| 1 | <?xml version="1.0" encoding="UTF-8"?> |
| 2 | <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN" |
| 3 | "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd"> |
| 4 | <refentry id="glMapBuffer"> |
| 5 | <refmeta> |
| 6 | <refmetainfo> |
| 7 | <copyright> |
| 8 | <year>2005</year> |
| 9 | <holder>Sams Publishing</holder> |
| 10 | </copyright> |
| 11 | </refmetainfo> |
| 12 | <refentrytitle>glMapBuffer</refentrytitle> |
| 13 | <manvolnum>3G</manvolnum> |
| 14 | </refmeta> |
| 15 | <refnamediv> |
| 16 | <refname>glMapBuffer</refname> |
| 17 | <refpurpose>map a buffer object's data store</refpurpose> |
| 18 | </refnamediv> |
| 19 | <refsynopsisdiv><title>C Specification</title> |
| 20 | <funcsynopsis> |
| 21 | <funcprototype> |
| 22 | <funcdef>void * <function>glMapBuffer</function></funcdef> |
| 23 | <paramdef>GLenum <parameter>target</parameter></paramdef> |
| 24 | <paramdef>GLenum <parameter>access</parameter></paramdef> |
| 25 | </funcprototype> |
| 26 | </funcsynopsis> |
| 27 | </refsynopsisdiv> |
| 28 | <refsect1 id="parameters"><title>Parameters</title> |
| 29 | <variablelist> |
| 30 | <varlistentry> |
| 31 | <term><parameter>target</parameter></term> |
| 32 | <listitem> |
| 33 | <para> |
| 34 | Specifies the target buffer object being mapped. |
| 35 | The symbolic constant must be |
| 36 | <constant>GL_ARRAY_BUFFER</constant>, |
| 37 | <constant>GL_ELEMENT_ARRAY_BUFFER</constant>, |
| 38 | <constant>GL_PIXEL_PACK_BUFFER</constant>, or |
| 39 | <constant>GL_PIXEL_UNPACK_BUFFER</constant>. |
| 40 | </para> |
| 41 | </listitem> |
| 42 | </varlistentry> |
| 43 | <varlistentry> |
| 44 | <term><parameter>access</parameter></term> |
| 45 | <listitem> |
| 46 | <para> |
| 47 | Specifies the access policy, indicating whether it will be possible to read from, write to, |
| 48 | or both read from and write to the buffer object's mapped data store. The symbolic constant must be |
| 49 | <constant>GL_READ_ONLY</constant>, <constant>GL_WRITE_ONLY</constant>, or <constant>GL_READ_WRITE</constant>. |
| 50 | </para> |
| 51 | </listitem> |
| 52 | </varlistentry> |
| 53 | </variablelist> |
| 54 | </refsect1> |
| 55 | <refsynopsisdiv><title>C Specification</title> |
| 56 | <funcsynopsis> |
| 57 | <funcprototype> |
| 58 | <funcdef>GLboolean <function>glUnmapBuffer</function></funcdef> |
| 59 | <paramdef>GLenum <parameter>target</parameter></paramdef> |
| 60 | </funcprototype> |
| 61 | </funcsynopsis> |
| 62 | </refsynopsisdiv> |
| 63 | <!-- eqn: ignoring delim $$ --> |
| 64 | <refsect1 id="parameters2"><title>Parameters</title> |
| 65 | <variablelist> |
| 66 | <varlistentry> |
| 67 | <term><parameter>target</parameter></term> |
| 68 | <listitem> |
| 69 | <para> |
| 70 | Specifies the target buffer object being unmapped. |
| 71 | The symbolic constant must be |
| 72 | <constant>GL_ARRAY_BUFFER</constant>, |
| 73 | <constant>GL_ELEMENT_ARRAY_BUFFER</constant>, |
| 74 | <constant>GL_PIXEL_PACK_BUFFER</constant>, or |
| 75 | <constant>GL_PIXEL_UNPACK_BUFFER</constant>. |
| 76 | </para> |
| 77 | </listitem> |
| 78 | </varlistentry> |
| 79 | </variablelist> |
| 80 | </refsect1> |
| 81 | <refsect1 id="description"><title>Description</title> |
| 82 | <para> |
| 83 | <function>glMapBuffer</function> maps to the client's address space the entire data store of the buffer object |
| 84 | currently bound to <parameter>target</parameter>. The data can then be directly read and/or written relative to |
| 85 | the returned pointer, depending on the specified <parameter>access</parameter> policy. If the GL is unable to |
| 86 | map the buffer object's data store, <function>glMapBuffer</function> generates an error and returns |
| 87 | <constant>NULL</constant>. This may occur for system-specific reasons, such as low virtual memory availability. |
| 88 | </para> |
| 89 | <para> |
| 90 | If a mapped data store is accessed in a way inconsistent with the specified <parameter>access</parameter> policy, |
| 91 | no error is generated, but performance may be negatively impacted and system errors, including program |
| 92 | termination, may result. Unlike the <parameter>usage</parameter> parameter of <function>glBufferData</function>, |
| 93 | <parameter>access</parameter> is not a hint, and does in fact constrain the usage of the mapped data store on |
| 94 | some GL implementations. In order to achieve the highest performance available, a buffer object's data store |
| 95 | should be used in ways consistent with both its specified <parameter>usage</parameter> and |
| 96 | <parameter>access</parameter> parameters. |
| 97 | </para> |
| 98 | <para> |
| 99 | A mapped data store must be unmapped with <function>glUnmapBuffer</function> before its buffer object is used. |
| 100 | Otherwise an error will be generated by any GL command that attempts to dereference the buffer object's data store. |
| 101 | When a data store is unmapped, the pointer to its data store becomes invalid. <function>glUnmapBuffer</function> |
| 102 | returns <constant>GL_TRUE</constant> unless the data store contents have become corrupt during the time |
| 103 | the data store was mapped. This can occur for system-specific reasons that affect the availability of graphics |
| 104 | memory, such as screen mode changes. In such situations, <constant>GL_FALSE</constant> is returned and the |
| 105 | data store contents are undefined. An application must detect this rare condition and reinitialize the data store. |
| 106 | </para> |
| 107 | <para> |
| 108 | A buffer object's mapped data store is automatically unmapped when the buffer object is deleted or its data store |
| 109 | is recreated with <function>glBufferData</function>. |
| 110 | </para> |
| 111 | </refsect1> |
| 112 | <refsect1 id="notes"><title>Notes</title> |
| 113 | <para> |
| 114 | If an error is generated, <function>glMapBuffer</function> returns <constant>NULL</constant>, and |
| 115 | <function>glUnmapBuffer</function> returns <constant>GL_FALSE</constant>. |
| 116 | </para> |
| 117 | <para> |
| 118 | <function>glMapBuffer</function> and <function>glUnmapBuffer</function> are available only if the GL version is 1.5 or greater. |
| 119 | </para> |
| 120 | <para> |
| 121 | <constant>GL_PIXEL_PACK_BUFFER</constant> and <constant>GL_PIXEL_UNPACK_BUFFER</constant> are |
| 122 | available only if the GL version is 2.1 or greater. |
| 123 | </para> |
| 124 | <para> |
| 125 | Parameter values passed to GL commands may not be sourced from the returned pointer. No error will be generated, |
| 126 | but results will be undefined and will likely vary across GL implementations. |
| 127 | </para> |
| 128 | </refsect1> |
| 129 | <refsect1 id="errors"><title>Errors</title> |
| 130 | <para> |
| 131 | <constant>GL_INVALID_ENUM</constant> is generated if <parameter>target</parameter> is not |
| 132 | <constant>GL_ARRAY_BUFFER</constant>, <constant>GL_ELEMENT_ARRAY_BUFFER</constant>, |
| 133 | <constant>GL_PIXEL_PACK_BUFFER</constant>, or <constant>GL_PIXEL_UNPACK_BUFFER</constant>. |
| 134 | </para> |
| 135 | <para> |
| 136 | <constant>GL_INVALID_ENUM</constant> is generated if <parameter>access</parameter> is not |
| 137 | <constant>GL_READ_ONLY</constant>, <constant>GL_WRITE_ONLY</constant>, or <constant>GL_READ_WRITE</constant>. |
| 138 | </para> |
| 139 | <para> |
| 140 | <constant>GL_OUT_OF_MEMORY</constant> is generated when <function>glMapBuffer</function> is executed |
| 141 | if the GL is unable to map the buffer object's data store. This may occur for a variety of system-specific |
| 142 | reasons, such as the absence of sufficient remaining virtual memory. |
| 143 | </para> |
| 144 | <para> |
| 145 | <constant>GL_INVALID_OPERATION</constant> is generated if the reserved buffer object name 0 is bound to <parameter>target</parameter>. |
| 146 | </para> |
| 147 | <para> |
| 148 | <constant>GL_INVALID_OPERATION</constant> is generated if <function>glMapBuffer</function> is executed for |
| 149 | a buffer object whose data store is already mapped. |
| 150 | </para> |
| 151 | <para> |
| 152 | <constant>GL_INVALID_OPERATION</constant> is generated if <function>glUnmapBuffer</function> is executed for |
| 153 | a buffer object whose data store is not currently mapped. |
| 154 | </para> |
| 155 | <para> |
| 156 | <constant>GL_INVALID_OPERATION</constant> is generated if <function>glMapBuffer</function> or <function>glUnmapBuffer</function> is executed |
| 157 | between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry> and the corresponding |
| 158 | execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>. |
| 159 | </para> |
| 160 | </refsect1> |
| 161 | <refsect1 id="associatedgets"><title>Associated Gets</title> |
| 162 | <para> |
| 163 | <citerefentry><refentrytitle>glGetBufferPointerv</refentrytitle></citerefentry> with argument <constant>GL_BUFFER_MAP_POINTER</constant> |
| 164 | </para> |
| 165 | <para> |
| 166 | <citerefentry><refentrytitle>glGetBufferParameteriv</refentrytitle></citerefentry> with argument <constant>GL_BUFFER_MAPPED</constant>, <constant>GL_BUFFER_ACCESS</constant>, or <constant>GL_BUFFER_USAGE</constant> |
| 167 | </para> |
| 168 | </refsect1> |
| 169 | <refsect1 id="seealso"><title>See Also</title> |
| 170 | <para> |
| 171 | <citerefentry><refentrytitle>glBindBuffer</refentrytitle></citerefentry>, |
| 172 | <citerefentry><refentrytitle>glBufferData</refentrytitle></citerefentry>, |
| 173 | <citerefentry><refentrytitle>glBufferSubData</refentrytitle></citerefentry>, |
| 174 | <citerefentry><refentrytitle>glDeleteBuffers</refentrytitle></citerefentry> |
| 175 | </para> |
| 176 | </refsect1> |
| 177 | <refsect1 id="Copyright"><title>Copyright</title> |
| 178 | <para> |
| 179 | Copyright <trademark class="copyright"></trademark> 2005 Addison-Wesley. |
| 180 | This material may be distributed subject to the terms and conditions set forth in |
| 181 | the Open Publication License, v 1.0, 8 June 1999. |
| 182 | <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>. |
| 183 | </para> |
| 184 | </refsect1> |
| 185 | </refentry> |