<div class="refentry" title="glViewport"><a id="glViewport"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glViewport — set the viewport</p></div><div class="refsynopsisdiv" title="C Specification"><h2>C Specification</h2><div class="funcsynopsis"><table class="funcprototype-table"><tr><td><code class="funcdef">void <b class="fsfunc">glViewport</b>(</code></td><td>GLint <var class="pdparam">x</var>, </td></tr><tr><td> </td><td>GLint <var class="pdparam">y</var>, </td></tr><tr><td> </td><td>GLsizei <var class="pdparam">width</var>, </td></tr><tr><td> </td><td>GLsizei <var class="pdparam">height</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1" title="Parameters"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term">

<em class="parameter"><code>x</code></em>,

<em class="parameter"><code>y</code></em>

</span></dt><dd><p>Specify the lower left corner of the viewport

rectangle, in pixels. The initial value is (0, 0).</p></dd><dt><span class="term">

<em class="parameter"><code>width</code></em>,

<em class="parameter"><code>height</code></em>

</span></dt><dd><p>Specify the width and height of the viewport. When

a GL context is first attached to a surface (e.g. window),

<em class="parameter"><code>width</code></em>

and

<em class="parameter"><code>height</code></em>

are set to the dimensions of that surface.</p></dd></dl></div></div><div class="refsect1" title="Description"><a id="description"></a><h2>Description</h2><p>

<code class="function">glViewport</code>

specifies the affine transformation of

<em class="replaceable"><code>x</code></em> and

<em class="replaceable"><code>y</code></em>

from normalized device coordinates to window coordinates. Let

<math overflow="scroll"><mfenced>

<msub><mi>x</mi><mi>nd</mi></msub>

<msub><mi>y</mi><mi>nd</mi></msub>

</mfenced></math>

be normalized device coordinates. Then the window coordinates

<math overflow="scroll"><mfenced>

<msub><mi>x</mi><mi>w</mi></msub>

<msub><mi>y</mi><mi>w</mi></msub>

</mfenced></math>

are computed as follows:</p><div class="informalequation"><math overflow="scroll">

<mtable><mtr><mtd>

<msub><mi>x</mi><mi>w</mi></msub>

<mgroupalign></mgroupalign>

<mo>=</mo>

<mgroupalign></mgroupalign>

<mo>(</mo>

<msub><mi>x</mi><mi>nd</mi></msub>

<mo>+</mo>

<mn>1</mn>

<mo>)</mo>

<mfrac>

<mi>width</mi>

<mn>2</mn>

</mfrac>

<mo>+</mo>

<mi>x</mi>

</mtd></mtr>

<mtr><mtd>

<msub><mi>y</mi><mi>w</mi></msub>

<mgroupalign></mgroupalign>

<mo>=</mo>

<mgroupalign></mgroupalign>

<mo>(</mo>

<msub><mi>y</mi><mi>nd</mi></msub>

<mo>+</mo>

<mn>1</mn>

<mo>)</mo>

<mfrac>

<mi>height</mi>

<mn>2</mn>

</mfrac>

<mo>+</mo>

<mi>y</mi>

</mtd></mtr></mtable>

</math></div><p>Viewport width and height are silently clamped to a range

that depends on the implementation. To query this range, call

<a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a>

with argument <code class="constant">GL_MAX_VIEWPORT_DIMS</code>.</p></div><div class="refsect1" title="Errors"><a id="errors"></a><h2>Errors</h2><p><code class="constant">GL_INVALID_VALUE</code> is generated if either

<em class="parameter"><code>width</code></em> or

<em class="parameter"><code>height</code></em> is negative.</p></div><div class="refsect1" title="Associated Gets"><a id="associatedgets"></a><h2>Associated Gets</h2><p>

<a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a>

with argument <code class="constant">GL_MAX_VIEWPORT_DIMS</code>

</p></div><div class="refsect1" title="See Also"><a id="seealso"></a><h2>See Also</h2><p>

<a class="citerefentry" href="glDepthRange"><span class="citerefentry"><span class="refentrytitle">glDepthRange</span></span></a>,

<a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a>

</p></div><div class="refsect1" title="Copyright"><a id="copyright"></a><h2>Copyright</h2><p>

Copyright © 2003-2004

Silicon Graphics, Inc. This document is licensed under the SGI

Free Software B License. For details, see

<a class="ulink" href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>.

</p></div></div>