xref: /third_party/EGL/sdk/docs/man/docbook4/eglQueryContext.xml

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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
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<refentry xml:base="" id="eglQueryContext">
    <refentryinfo>
         <copyright>
             <year>2003-2014</year>
             <holder>The Khronos Group Inc.</holder>
         </copyright>
    </refentryinfo>
    <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 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 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 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 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 id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>eglCreateContext</refentrytitle></citerefentry>
        </para>
    </refsect1>
    <refsect3 id="Copyright"><title></title>
        <!-- Content included from copyright.inc.xsl -->
        <imageobject>
                <imagedata fileref="KhronosLogo.jpg" format="jpg" />
        </imageobject>
        <para />
    </refsect3>
</refentry>