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<?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="glScissor">
<refentryinfo>
<copyright>
<year>1991-2006</year>
<holder>Silicon Graphics, Inc.</holder>
</copyright>
<copyright>
<year>2010-2013</year>
<holder>Khronos Group</holder>
</copyright>
</refentryinfo>
<refmeta>
<refentrytitle>glScissor</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>glScissor</refname>
<refpurpose>define the scissor box</refpurpose>
</refnamediv>
<refsynopsisdiv><title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>glScissor</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>
<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 scissor box.
Initially (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 scissor box.
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>glScissor</function> defines a rectangle, called the scissor box,
in window coordinates.
The first two arguments,
<parameter>x</parameter> and <parameter>y</parameter>,
specify the lower left corner of the box.
<parameter>width</parameter> and <parameter>height</parameter> specify the width and height of the box.
</para>
<para>
To enable and disable the scissor test, call
<citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry> with argument
<constant>GL_SCISSOR_TEST</constant>. The test is initially disabled.
While the test is enabled, only pixels that lie within the scissor box
can be modified by drawing commands.
Window coordinates have integer values at the shared corners of
frame buffer pixels.
<code>glScissor(0,0,1,1)</code> allows modification of only the lower left
pixel in the window, and <code>glScissor(0,0,0,0)</code> doesn't allow
modification of any pixels in the window.
</para>
<para>
When the scissor test is disabled,
it is as though the scissor box includes the entire window.
</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>
</refsect1>
<refsect1 id="associatedgets"><title>Associated Gets</title>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_SCISSOR_BOX</constant>
</para>
<para>
<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_SCISSOR_TEST</constant>
</para>
</refsect1>
<refsect1 id="seealso"><title>See Also</title>
<para>
<citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glViewport</refentrytitle></citerefentry>
</para>
</refsect1>
<refsect1 id="Copyright"><title>Copyright</title>
<para>
Copyright <trademark class="copyright"></trademark> 1991-2006 Silicon Graphics, Inc.
Copyright <trademark class="copyright"></trademark> 2010-2013 Khronos Group.
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>
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