml:mo>
<mml:mtable>
<mml:mtr>
<mml:mtd columnalign="center">
<mml:mfrac>
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:mi>zNear</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>right</mml:mi>
<mml:mo>-</mml:mo>
<mml:mi>left</mml:mi>
</mml:mrow>
</mml:mfrac>
</mml:mtd>
<mml:mtd columnalign="center">
<mml:mn>0</mml:mn>
</mml:mtd>
<mml:mtd columnalign="center">
<mml:mi>A</mml:mi>
</mml:mtd>
<mml:mtd columnalign="center">
<mml:mn>0</mml:mn>
</mml:mtd>
</mml:mtr>
<mml:mtr>
<mml:mtd columnalign="center">
<mml:mn>0</mml:mn>
</mml:mtd>
<mml:mtd columnalign="center">
<mml:mfrac>
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:mi>zNear</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>top</mml:mi>
<mml:mo>-</mml:mo>
<mml:mi>bottom</mml:mi>
</mml:mrow>
</mml:mfrac>
</mml:mtd>
<mml:mtd columnalign="center">
<mml:mi>B</mml:mi>
</mml:mtd>
<mml:mtd columnalign="center">
<mml:mn>0</mml:mn>
</mml:mtd>
</mml:mtr>
<mml:mtr>
<mml:mtd columnalign="center">
<mml:mn>0</mml:mn>
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<mml:mtd columnalign="center">
<mml:mn>0</mml:mn>
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<mml:mtd columnalign="center">
<mml:mi>C</mml:mi>
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<mml:mtd columnalign="center">
<mml:mi>D</mml:mi>
</mml:mtd>
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<mml:mtr>
<mml:mtd columnalign="center">
<mml:mn>0</mml:mn>
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<mml:mtd columnalign="center">
<mml:mn>0</mml:mn>
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<mml:mtd columnalign="center">
<mml:mn>-1</mml:mn>
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<mml:mtd columnalign="center">
<mml:mn>0</mml:mn>
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<mml:mo>]</mml:mo>
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<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mo>=</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>right</mml:mi>
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<mml:mi>left</mml:mi>
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<mml:mrow>
<mml:mi>right</mml:mi>
<mml:mo>-</mml:mo>
<mml:mi>left</mml:mi>
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</mml:mfrac>
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<mml:mrow>
<mml:mi>B</mml:mi>
<mml:mo>=</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>top</mml:mi>
<mml:mo>+</mml:mo>
<mml:mi>bottom</mml:mi>
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<mml:mrow>
<mml:mi>top</mml:mi>
<mml:mo>-</mml:mo>
<mml:mi>bottom</mml:mi>
</mml:mrow>
</mml:mfrac>
</mml:mrow>
</mml:math></div><div class="informalequation"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" mode="display" overflow="scroll">
<mml:mrow>
<mml:mi>C</mml:mi>
<mml:mo>=</mml:mo>
<mml:mo>-</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>zFar</mml:mi>
<mml:mo>+</mml:mo>
<mml:mi>zNear</mml:mi>
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<mml:mrow>
<mml:mi>zFar</mml:mi>
<mml:mo>-</mml:mo>
<mml:mi>zNear</mml:mi>
</mml:mrow>
</mml:mfrac>
</mml:mrow>
</mml:math></div><div class="informalequation"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" mode="display" overflow="scroll">
<mml:mrow>
<mml:mi>D</mml:mi>
<mml:mo>=</mml:mo>
<mml:mo>-</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:mi>zFar</mml:mi>
<mml:mi>zNear</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>zFar</mml:mi>
<mml:mo>-</mml:mo>
<mml:mi>zNear</mml:mi>
</mml:mrow>
</mml:mfrac>
</mml:mrow>
</mml:math></div><p>
</p><p>
Typically, the matrix mode is <tt>GL_PROJECTION</tt>, and (<i><tt>left</tt></i>,
<i><tt>bottom</tt></i>, -<i><tt>zNear</tt></i>) and (<i><tt>right</tt></i>,
<i><tt>top</tt></i>, -<i><tt>zNear</tt></i>) specify the points on the near clipping plane that are
mapped to the lower left and upper right corners of the window, assuming that the eye is located at (0, 0, 0).
-<i><tt>zFar</tt></i> specifies the location of the far clipping plane. Both <i><tt>zNear</tt></i> and
<i><tt>zFar</tt></i> must be positive.
</p><p>
Use <a href="glPushMatrix.3G.xml"><tt>glPushMatrix</tt></a> and <a href="glPushMatrix.3G.xml"><tt>glPopMatrix</tt></a> to
save and restore the current matrix stack.
</p></div><div class="refsect1" lang="en"><a name="glFrustum.3G-notes"/><h2>Notes</h2><p>
Depth buffer precision is affected by the values specified for <i><tt>zNear</tt></i> and
<i><tt>zFar</tt></i>. The greater the ratio of <i><tt>zFar</tt></i> to <i><tt>zNear</tt></i> is,
the less effective the depth buffer will be at distinguishing between surfaces that are near each other. If
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mrow>
<mml:mi>r</mml:mi>
<mml:mo>=</mml:mo>
<mml:mfrac>
<mml:mi>zFar</mml:mi>
<mml:mi>zNear</mml:mi>
</mml:mfrac>
</mml:mrow>
</mml:math> roughly <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mrow>
<mml:msub>
<mml:mi>log</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
<mml:mo>(</mml:mo>
<mml:mi>r</mml:mi>
<mml:mo>)</mml:mo>
</mml:mrow>
</mml:math> bits of depth buffer precision are lost. Because <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mi>r</mml:mi>
</mml:math> approaches infinity as <i><tt>zNear</tt></i> approaches 0, <i><tt>zNear</tt></i> must
never be set to 0.
</p></div><div class="refsect1" lang="en"><a name="glFrustum.3G-errors"/><h2>Errors</h2><p>
<tt>GL_INVALID_VALUE</tt> is generated if <i><tt>zNear</tt></i> or <i><tt>zFar</tt></i> is
not positive, or if <i><tt>left</tt></i> = <i><tt>right</tt></i>, or <i><tt>bottom</tt></i> =
<i><tt>top</tt></i>.
</p><p>
<tt>GL_INVALID_OPERATION</tt> is generated if <tt>glFrustum</tt> is executed between the
execution of <a href="glBegin.3G.xml"><tt>glBegin</tt></a> and the corresponding execution of <a href="glBegin.3G.xml"><tt>glEnd</tt></a>.
</p></div><div class="refsect1" lang="en"><a name="glFrustum.3G-associated_gets"/><h2>Associated Gets</h2><p>
<tt>glGet</tt> with argument <tt>GL_MATRIX_MODE</tt>
</p><p>
<tt>glGet</tt> with argument <tt>GL_MODELVIEW_MATRIX</tt>
</p><p>
<tt>glGet</tt> with argument <tt>GL_PROJECTION_MATRIX</tt>
</p><p>
<tt>glGet</tt> with argument <tt>GL_TEXTURE_MATRIX</tt>
</p><p>
<tt>glGet</tt> with argument <tt>GL_COLOR_MATRIX</tt>
</p></div><div class="refsect1" lang="en"><a name="glFrustum.3G-see_also"/><h2>See Also</h2><p>
<span class="simplelist"><a href="glOrtho.3G.xml">glOrtho</a>, <a href="glMatrixMode.3G.xml">glMatrixMode</a>, <a href="glMultMatrix.3G.xml">glMultMatrix</a>, <a href="glPushMatrix.3G.xml">glPushMatrix</a>, <a href="glViewport.3G.xml">glViewport</a></span>
</p></div></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="glFrontFace.3G.xml">Prev</a></td><td width="20%" align="center"><a accesskey="u" href="reference-GL.xml">Up</a></td><td width="40%" align="right"><a accesskey="n" href="glGenLists.3G.xml">Next</a></td></tr><tr><td width="40%" align="left" valign="top">glFrontFace</td><td width="20%" align="center"><a accesskey="h" href="index.xml">Home</a></td><td width="40%" align="right" valign="top">glGenLists</td></tr></table></div></body></html>
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