Return to glFrustum.xml CVS log

Up to [Development] / projects / ogl-sample / main / doc / gles / xml

OpenGL ES 1.0 and EGL 1.0 reference manual and man pages (written by
Claude Knaus, based on OpenGL SI man pages).

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook V4.2//EN" "DTD/docbook/docbookx.dtd">

<!--
  License Applicability. Except to the extent portions of this file are
  made subject to an alternative license as permitted in the SGI Free
  Software License B, Version 1.1 (the "License"), the contents of this
  file are subject only to the provisions of the License. You may not use
  this file except in compliance with the License. You may obtain a copy
  of the License at Silicon Graphics, Inc., attn: Legal Services, 1600
  Amphitheatre Parkway, Mountain View, CA 94043-1351, or at:

  http://oss.sgi.com/projects/FreeB

  Note that, as provided in the License, the Software is distributed on an
  "AS IS" basis, with ALL EXPRESS AND IMPLIED WARRANTIES AND CONDITIONS
  DISCLAIMED, INCLUDING, WITHOUT LIMITATION, ANY IMPLIED WARRANTIES AND
  CONDITIONS OF MERCHANTABILITY, SATISFACTORY QUALITY, FITNESS FOR A
  PARTICULAR PURPOSE, AND NON-INFRINGEMENT.

  Original Code. The Original Code is: OpenGL ES Reference Manual,
  Version 1.0, released September 2003, developed by Silicon Graphics,
  Inc.  The Original Code is Copyright (c) 2003 Silicon Graphics, Inc.
  Copyright in any portions created by third parties is as indicated
  elsewhere herein.  All Rights Reserved.
-->

<refentry id="glFrustum">
  <refmeta>
    <refentrytitle>glFrustum</refentrytitle>
    <manvolnum>3G</manvolnum>
  </refmeta>

  <refnamediv>
    <refdescriptor>glFrustum</refdescriptor>
    <refname>glFrustumf</refname>
    <refname>glFrustumx</refname>
    <refpurpose>multiply the current matrix by a perspective matrix</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <title>C Specification</title>

    <funcsynopsis>
      <funcprototype>
        <funcdef>void <function>glFrustumf</function></funcdef>
        <paramdef>GLfloat <parameter>left</parameter></paramdef>
        <paramdef>GLfloat <parameter>right</parameter></paramdef>
        <paramdef>GLfloat <parameter>bottom</parameter></paramdef>
        <paramdef>GLfloat <parameter>top</parameter></paramdef>
        <paramdef>GLfloat <parameter>near</parameter></paramdef>
        <paramdef>GLfloat <parameter>far</parameter></paramdef>
      </funcprototype>
      <funcprototype>
        <funcdef>void <function>glFrustumx</function></funcdef>
        <paramdef>GLfixed <parameter>left</parameter></paramdef>
        <paramdef>GLfixed <parameter>right</parameter></paramdef>
        <paramdef>GLfixed <parameter>bottom</parameter></paramdef>
        <paramdef>GLfixed <parameter>top</parameter></paramdef>
        <paramdef>GLfixed <parameter>near</parameter></paramdef>
        <paramdef>GLfixed <parameter>far</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Parameters</title>

    <variablelist>
      <varlistentry>
        <term>
        <parameter>left</parameter>, 
        <parameter>right</parameter>
        </term>

        <listitem>
          <para>Specify the coordinates for the left and right
          vertical clipping planes.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>
        <parameter>bottom</parameter>, 
        <parameter>top</parameter>
        </term>

        <listitem>
          <para>Specify the coordinates for the bottom and top
          horizontal clipping planes.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>
        <parameter>near</parameter>, 
        <parameter>far</parameter>
        </term>

        <listitem>
          <para>Specify the distances to the near and far depth
          clipping planes. Both distances must be positive.</para>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <para><function>glFrustum</function>
    describes a perspective matrix that produces a perspective
    projection. The current matrix (see 
    <citerefentry><refentrytitle>glMatrixMode</refentrytitle></citerefentry>)
    is multiplied by this matrix and the result replaces the
    current matrix, as if 
    <citerefentry><refentrytitle>glMultMatrix</refentrytitle></citerefentry>
    were called with the following matrix as its argument:</para>


    <informalequation><math>
      <mrow>
        <mo>(</mo>
        <mtable class="matrix">
          <mtr>
            <mtd>
              <mfrac>
                <mn>2</mn>
                <mrow><mi>right</mi><mo>-</mo><mi>left</mi></mrow>
              </mfrac>
            </mtd>
            <mtd><mn>0</mn></mtd>
            <mtd><mi>A</mi></mtd>
            <mtd><mn>0</mn></mtd>
          </mtr>
          <mtr>
            <mtd><mn>0</mn></mtd>
            <mtd>
              <mfrac>
                <mn>2</mn>
                <mrow><mi>top</mi><mo>-</mo><mi>bottom</mi></mrow>
              </mfrac>
            </mtd>
            <mtd><mi>B</mi></mtd>
            <mtd><mn>0</mn></mtd>
          </mtr>
          <mtr>
            <mtd><mn>0</mn></mtd>
            <mtd><mn>0</mn></mtd>
            <mtd><mi>C</mi></mtd>
            <mtd><mi>D</mi></mtd>
          </mtr>
          <mtr>
            <mtd><mn>0</mn></mtd>
            <mtd><mn>0</mn></mtd>
            <mtd><mo>-</mo><mn>1</mn></mtd>
            <mtd><mn>0</mn></mtd>
          </mtr>
        </mtable>
        <mo>)</mo>
      </mrow>
    </math></informalequation>

    <para>where</para>

    <informalequation><math><mtable>
      <mtr><mtd>
        <mi>A</mi>
        <mgroupalign/>
        <mo>=</mo>
        <mgroupalign/>
        <mo>-</mo>
        <mfrac>
          <mrow><mi>right</mi><mo>+</mo><mi>left</mi></mrow>
          <mrow><mi>right</mi><mo>-</mo><mi>left</mi></mrow>
        </mfrac>
      </mtd></mtr>
      <mtr><mtd>
        <mi>B</mi>
        <mgroupalign/>
        <mo>=</mo>
        <mgroupalign/>
        <mo>-</mo>
        <mfrac>
          <mrow><mi>top</mi><mo>+</mo><mi>bottom</mi></mrow>
          <mrow><mi>top</mi><mo>-</mo><mi>bottom</mi></mrow>
        </mfrac>
      </mtd></mtr>
      <mtr><mtd>
        <mi>C</mi>
        <mgroupalign/>
        <mo>=</mo>
        <mgroupalign/>
        <mo>-</mo>
        <mfrac>
          <mrow><mi>far</mi><mo>+</mo><mi>near</mi></mrow>
          <mrow><mi>far</mi><mo>-</mo><mi>near</mi></mrow>
        </mfrac>
      </mtd></mtr>
      <mtr><mtd>
        <mi>D</mi>
        <mgroupalign/>
        <mo>=</mo>
        <mgroupalign/>
        <mo>-</mo>
        <mfrac>
          <mrow><mn>2</mn><mi>far</mi><mi>near</mi></mrow>
          <mrow><mi>far</mi><mo>-</mo><mi>near</mi></mrow>
        </mfrac>
      </mtd></mtr>
    </mtable></math></informalequation>

    <para>Typically, the matrix mode is 
    <constant>GL_PROJECTION</constant>, and
    (<parameter>left</parameter>, <parameter>bottom</parameter>,
    -<parameter>near</parameter>) and
    (<parameter>right</parameter>, <parameter>top</parameter>,
    -<parameter>near</parameter>)
    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).
    -<parameter>far</parameter>
    specifies the location of the far clipping plane. Both 
    <parameter>near</parameter> and 
    <parameter>far</parameter> must be positive.</para>

    <para>Use 
    <citerefentry><refentrytitle>glPushMatrix</refentrytitle></citerefentry>
    and 
    <citerefentry><refentrytitle>glPopMatrix</refentrytitle></citerefentry>
    to save and restore the current matrix stack.</para>
  </refsect1>

  <refsect1>
    <title>Notes</title>

    <para>Depth buffer precision is affected by the values
    specified for <parameter>near</parameter> and 
    <parameter>far</parameter>. The greater the ratio of 
    <parameter>far</parameter> to 
    <parameter>near</parameter> 
    is, the less effective the depth buffer will be at
    distinguishing between surfaces that are near each other. If</para>

    <informalequation><math><mtable>
      <mtr><mtd>
        <mi>r</mi>
        <mo>=</mo>
        <mfrac><mi>far</mi><mi>near</mi></mfrac>
      </mtd></mtr>
    </mtable></math></informalequation>

    <para>roughly
    <inlineequation><math>
      <msub><mo>log</mo><mn>2</mn></msub><mo>(</mo><mi>r</mi><mo>)</mo>
    </math></inlineequation>
    bits of depth buffer precision are lost. Because
    <replaceable>r</replaceable> approaches infinity as 
    <parameter>near</parameter> approaches 0, 
    <parameter>near</parameter> must never be set to 0.</para>
  </refsect1>

  <refsect1>
    <title>Errors</title>

    <para>
      <constant>GL_INVALID_VALUE</constant> is generated if 
      <parameter>near</parameter> or <parameter>far</parameter>
      is not positive, or if 
      <parameter>left</parameter> = <parameter>right</parameter>, or 
      <parameter>bottom</parameter> = <parameter>top</parameter>.
    </para>
  </refsect1>

  <refsect1>
    <title>See Also</title>

    <para>
      <citerefentry><refentrytitle>glOrtho</refentrytitle></citerefentry>, 
      <citerefentry><refentrytitle>glMatrixMode</refentrytitle></citerefentry>, 
      <citerefentry><refentrytitle>glMultMatrix</refentrytitle></citerefentry>, 
      <citerefentry><refentrytitle>glPushMatrix</refentrytitle></citerefentry>, 
      <citerefentry><refentrytitle>glViewport</refentrytitle></citerefentry>
    </para>
  </refsect1>
</refentry>