upstream-man-pages/man2/xhtml/gluPerspective.xml

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   3 <?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>gluPerspective</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="gluPerspective"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>gluPerspective — set up a perspective projection matrix</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><tr><td><code class="funcdef">void <b class="fsfunc">gluPerspective</b>(</code></td><td>GLdouble  </td><td><var class="pdparam">fovy</var>, </td></tr><tr><td> </td><td>GLdouble  </td><td><var class="pdparam">aspect</var>, </td></tr><tr><td> </td><td>GLdouble  </td><td><var class="pdparam">zNear</var>, </td></tr><tr><td> </td><td>GLdouble  </td><td><var class="pdparam">zFar</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>fovy</code></em></span></dt><dd><p>
   4                     Specifies the field of view angle, in degrees, in the <span class="emphasis"><em>y</em></span> direction.
   5                 </p></dd><dt><span class="term"><em class="parameter"><code>aspect</code></em></span></dt><dd><p>
   6                     Specifies the aspect ratio that determines
   7                     the field of view in the <span class="emphasis"><em>x</em></span> direction.
   8                     The aspect ratio is the ratio of <span class="emphasis"><em>x</em></span> (width) to <span class="emphasis"><em>y</em></span> (height).
   9                 </p></dd><dt><span class="term"><em class="parameter"><code>zNear</code></em></span></dt><dd><p>
  10                     Specifies the distance from the viewer to the near clipping plane
  11                     (always positive).
  12                 </p></dd><dt><span class="term"><em class="parameter"><code>zFar</code></em></span></dt><dd><p>
  13                     Specifies the distance from the viewer to the far clipping plane
  14                     (always positive).
  15                 </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
  16             <code class="function">gluPerspective</code> specifies a viewing frustum into the world coordinate system.
  17             In general, the aspect ratio in <code class="function">gluPerspective</code> should match the aspect ratio
  18             of the associated viewport. For example,
  19             <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
  20
  21                 <mml:mrow>
  22                     <mml:mi mathvariant="italic">aspect</mml:mi>
  23                     <mml:mo>=</mml:mo>
  24                     <mml:mn>2.0</mml:mn>
  25                 </mml:mrow>
  26             </mml:math>
  27             means
  28             the viewer's
  29             angle of view is twice as wide in <span class="emphasis"><em>x</em></span> as it is in <span class="emphasis"><em>y</em></span>.
  30             If the viewport is
  31             twice as wide as it is tall, it displays the image without distortion.
  32         </p><p>
  33             The matrix generated by <code class="function">gluPerspective</code> is multipled by the current matrix,
  34             just as if <a class="citerefentry" href="glMultMatrix.xml"><span class="citerefentry"><span class="refentrytitle">glMultMatrix</span></span></a> were called with the generated matrix.
  35             To load the perspective matrix onto the current matrix stack instead,
  36             precede the call to <code class="function">gluPerspective</code> with a call to <a class="citerefentry" href="glLoadIdentity.xml"><span class="citerefentry"><span class="refentrytitle">glLoadIdentity</span></span></a>.
  37         </p><p>
  38             Given <span class="emphasis"><em>f</em></span> defined as follows:
  39         </p><p>
  40             </p><div class="informalequation"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
  41
  42                 <mml:mrow>
  43                     <mml:mi mathvariant="italic">f</mml:mi>
  44                     <mml:mo>=</mml:mo>
  45                     <mml:mrow>
  46                         <mml:mi mathvariant="italic">cotangent</mml:mi>
  47                         <mml:mo>⁡</mml:mo>
  48                         <mml:mfenced open="(" close=")">
  49                             <mml:mfrac>
  50                                 <mml:mi mathvariant="italic">fovy</mml:mi>
  51                                 <mml:mn>2</mml:mn>
  52                             </mml:mfrac>
  53                         </mml:mfenced>
  54                     </mml:mrow>
  55                 </mml:mrow>
  56             </mml:math></div><p>
  57             The generated matrix is
  58         </p><p>
  59             </p><div class="informalequation"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
  60
  61                 <mml:mfenced open="(" close=")">
  62                     <mml:mtable>
  63                         <mml:mtr>
  64                             <mml:mtd>
  65                                 <mml:mfrac>
  66                                     <mml:mi mathvariant="italic">f</mml:mi>
  67                                     <mml:mi mathvariant="italic">aspect</mml:mi>
  68                                 </mml:mfrac>
  69                             </mml:mtd>
  70                             <mml:mtd>
  71                                 <mml:mn>0</mml:mn>
  72                             </mml:mtd>
  73                             <mml:mtd>
  74                                 <mml:mn>0</mml:mn>
  75                             </mml:mtd>
  76                             <mml:mtd>
  77                                 <mml:mn>0</mml:mn>
  78                             </mml:mtd>
  79                         </mml:mtr>
  80                         <mml:mtr>
  81                             <mml:mtd>
  82                                 <mml:mn>0</mml:mn>
  83                             </mml:mtd>
  84                             <mml:mtd>
  85                                 <mml:mi mathvariant="italic">f</mml:mi>
  86                             </mml:mtd>
  87                             <mml:mtd>
  88                                 <mml:mn>0</mml:mn>
  89                             </mml:mtd>
  90                             <mml:mtd>
  91                                 <mml:mn>0</mml:mn>
  92                             </mml:mtd>
  93                         </mml:mtr>
  94                         <mml:mtr>
  95                             <mml:mtd>
  96                                 <mml:mn>0</mml:mn>
  97                             </mml:mtd>
  98                             <mml:mtd>
  99                                 <mml:mn>0</mml:mn>
 100                             </mml:mtd>
 101                             <mml:mtd>
 102                                 <mml:mfrac>
 103                                     <mml:mfenced open="" close="">
 104                                         <mml:mrow>
 105                                             <mml:mi mathvariant="italic">zFar</mml:mi>
 106                                             <mml:mo>+</mml:mo>
 107                                             <mml:mi mathvariant="italic">zNear</mml:mi>
 108                                         </mml:mrow>
 109                                     </mml:mfenced>
 110                                     <mml:mfenced open="" close="">
 111                                         <mml:mrow>
 112                                             <mml:mi mathvariant="italic">zNear</mml:mi>
 113                                             <mml:mo>-</mml:mo>
 114                                             <mml:mi mathvariant="italic">zFar</mml:mi>
 115                                         </mml:mrow>
 116                                     </mml:mfenced>
 117                                 </mml:mfrac>
 118                             </mml:mtd>
 119                             <mml:mtd>
 120                                 <mml:mfrac>
 121                                     <mml:mfenced open="" close="">
 122                                         <mml:mrow>
 123                                             <mml:mn>2</mml:mn>
 124                                             <mml:mo>×</mml:mo>
 125                                             <mml:mi mathvariant="italic">zFar</mml:mi>
 126                                             <mml:mo>×</mml:mo>
 127                                             <mml:mi mathvariant="italic">zNear</mml:mi>
 128                                         </mml:mrow>
 129                                     </mml:mfenced>
 130                                     <mml:mfenced open="" close="">
 131                                         <mml:mrow>
 132                                             <mml:mi mathvariant="italic">zNear</mml:mi>
 133                                             <mml:mo>-</mml:mo>
 134                                             <mml:mi mathvariant="italic">zFar</mml:mi>
 135                                         </mml:mrow>
 136                                     </mml:mfenced>
 137                                 </mml:mfrac>
 138                             </mml:mtd>
 139                         </mml:mtr>
 140                         <mml:mtr>
 141                             <mml:mtd>
 142                                 <mml:mn>0</mml:mn>
 143                             </mml:mtd>
 144                             <mml:mtd>
 145                                 <mml:mn>0</mml:mn>
 146                             </mml:mtd>
 147                             <mml:mtd>
 148                                 <mml:mn>-1</mml:mn>
 149                             </mml:mtd>
 150                             <mml:mtd>
 151                                 <mml:mn>0</mml:mn>
 152                             </mml:mtd>
 153                         </mml:mtr>
 154                     </mml:mtable>
 155                 </mml:mfenced>
 156             </mml:math></div><p>
 157         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p>
 158             Depth buffer precision is affected by the values specified for
 159             <em class="parameter"><code>zNear</code></em> and <em class="parameter"><code>zFar</code></em>.
 160             The greater the ratio of <em class="parameter"><code>zFar</code></em> to <em class="parameter"><code>zNear</code></em> is,
 161             the less effective the depth buffer will be at distinguishing between
 162             surfaces that are near each other.
 163             If
 164         </p><p>
 165             <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
 166
 167                 <mml:mrow>
 168                     <mml:mi mathvariant="italic">r</mml:mi>
 169                     <mml:mo>=</mml:mo>
 170                     <mml:mfrac>
 171                         <mml:mi mathvariant="italic">zFar</mml:mi>
 172                         <mml:mi mathvariant="italic">zNear</mml:mi>
 173                     </mml:mfrac>
 174                 </mml:mrow>
 175             </mml:math>
 176         </p><p>
 177         </p><p>
 178             roughly
 179             <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
 180
 181                 <mml:mrow>
 182                     <mml:msub><mml:mi mathvariant="italic">log</mml:mi>
 183                     <mml:mn>2</mml:mn>
 184                     </mml:msub>
 185                     <mml:mo>⁡</mml:mo>
 186                     <mml:mfenced open="(" close=")">
 187                         <mml:mi mathvariant="italic">r</mml:mi>
 188                     </mml:mfenced>
 189                 </mml:mrow>
 190             </mml:math>
 191             bits of depth buffer precision are lost.
 192             Because
 193             <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">r</mml:mi></mml:math>
 194             approaches infinity as <em class="parameter"><code>zNear</code></em> approaches 0,
 195             <em class="parameter"><code>zNear</code></em> must never be set to 0.
 196         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
 197             <a class="citerefentry" href="gluOrtho2D.xml"><span class="citerefentry"><span class="refentrytitle">gluOrtho2D</span></span></a>,
 198             <a class="citerefentry" href="glFrustum.xml"><span class="citerefentry"><span class="refentrytitle">glFrustum</span></span></a>,
 199             <a class="citerefentry" href="glLoadIdentity.xml"><span class="citerefentry"><span class="refentrytitle">glLoadIdentity</span></span></a>,
 200             <a class="citerefentry" href="glMultMatrix.xml"><span class="citerefentry"><span class="refentrytitle">glMultMatrix</span></span></a>
 201         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p>
 202             Copyright <span class="trademark"></span>© 1991-2006
 203             Silicon Graphics, Inc. This document is licensed under the SGI
 204             Free Software B License. For details, see
 205             <a class="ulink" href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>.
 206         </p></div></div></body></html>