<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
              "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
<refentry id="glViewport">
    <refmeta>
        <refmetainfo>
            <copyright>
                <year>1991-2006</year>
                <holder>Silicon Graphics, Inc.</holder>
            </copyright>
        </refmetainfo>
        <refentrytitle>glViewport</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glViewport</refname>
        <refpurpose>set the viewport</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glViewport</function></funcdef>
                <paramdef>GLint <parameter>x</parameter></paramdef>
                <paramdef>GLint <parameter>y</parameter></paramdef>
                <paramdef>GLsizei <parameter>width</parameter></paramdef>
                <paramdef>GLsizei <parameter>height</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <!-- eqn: ignoring delim $$ -->
    <refsect1 id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>x</parameter></term>
            <term><parameter>y</parameter></term>
            <listitem>
                <para>
                    Specify the lower left corner of the viewport rectangle,
                    in pixels. The initial value is (0,0).
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>width</parameter></term>
            <term><parameter>height</parameter></term>
            <listitem>
                <para>
                    Specify the width and height
                    of the viewport.
                    When a GL context is first attached to a window,
                    <parameter>width</parameter> and <parameter>height</parameter> are set to the dimensions of that
                    window.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 id="description"><title>Description</title>
        <para>
            <function>glViewport</function> specifies the affine transformation of 
            <inlineequation><mml:math><mml:mi mathvariant="italic">x</mml:mi></mml:math></inlineequation>
            and 
            <inlineequation><mml:math><mml:mi mathvariant="italic">y</mml:mi></mml:math></inlineequation>
            from
            normalized device coordinates to window coordinates.
            Let 
            <inlineequation><mml:math>
                <!-- eqn: (x sub nd, y sub nd):-->
                <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></inlineequation>
            be normalized device coordinates.
            Then the window coordinates 
            <inlineequation><mml:math>
                <!-- eqn: (x sub w, y sub w):-->
                <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></inlineequation>
            are computed as follows:
        </para>
        <para>
            <informalequation><mml:math>
                <!-- eqn: x sub w  =  ( x sub nd  +  1 ) left ( width over 2 right )  +  x:-->
                <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>&it;</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></informalequation>
        </para>
        <para>
            <informalequation><mml:math>
                <!-- eqn: y sub w  =  ( y sub nd  +  1 ) left ( height over 2 right )  +  y:-->
                <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>&it;</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></informalequation>
        </para>
        <para>
            Viewport width and height are silently clamped
            to a range that depends on the implementation.
            To query this range, call <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument
            <constant>GL_MAX_VIEWPORT_DIMS</constant>.
        </para>
    </refsect1>
    <refsect1 id="errors"><title>Errors</title>
        <para>
            <constant>GL_INVALID_VALUE</constant> is generated if either <parameter>width</parameter> or <parameter>height</parameter> is negative.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <function>glViewport</function>
            is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
            and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.
        </para>
    </refsect1>
    <refsect1 id="associatedgets"><title>Associated Gets</title>
        <para>
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_VIEWPORT</constant>
        </para>
        <para>
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_MAX_VIEWPORT_DIMS</constant>
        </para>
    </refsect1>
    <refsect1 id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glDepthRange</refentrytitle></citerefentry>
        </para>
    </refsect1>
    <refsect1 id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"></trademark> 1991-2006
            Silicon Graphics, Inc. This document is licensed under the SGI
            Free Software B License. For details, see
            <ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
        </para>
    </refsect1>
</refentry>
