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187 lines
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XML
187 lines
10 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
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"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
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<refentry id="glMapBuffer">
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<refentryinfo>
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<copyright>
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<year>2013</year>
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<holder>Khronos Group</holder>
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</copyright>
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<copyright>
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<year>2010-2013</year>
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<holder>Khronos Group</holder>
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</copyright>
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</refentryinfo>
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<refmeta>
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<refentrytitle>glMapBuffer</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glMapBuffer</refname>
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<refpurpose>map a buffer object's data store</refpurpose>
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</refnamediv>
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<refsynopsisdiv><title>C Specification</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void * <function>glMapBuffer</function></funcdef>
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<paramdef>GLenum <parameter>target</parameter></paramdef>
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<paramdef>GLenum <parameter>access</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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<funcsynopsis>
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<funcprototype>
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<funcdef>GLboolean <function>glUnmapBuffer</function></funcdef>
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<paramdef>GLenum <parameter>target</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1 id="parameters"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>target</parameter></term>
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<listitem>
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<para>
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Specifies the target buffer object being mapped.
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The symbolic constant must be
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<constant>GL_ARRAY_BUFFER</constant>,
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<constant>GL_ATOMIC_COUNTER_BUFFER</constant>,
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<constant>GL_COPY_READ_BUFFER</constant>,
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<constant>GL_COPY_WRITE_BUFFER</constant>,
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<constant>GL_DRAW_INDIRECT_BUFFER</constant>,
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<constant>GL_DISPATCH_INDIRECT_BUFFER</constant>,
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<constant>GL_ELEMENT_ARRAY_BUFFER</constant>,
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<constant>GL_PIXEL_PACK_BUFFER</constant>,
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<constant>GL_PIXEL_UNPACK_BUFFER</constant>,
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<constant>GL_QUERY_BUFFER</constant>,
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<constant>GL_SHADER_STORAGE_BUFFER</constant>,
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<constant>GL_TEXTURE_BUFFER</constant>,
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<constant>GL_TRANSFORM_FEEDBACK_BUFFER</constant> or
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<constant>GL_UNIFORM_BUFFER</constant>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>access</parameter></term>
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<listitem>
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<para>
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For <function>glMapBuffer</function> only,
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specifies the access policy, indicating whether it will be possible to read from, write to,
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or both read from and write to the buffer object's mapped data store. The symbolic constant must be
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<constant>GL_READ_ONLY</constant>, <constant>GL_WRITE_ONLY</constant>, or <constant>GL_READ_WRITE</constant>.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1 id="description"><title>Description</title>
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<para>
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<function>glMapBuffer</function> maps to the client's address space the entire data store of the buffer object
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currently bound to <parameter>target</parameter>. The data can then be directly read and/or written relative to
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the returned pointer, depending on the specified <parameter>access</parameter> policy. If the GL is unable to
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map the buffer object's data store, <function>glMapBuffer</function> generates an error and returns
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<constant>NULL</constant>. This may occur for system-specific reasons, such as low virtual memory availability.
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If no error occurs, the returned pointer will have an alignment of at least <constant>GL_MIN_MAP_BUFFER_ALIGNMENT</constant>
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basic machine units. The value of <constant>GL_MIN_MAP_BUFFER_ALIGNMENT</constant> can be retrieved by calling
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with <parameter>pname</parameter> set to
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<constant>GL_MIN_MAP_BUFFER_ALIGNMENT</constant> and must be a power of two that is at least 64.
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</para>
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<para>
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If a mapped data store is accessed in a way inconsistent with the specified <parameter>access</parameter> policy,
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no error is generated, but performance may be negatively impacted and system errors, including program
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termination, may result. Unlike the <parameter>usage</parameter> parameter of <function>glBufferData</function>,
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<parameter>access</parameter> is not a hint, and does in fact constrain the usage of the mapped data store on
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some GL implementations. In order to achieve the highest performance available, a buffer object's data store
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should be used in ways consistent with both its specified <parameter>usage</parameter> and
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<parameter>access</parameter> parameters.
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</para>
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<para>
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A mapped data store must be unmapped with <function>glUnmapBuffer</function> before its buffer object is used.
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Otherwise an error will be generated by any GL command that attempts to dereference the buffer object's data store.
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When a data store is unmapped, the pointer to its data store becomes invalid. <function>glUnmapBuffer</function>
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returns <constant>GL_TRUE</constant> unless the data store contents have become corrupt during the time
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the data store was mapped. This can occur for system-specific reasons that affect the availability of graphics
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memory, such as screen mode changes. In such situations, <constant>GL_FALSE</constant> is returned and the
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data store contents are undefined. An application must detect this rare condition and reinitialize the data store.
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</para>
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<para>
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A buffer object's mapped data store is automatically unmapped when the buffer object is deleted or its data store
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is recreated with <function>glBufferData</function>.
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</para>
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</refsect1>
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<refsect1 id="notes"><title>Notes</title>
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<para>
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If an error is generated, <function>glMapBuffer</function> returns <constant>NULL</constant>, and
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<function>glUnmapBuffer</function> returns <constant>GL_FALSE</constant>.
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</para>
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<para>
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Parameter values passed to GL commands may not be sourced from the returned pointer. No error will be generated,
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but results will be undefined and will likely vary across GL implementations.
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</para>
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<para>
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Alignment of the returned pointer is guaranteed only if the version
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of the GL version is 4.2 or greater. Also, the <constant>GL_ATOMIC_COUNTER_BUFFER</constant>
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target is accepted only if the GL version is 4.2 or greater.
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</para>
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<para>
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The <constant>GL_DISPATCH_INDIRECT_BUFFER</constant> and <constant>GL_SHADER_STORAGE_BUFFER</constant> targets are available only if the GL version
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is 4.3 or greater.
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</para>
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<para>
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The <constant>GL_QUERY_BUFFER</constant> target is available only if the GL version is 4.4 or greater.
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</para>
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</refsect1>
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<refsect1 id="errors"><title>Errors</title>
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<para>
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<constant>GL_INVALID_ENUM</constant> is generated if <parameter>target</parameter> is not
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one of the accepted targets.
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</para>
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<para>
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<constant>GL_INVALID_ENUM</constant> is generated if <parameter>access</parameter> is not
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<constant>GL_READ_ONLY</constant>, <constant>GL_WRITE_ONLY</constant>, or <constant>GL_READ_WRITE</constant>.
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</para>
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<para>
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<constant>GL_OUT_OF_MEMORY</constant> is generated when <function>glMapBuffer</function> is executed
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if the GL is unable to map the buffer object's data store. This may occur for a variety of system-specific
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reasons, such as the absence of sufficient remaining virtual memory.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if the reserved buffer object name 0 is bound to <parameter>target</parameter>.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <function>glMapBuffer</function> is executed for
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a buffer object whose data store is already mapped.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <function>glUnmapBuffer</function> is executed for
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a buffer object whose data store is not currently mapped.
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</para>
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</refsect1>
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<refsect1 id="associatedgets"><title>Associated Gets</title>
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<para>
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<citerefentry><refentrytitle>glGetBufferPointerv</refentrytitle></citerefentry> with argument <constant>GL_BUFFER_MAP_POINTER</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGetBufferParameter</refentrytitle></citerefentry> with argument <constant>GL_BUFFER_MAPPED</constant>, <constant>GL_BUFFER_ACCESS</constant>, or <constant>GL_BUFFER_USAGE</constant>
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</para>
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</refsect1>
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<refsect1 id="seealso"><title>See Also</title>
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<para>
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<citerefentry><refentrytitle>glBindBuffer</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glBindBufferBase</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glBindBufferRange</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glBufferData</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glBufferSubData</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glDeleteBuffers</refentrytitle></citerefentry>
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</para>
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</refsect1>
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<refsect1 id="Copyright"><title>Copyright</title>
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<para>
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Copyright <trademark class="copyright"></trademark> 2005 Addison-Wesley.
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Copyright <trademark class="copyright"></trademark> 2010-2013 Khronos Group.
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This material may be distributed subject to the terms and conditions set forth in
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the Open Publication License, v 1.0, 8 June 1999.
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<ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
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</para>
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</refsect1>
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</refentry>
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