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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:base="" xml:id="eglQueryContext">
<info>
<copyright>
<year>2003-2014</year>
<holder>The Khronos Group Inc.</holder>
</copyright>
</info>
<refmeta>
<refentrytitle>eglQueryContext</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>eglQueryContext</refname>
<refpurpose>
return <acronym>EGL</acronym> rendering context information
</refpurpose>
</refnamediv>
<refsynopsisdiv>
<title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>EGLBoolean <function>eglQueryContext</function></funcdef>
<paramdef>EGLDisplay <parameter>display</parameter></paramdef>
<paramdef>EGLContext <parameter>context</parameter></paramdef>
<paramdef>EGLint <parameter>attribute</parameter></paramdef>
<paramdef>EGLint * <parameter>value</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 xml:id="parameters"><title>Parameters</title>
<variablelist>
<varlistentry>
<term><parameter>display</parameter></term>
<listitem>
<para>
Specifies the EGL display connection.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>context</parameter></term>
<listitem>
<para>
Specifies the EGL rendering context to query.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>attribute</parameter></term>
<listitem>
<para>
Specifies the EGL rendering context attribute to be returned.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>value</parameter></term>
<listitem>
<para>
Returns the requested value.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 xml:id="description"><title>Description</title>
<para>
<function>eglQueryContext</function> returns in
<parameter>value</parameter> the value of
<parameter>attribute</parameter> for <parameter>context</parameter>.
<parameter>attribute</parameter> can be one of the following:
</para>
<variablelist>
<varlistentry>
<term><constant>EGL_CONFIG_ID</constant></term>
<listitem><para>
Returns the ID of the EGL frame buffer configuration
with respect to which the context was created.
</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>EGL_CONTEXT_CLIENT_TYPE</constant></term>
<listitem><para>
Returns the type of client API which the context
supports (one of
<constant>EGL_OPENGL_API</constant>,
<constant>EGL_OPENGL_ES_API</constant>, or
<constant>EGL_OPENVG_API</constant>).
</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>EGL_CONTEXT_CLIENT_VERSION</constant></term>
<listitem><para>
Returns the version of the client API which the
context supports, as specified at context creation
time. The resulting value is only meaningful for an
OpenGL ES context.
</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>EGL_RENDER_BUFFER</constant></term>
<listitem>
<para>
Returns the buffer which client API rendering
via the context will use. The value returned
depends on properties of both the context, and
the surface to which the context is bound:
</para>
<itemizedlist>
<listitem><para>
If the context is bound to a pixmap surface,
then <constant>EGL_SINGLE_BUFFER</constant> will
be returned.
</para></listitem>
<listitem><para>
If the context is bound to a pbuffer surface,
then <constant>EGL_BACK_BUFFER</constant> will
be returned.
</para></listitem>
<listitem><para>
If the context is bound to a window surface,
then either <constant>EGL_BACK_BUFFER</constant>
or <constant>EGL_SINGLE_BUFFER</constant> may be
returned. The value returned depends on both the
buffer requested by the setting of the
<constant>EGL_RENDER_BUFFER</constant> property
of the surface (which may be queried by calling
<function>eglQuerySurface</function>), and on
the client API (not all client APIs support
single-buffer rendering to window surfaces).
</para></listitem>
<listitem><para>
If the context is not bound to a surface, such
as an OpenGL ES context bound to a framebuffer
object, then <constant>EGL_NONE</constant> will
be returned.
</para></listitem>
</itemizedlist>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 xml:id="notes"><title>Notes</title>
<para>
Attributes <constant>EGL_CONTEXT_CLIENT_TYPE</constant> and
<constant>EGL_RENDER_BUFFER</constant> are supported only if
the EGL version is 1.2 or greater.
</para>
<para>
Attribute <constant>EGL_CONTEXT_CLIENT_VERSION</constant> is
supported only if the EGL version is 1.3 or greater.
</para>
</refsect1>
<refsect1 xml:id="errors"><title>Errors</title>
<para>
<constant>EGL_FALSE</constant> is returned on failure,
<constant>EGL_TRUE</constant> otherwise.
<parameter>value</parameter> is not modified when
<constant>EGL_FALSE</constant> is returned.
</para>
<para>
<constant>EGL_BAD_DISPLAY</constant> is generated if
<parameter>display</parameter> is not an EGL display connection.
</para>
<para>
<constant>EGL_NOT_INITIALIZED</constant> is generated if
<parameter>display</parameter> has not been initialized.
</para>
<para>
<constant>EGL_BAD_CONTEXT</constant> is generated if
<parameter>context</parameter> is not an EGL rendering context.
</para>
<para>
<constant>EGL_BAD_ATTRIBUTE</constant> is generated if
<parameter>attribute</parameter> is not a valid context attribute.
</para>
</refsect1>
<refsect1 xml:id="seealso"><title>See Also</title>
<para>
<citerefentry><refentrytitle>eglCreateContext</refentrytitle></citerefentry>
</para>
</refsect1>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="copyright.xml"/>
</refentry>
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