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<!DOCTYPE refentry [ <!ENTITY % mathent SYSTEM "math.ent"> %mathent; ]>
<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glMapBuffer">
<info>
<copyright>
<year>2005</year>
<holder>Addison-Wesley Group</holder>
</copyright>
<copyright>
<year>2010-2014</year>
<holder>Khronos Group</holder>
</copyright>
</info>
<refmeta>
<refentrytitle>glMapBuffer</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>glMapBuffer</refname>
<refname>glMapNamedBuffer</refname>
<refpurpose>map all of a buffer object's data store into the client's address space</refpurpose>
</refnamediv>
<refsynopsisdiv><title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void *<function>glMapBuffer</function></funcdef>
<paramdef>GLenum <parameter>target</parameter></paramdef>
<paramdef>GLenum <parameter>access</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void *<function>glMapNamedBuffer</function></funcdef>
<paramdef>GLuint <parameter>buffer</parameter></paramdef>
<paramdef>GLenum <parameter>access</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 xml:id="parameters"><title>Parameters</title>
<variablelist>
<varlistentry>
<term><parameter>target</parameter></term>
<listitem>
<para>
Specifies the target to which the buffer object is bound
for <function>glMapBuffer</function>, which must be one
of the buffer binding targets in the following table:
</para>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="bufferbindings.xml"/>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>buffer</parameter></term>
<listitem>
<para>
Specifies the name of the buffer object for
<function>glMapNamedBuffer</function>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>access</parameter></term>
<listitem>
<para>
Specifies the access policy for
<function>glMapBuffer</function> and
<function>glMapNamedBuffer</function>, indicating
whether it will be possible to read from, write to, or
both read from and write to the buffer object's mapped
data store. The symbolic constant must be
<constant>GL_READ_ONLY</constant>,
<constant>GL_WRITE_ONLY</constant>, or
<constant>GL_READ_WRITE</constant>.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 xml:id="description"><title>Description</title>
<para>
<function>glMapBuffer</function> and
<function>glMapNamedBuffer</function> map the entire data store
of a specified buffer object into the client's address space.
The data can then be directly read and/or written relative to
the returned pointer, depending on the specified
<parameter>access</parameter> policy.
</para>
<para>
A pointer to the beginning of the mapped range is returned once
all pending operations on that buffer object have completed, and
may be used to modify and/or query the corresponding range of
the data store according to the value of
<parameter>access</parameter>:
<itemizedlist>
<listitem>
<para>
<constant>GL_READ_ONLY</constant> indicates that
the returned pointer may be used to read buffer
object data.
</para>
</listitem>
<listitem>
<para>
<constant>GL_WRITE_ONLY</constant> indicates that
the returned pointer may be used to modify buffer
object data.
</para>
</listitem>
<listitem>
<para>
<constant>GL_READ_WRITE</constant> indicates that
the returned pointer may be used to read and to
modify buffer object data.
</para>
</listitem>
</itemizedlist>
</para>
<para>
If an error is generated, a <code>NULL</code> pointer is
returned.
</para>
<para>
If no error occurs, the returned pointer will reflect an
allocation aligned to the value of
<constant>GL_MIN_MAP_BUFFER_ALIGNMENT</constant> basic machine
units.
</para>
<para>
The returned pointer values may not be passed as parameter
values to GL commands. For example, they may not be used to
specify array pointers, or to specify or query pixel or texture
image data; such actions produce undefined results, although
implementations may not check for such behavior for performance
reasons.
</para>
<para>
No GL error is generated if the returned pointer is accessed in
a way inconsistent with <parameter>access</parameter> (e.g. used
to read from a mapping made with <parameter>access</parameter>
<constant>GL_WRITE_ONLY</constant> or write to a mapping made
with <parameter>access</parameter>
<constant>GL_READ_ONLY</constant>), but the result is undefined
and system errors (possibly including program termination) may
occur.
</para>
<para>
Mappings to the data stores of buffer objects may have
nonstandard performance characteristics. For example, such
mappings may be marked as uncacheable regions of memory, and in
such cases reading from them may be very slow. To ensure optimal
performance, the client should use the mapping in a fashion
consistent with the values of
<constant>GL_BUFFER_USAGE</constant> for the buffer object and
of <parameter>access</parameter>. Using a mapping in a fashion
inconsistent with these values is liable to be multiple orders
of magnitude slower than using normal memory.
</para>
</refsect1>
<refsect1 xml:id="notes"><title>Notes</title>
<para>
Alignment of the returned pointer is guaranteed only if the
version of the GL version is 4.2 or greater. Also, the
<constant>GL_ATOMIC_COUNTER_BUFFER</constant> target is accepted
only if the GL version is 4.2 or greater.
</para>
<para>
The <constant>GL_DISPATCH_INDIRECT_BUFFER</constant> and
<constant>GL_SHADER_STORAGE_BUFFER</constant> targets are
available only if the GL version is 4.3 or greater.
</para>
<para>
The <constant>GL_QUERY_BUFFER</constant> target is available
only if the GL version is 4.4 or greater.
</para>
</refsect1>
<refsect1 xml:id="errors"><title>Errors</title>
<para>
<constant>GL_INVALID_ENUM</constant> is generated by
<function>glMapBuffer</function> if
<parameter>target</parameter> is not one of the buffer binding
targets listed above.
</para>
<para>
<constant>GL_INVALID_OPERATION</constant> is generated by
<function>glMapBuffer</function> if zero is bound to
<parameter>target</parameter>.
</para>
<para>
<constant>GL_INVALID_OPERATION</constant> is generated by
<function>glMapNamedBuffer</function> if
<parameter>buffer</parameter> is not the name of an existing
buffer object.
</para>
<para>
<constant>GL_INVALID_ENUM</constant> is generated if
<parameter>access</parameter> is not
<constant>GL_READ_ONLY</constant>,
<constant>GL_WRITE_ONLY</constant>, or
<constant>GL_READ_WRITE</constant>.
</para>
<para>
<constant>GL_OUT_OF_MEMORY</constant> is generated if the GL is
unable to map the buffer object's data store. This may occur for
a variety of system-specific reasons, such as the absence of
sufficient remaining virtual memory.
</para>
<para>
<constant>GL_INVALID_OPERATION</constant> is generated if the
buffer object is in a mapped state.
</para>
</refsect1>
<refsect1 xml:id="associatedgets"><title>Associated Gets</title>
<para>
<citerefentry><refentrytitle>glGetBufferPointerv</refentrytitle></citerefentry>
with argument <constant>GL_BUFFER_MAP_POINTER</constant>
</para>
<para>
<citerefentry><refentrytitle>glGetBufferParameter</refentrytitle></citerefentry>
with argument <constant>GL_BUFFER_MAPPED</constant>,
<constant>GL_BUFFER_ACCESS</constant>, or
<constant>GL_BUFFER_USAGE</constant>
</para>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
with <parameter>pname</parameter>
<constant>GL_MIN_MAP_BUFFER_ALIGNMENT</constant>. The value must
be a power of two that is at least 64.
</para>
</refsect1>
<refsect1 xml:id="versions"><title>Version Support</title>
<informaltable>
<tgroup cols="13" align="left">
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apifunchead.xml" xpointer="xpointer(/*/*)"/>
<tbody>
<row>
<entry><function>glMapBuffer</function></entry>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='20']/*)"/>
</row>
<row>
<entry><function>glMapNamedBuffer</function></entry>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='45']/*)"/>
</row>
</tbody>
</tgroup>
</informaltable>
</refsect1>
<refsect1 xml:id="seealso"><title>See Also</title>
<para>
<citerefentry><refentrytitle>glBindBuffer</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glBindBufferBase</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glBindBufferRange</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glBufferData</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glBufferSubData</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glDeleteBuffers</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glMapBufferRange</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glUnmapBuffer</refentrytitle></citerefentry>
</para>
</refsect1>
<refsect1 xml:id="Copyright"><title>Copyright</title>
<para>
Copyright <trademark class="copyright"/> 2005 Addison-Wesley.
Copyright <trademark class="copyright"/> 2010-2014 Khronos Group.
This material may be distributed subject to the terms and conditions set forth in
the Open Publication License, v 1.0, 8 June 1999.
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://opencontent.org/openpub/">http://opencontent.org/openpub/</link>.
</para>
</refsect1>
</refentry>
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