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<?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>glViewport</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="glViewport"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glViewport — set the viewport</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">glViewport</b>(</code></td><td>GLint  </td><td><var class="pdparam">x</var>, </td></tr><tr><td> </td><td>GLint  </td><td><var class="pdparam">y</var>, </td></tr><tr><td> </td><td>GLsizei  </td><td><var class="pdparam">width</var>, </td></tr><tr><td> </td><td>GLsizei  </td><td><var class="pdparam">height</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>x</code></em>, </span><span class="term"><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>, </span><span class="term"><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 window,
                    <em class="parameter"><code>width</code></em> and <em class="parameter"><code>height</code></em> are set to the dimensions of that
                    window.
                </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
            <code class="function">glViewport</code> specifies the affine transformation of 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">x</mml:mi></mml:math>
            and 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">y</mml:mi></mml:math>
            from
            normalized device coordinates to window coordinates.
            Let 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:mfenced open="(" close=")">
                    <mml:msub><mml:mi mathvariant="italic">x</mml:mi>
                    <mml:mi mathvariant="italic">nd</mml:mi>
                    </mml:msub>
                    <mml:msub><mml:mi mathvariant="italic">y</mml:mi>
                    <mml:mi mathvariant="italic">nd</mml:mi>
                    </mml:msub>
                </mml:mfenced>
            </mml:math>
            be normalized device coordinates.
            Then the window coordinates 
            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:mfenced open="(" close=")">
                    <mml:msub><mml:mi mathvariant="italic">x</mml:mi>
                    <mml:mi mathvariant="italic">w</mml:mi>
                    </mml:msub>
                    <mml:msub><mml:mi mathvariant="italic">y</mml:mi>
                    <mml:mi mathvariant="italic">w</mml:mi>
                    </mml:msub>
                </mml:mfenced>
            </mml:math>
            are computed as follows:
        </p><p>
            </p><div class="informalequation"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:mrow>
                    <mml:msub><mml:mi mathvariant="italic">x</mml:mi>
                    <mml:mi mathvariant="italic">w</mml:mi>
                    </mml:msub>
                    <mml:mo>=</mml:mo>
                    <mml:mrow>
                        <mml:mfenced open="(" close=")">
                            <mml:mrow>
                                <mml:msub><mml:mi mathvariant="italic">x</mml:mi>
                                <mml:mi mathvariant="italic">nd</mml:mi>
                                </mml:msub>
                                <mml:mo>+</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:mfenced>
                        <mml:mo>⁢</mml:mo>
                        <mml:mfenced open="(" close=")">
                            <mml:mfrac>
                                <mml:mi mathvariant="italic">width</mml:mi>
                                <mml:mn>2</mml:mn>
                            </mml:mfrac>
                        </mml:mfenced>
                        <mml:mo>+</mml:mo>
                        <mml:mi mathvariant="italic">x</mml:mi>
                    </mml:mrow>
                </mml:mrow>
            </mml:math></div><p>
        </p><p>
            </p><div class="informalequation"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                
                <mml:mrow>
                    <mml:msub><mml:mi mathvariant="italic">y</mml:mi>
                    <mml:mi mathvariant="italic">w</mml:mi>
                    </mml:msub>
                    <mml:mo>=</mml:mo>
                    <mml:mrow>
                        <mml:mfenced open="(" close=")">
                            <mml:mrow>
                                <mml:msub><mml:mi mathvariant="italic">y</mml:mi>
                                <mml:mi mathvariant="italic">nd</mml:mi>
                                </mml:msub>
                                <mml:mo>+</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:mfenced>
                        <mml:mo>⁢</mml:mo>
                        <mml:mfenced open="(" close=")">
                            <mml:mfrac>
                                <mml:mi mathvariant="italic">height</mml:mi>
                                <mml:mn>2</mml:mn>
                            </mml:mfrac>
                        </mml:mfenced>
                        <mml:mo>+</mml:mo>
                        <mml:mi mathvariant="italic">y</mml:mi>
                    </mml:mrow>
                </mml:mrow>
            </mml:math></div><p>
        </p><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.xml"><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" lang="en" xml:lang="en"><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><p>
            <code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glViewport</code>
            is executed between the execution of <a class="citerefentry" href="glBegin.xml"><span class="citerefentry"><span class="refentrytitle">glBegin</span></span></a>
            and the corresponding execution of <a class="citerefentry" href="glEnd.xml"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>.
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p>
            <a class="citerefentry" href="glGet.xml"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_VIEWPORT</code>
        </p><p>
            <a class="citerefentry" href="glGet.xml"><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" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
            <a class="citerefentry" href="glDepthRange.xml"><span class="citerefentry"><span class="refentrytitle">glDepthRange</span></span></a>
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p>
            Copyright <span class="trademark"></span>© 1991-2006
            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></body></html>
