| 1 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd"> |
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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> |