1Name 2 3 ARB_map_buffer_range 4 5Name Strings 6 7 GL_ARB_map_buffer_range 8 9Contributors 10 11 Chris Niederauer, Apple (ccn 'at' apple.com) 12 Rob Barris (rbarris 'at' gmail.com) 13 Michael Gold, NVIDIA 14 15Notice 16 17 Copyright (c) 2008-2013 The Khronos Group Inc. Copyright terms at 18 http://www.khronos.org/registry/speccopyright.html 19 20Specification Update Policy 21 22 Khronos-approved extension specifications are updated in response to 23 issues and bugs prioritized by the Khronos OpenGL Working Group. For 24 extensions which have been promoted to a core Specification, fixes will 25 first appear in the latest version of that core Specification, and will 26 eventually be backported to the extension document. This policy is 27 described in more detail at 28 https://www.khronos.org/registry/OpenGL/docs/update_policy.php 29 30Status 31 32 Approved by the ARB on July 11, 2008 33 34Version 35 36 Last Modified Date: June 22, 2012 37 Author Revision: 5 38 39Number 40 41 ARB Extension #50 42 43Dependencies 44 45 OpenGL 2.1 is required. 46 47 If ARB_pixel_buffer_object is NOT supported and the OpenGL version is less 48 than 2.1, ignore references to PIXEL_UNPACK_BUFFER and PIXEL_PACK_BUFFER. 49 50 If EXT_texture_buffer_object is NOT supported, ignore references to 51 TEXTURE_BUFFER_EXT. 52 53 If GL_EXT_bindable_uniform is NOT supported, ignore references to 54 UNIFORM_BUFFER_EXT. 55 56 Written based on the wording of the OpenGL 2.1 specification. 57 58 59Overview 60 61 ARB_map_buffer_range expands the buffer object API to allow greater 62 performance when a client application only needs to write to a sub-range 63 of a buffer object. To that end, this extension introduces two new buffer 64 object features: non-serialized buffer modification and explicit sub-range 65 flushing for mapped buffer objects. 66 67 OpenGL requires that commands occur in a FIFO manner meaning that any 68 changes to buffer objects either block until the data has been processed by 69 the OpenGL pipeline or else create extra copies to avoid such a block. By 70 providing a method to asynchronously modify buffer object data, an 71 application is then able to manage the synchronization points themselves 72 and modify ranges of data contained by a buffer object even though OpenGL 73 might still be using other parts of it. 74 75 This extension also provides a method for explicitly flushing ranges of a 76 mapped buffer object so OpenGL does not have to assume that the entire 77 range may have been modified. Further, it allows the application to more 78 precisely specify its intent with respect to reading, writing, and whether 79 the previous contents of a mapped range of interest need be preserved 80 prior to modification. 81 82 Affects ARB_vertex_buffer_object, ARB_pixel_buffer_object and OpenGL 1.5 83 Buffer Objects. 84 85 86Issues 87 88 (1) Why don't the new tokens and entry points in this extension have 89 "ARB" suffixes like other ARB extensions? 90 91 RESOLVED: Unlike a normal ARB extension, this is a strict subset 92 of functionality already approved in OpenGL 3.0. This extension 93 exists only to support that functionality on older hardware that 94 cannot implement a full OpenGL 3.0 driver. Since there are no 95 possible behavior changes between the ARB extension and core 96 features, source code compatibility is improved by not using 97 suffixes on the extension. 98 99 100New Procedures and Functions 101 102 void *MapBufferRange( enum target, intptr offset, sizeiptr length, 103 bitfield access ); 104 105 void FlushMappedBufferRange( enum target, intptr offset, sizeiptr length ); 106 107 108New Tokens 109 110 Accepted by the <access> parameter of MapBufferRange: 111 112 MAP_READ_BIT 0x0001 113 MAP_WRITE_BIT 0x0002 114 MAP_INVALIDATE_RANGE_BIT 0x0004 115 MAP_INVALIDATE_BUFFER_BIT 0x0008 116 MAP_FLUSH_EXPLICIT_BIT 0x0010 117 MAP_UNSYNCHRONIZED_BIT 0x0020 118 119 120Additions to Chapter 2 of the OpenGL 2.1 Specification (Buffer Objects) 121 122 Add to the end of Section 2.9 (p. 38): 123 124 All or part of the data store of a buffer object may be mapped into the 125 client's address space by calling 126 127 void *MapBufferRange( enum target, intptr offset, sizeiptr length, 128 bitfield access ); 129 130 with <target> set to one of ARRAY_BUFFER, ELEMENT_ARRAY_BUFFER, 131 PIXEL_UNPACK_BUFFER, PIXEL_PACK_BUFFER, TEXTURE_BUFFER_EXT, or 132 UNIFORM_BUFFER_EXT. <offset> and <length> indicate the range of data in the 133 buffer object that is to be mapped, in terms of basic machine units. 134 <access> is a bitfield containing flags which describe the requested 135 mapping. These flags are described below. 136 137 If no error occurs, a pointer to the beginning of the mapped range is 138 returned and may be used to modify and/or query the corresponding range of 139 the buffer, according to the access flags. 140 141 MAP_READ_BIT indicates that the returned pointer may be used to read buffer 142 object data. No GL error is generated if the pointer is used to query a 143 mapping which excludes this flag, but the result is undefined and system 144 errors (possibly including program termination) may occur. 145 146 MAP_WRITE_BIT indicates that the returned pointer may be used to modify 147 buffer object data. No GL error is generated if the pointer is used to 148 modify a mapping which excludes this flag, but the result is undefined and 149 system errors (possibly including program termination) may occur. 150 151 The following optional flags in <access> may be used to modify the mapping: 152 153 MAP_INVALIDATE_RANGE_BIT indicates that the previous contents of the 154 specified range may be discarded. Data within this range is undefined with 155 the exception of subsequently written data. No GL error is generated if 156 subsequent GL operations access unwritten data, but the result is undefined 157 and system errors (possibly including program termination) may occur. This 158 flag may not be used in combination with MAP_READ_BIT. 159 160 MAP_INVALIDATE_BUFFER_BIT indicates that the previous contents of the entire 161 buffer may be discarded. Data within the entire buffer is undefined with the 162 exception of subsequently written data. No GL error is generated if 163 subsequent GL operations access unwritten data, but the result is undefined 164 and system errors (possibly including program termination) may occur. This 165 flag may not be used in combination with MAP_READ_BIT. 166 167 MAP_FLUSH_EXPLICIT_BIT indicates that one or more discrete subranges of the 168 mapping may be modified. When this flag is set, modifications to each 169 subrange must be explicitly flushed by calling FlushMappedBufferRange. No 170 GL error is set if a subrange of the mapping is modified and not flushed, 171 but data within the corresponding subrange of the buffer is undefined. This 172 flag may only be used in conjunction with MAP_WRITE_BIT. When this option 173 is selected, flushing is strictly limited to regions that are explicitly 174 indicated with calls to FlushMappedBufferRange prior to unmap; if this 175 option is not selected UnmapBuffer will automatically flush the entire 176 mapped range when called. 177 178 MAP_UNSYNCHRONIZED_BIT indicates that the GL should not attempt to 179 synchronize pending operations on the buffer prior to returning from 180 MapBufferRange. No GL error is generated if pending operations which source 181 or modify the buffer overlap the mapped region, but the result of such 182 previous and any subsequent operations is undefined. This flag may not be 183 used in combination with MAP_READ_BIT. 184 185 MapBufferRange sets buffer object state values as shown in table 2.mbr. 186 187 Name Value 188 ---- ----- 189 BUFFER_ACCESS Depends on <access>[1] 190 BUFFER_MAPPED TRUE 191 BUFFER_MAP_POINTER pointer to the data store 192 BUFFER_MAP_OFFSET <offset> 193 BUFFER_MAP_LENGTH <length> 194 --------------------------------------------- 195 Table 2.mbr: Buffer object state set by MapBufferRange. 196 [1] BUFFER_ACCESS is set to READ_ONLY, WRITE_ONLY, or READ_WRITE if 197 <access> & (MAP_READ_BIT|MAP_WRITE_BIT) is respectively 198 MAP_READ_BIT, MAP_WRITE_BIT, or MAP_READ_BIT|MAP_WRITE_BIT. 199 200 201 Errors 202 203 If an error occurs, MapBufferRange returns a NULL pointer. 204 205 INVALID_VALUE is generated if <offset> or <length> is negative, or if 206 offset+length is greater than the value of BUFFER_SIZE. 207 208 INVALID_OPERATION is generated for any of the following conditions: 209 210 - The buffer is already in a mapped state. 211 - Neither MAP_READ_BIT nor MAP_WRITE_BIT is set. 212 - MAP_READ_BIT is set and any of MAP_INVALIDATE_RANGE_BIT, 213 MAP_INVALIDATE_BUFFER_BIT, or MAP_UNSYNCHRONIZED_BIT is set. 214 - MAP_FLUSH_EXPLICIT_BIT is set and MAP_WRITE_BIT is not set. 215 216 No GL error is generated if memory outside the mapped range is modified or 217 queried, but the result is undefined and system errors (possibly including 218 program termination) may occur. 219 220 221 If a buffer is mapped with the MAP_FLUSH_EXPLICIT_BIT flag, modifications 222 to the mapped range may be indicated by calling 223 224 void FlushMappedBufferRange( enum target, intptr offset, sizeiptr length ); 225 226 with <target> set to one of ARRAY_BUFFER, ELEMENT_ARRAY_BUFFER, 227 PIXEL_UNPACK_BUFFER, PIXEL_PACK_BUFFER, TEXTURE_BUFFER_EXT, or 228 UNIFORM_BUFFER_EXT, <offset> and <length> indicate a modified subrange of 229 the mapping, in basic machine units. The specified subrange to flush is 230 relative to the start of the currently mapped range of buffer. 231 FlushMappedBufferRange may be called multiple times to indicate distinct 232 subranges of the mapping which require flushing. 233 234 Errors 235 236 INVALID_VALUE is generated if <offset> or <length> is negative, or if 237 <offset>+<length> exceeds the size of the mapping. 238 239 INVALID_OPERATION is generated if buffer is not mapped, or is mapped without 240 the MAP_FLUSH_EXPLICIT_BIT flag. 241 242Additions to Chapter 2 of the OpenGL 2.0 Specification (Buffer Objects) 243 244Errors 245 246 INVALID_ENUM is generated if the <target> parameter of 247 MapBufferRange and FlushMappedBufferRange is not ARRAY_BUFFER, 248 ELEMENT_ARRAY_BUFFER, PIXEL_PACK_BUFFER, PIXEL_UNPACK_BUFFER, 249 TEXTURE_BUFFER_EXT, or UNIFORM_BUFFER_EXT. 250 251 INVALID_OPERATION is generated if FlushMappedBufferRange is executed 252 while zero is bound to the <target> parameter. 253 254 INVALID_OPERATION is generated if FlushMappedBufferRange is called 255 outside the execution of a MapBufferRange and the corresponding execution of 256 UnmapBuffer. 257 258 INVALID_OPERATION may be generated if any of the commands defined in this 259 extension is executed between the execution of Begin and the corresponding 260 execution of End. 261 262New Implementation Dependent State 263 264 None 265 266GLX Protocol 267 268 FlushMappedBufferRange is an entirely client-side command. 269 270 The following new non-rendering command is added: 271 272 MapBufferRange 273 274 1 CARD8 opcode (X assigned) 275 1 205 GLX opcode 276 2 8 request length 277 4 GLX_CONTEXT_TAG context tag 278 8 CARD64 offset 279 8 CARD64 length 280 4 ENUM target 281 4 BITFIELD access 282 => 283 1 1 reply 284 1 unused 285 2 CARD16 sequence number 286 4 0 reply length 287 4 unused 288 4 CARD32 0 on error, otherwise 1. 289 8 CARD64 mapping address 290 8 unused 291 292Usage Examples 293 294 /* bind and initialize a buffer object */ 295 int size = 65536; 296 glBindBufferARB ( 1, GL_ARRAY_BUFFER_ARB ); 297 glBufferDataARB ( GL_ARRAY_BUFFER_ARB, size, NULL, GL_DYNAMIC_DRAW_ARB ); 298 299/* the following are not meant to be executed as a group, since there are no 300 * unmap calls shown here - they are meant to show different combinations of 301 * map options in conjunction with MapBufferRange and FlushMappedBufferRange. 302 */ 303 304 /* Map the entire buffer with read and write 305 * (identical semantics to MapBufferARB) 306 */ 307 void *ptr = glMapBufferRange( GL_ARRAY_BUFFER_ARB, 0, size, MAP_READ_BIT | MAP_WRITE_BIT ); 308 309 /* Map the entire buffer as write only 310 */ 311 void *ptr = glMapBufferRange( GL_ARRAY_BUFFER_ARB, 0, size, MAP_WRITE_BIT ); 312 313 314 /* Map the last 1K bytes of the buffer as write only. 315 */ 316 void *ptr = glMapBufferRange( GL_ARRAY_BUFFER_ARB, size-1024, 1024, MAP_WRITE_BIT ); 317 318 319 /* Map the last 1K bytes of the buffer as write only, and invalidate the range. 320 * locations within that range can assume undefined values. 321 * locations written while mapped take on new values as expected. 322 * no changes occur outside the range mapped. 323 */ 324 void *ptr = glMapBufferRange( GL_ARRAY_BUFFER_ARB, size-1024, 1024, MAP_WRITE_BIT | MAP_INVALIDATE_RANGE_BIT ); 325 326 327 /* Map the first 1K bytes of the buffer as write only, and invalidate the entire buffer. 328 * all locations within the buffer can assume undefined values. 329 * locations written while mapped take on new values as expected. 330 */ 331 void *ptr = glMapBufferRange( GL_ARRAY_BUFFER_ARB, 0, 1024, MAP_WRITE_BIT | MAP_INVALIDATE_BUFFER_BIT ); 332 333 334 /* Map the first 32K bytes of the buffer as write only, and invalidate that range. 335 * Indicate that we will explicitly inform GL which ranges are actually written. 336 * Locations within that range can assume undefined values. 337 * Only the locations which are written and subsequently flushed are guaranteed 338 * to take on defined values. 339 * Write data to the first 8KB of the range, then flush it. 340 * Write data to the last 8KB of the range, then flush it. 341 */ 342 void *ptr = glMapBufferRange( GL_ARRAY_BUFFER_ARB, 0, 32768, MAP_WRITE_BIT | MAP_INVALIDATE_RANGE_BIT | MAP_FLUSH_EXPLICIT_BIT ); 343 344 memset( ptr, 0x00, 8192 ); /* write zeroes to first 8KB of range */ 345 FlushMappedBufferRange( GL_ARRAY_BUFFER_ARB, 0, 8192 ); 346 347 memset( ((char*)ptr)+24576, 0xFF, 8192 ); /* write FF's to last 8KB of range */ 348 FlushMappedBufferRange( GL_ARRAY_BUFFER_ARB, 24576, 8192 ); 349 350 351 /* Map the entire buffer for write - unsynchronized. 352 * GL will not block for prior operations to complete. Application must 353 * use other synchronization techniques to ensure correct operation. 354 */ 355 void *ptr = glMapBufferRange( GL_ARRAY_BUFFER_ARB, 0, size, MAP_WRITE_BIT | MAP_UNSYNCHRONIZED_BIT); 356 357 358Revision History 359 360 Rev. Date Author Changes 361 ---- ---------- -------- ---------------------------------------------- 362 1 06/03/2008 rcb Initial version with sample code. 363 2 07/07/2008 rcb Various edits to match GL3 core spec. 364 3 08/07/2008 jleech Remove ARB suffixes. 365 4 01/24/2011 srahman Add GLX protocol. 366 5 06/22/2012 jleech Define how buffer object state is affected 367 by MapBufferRange. 368