Name EXT_map_buffer_range Name Strings GL_EXT_map_buffer_range Contributors Contributors to ARB_map_buffer_range desktop OpenGL extension from which this extension borrows heavily Contact Benj Lipchak (lipchak 'at' apple 'dot' com) Status Complete Version Last Modified Date: August 21, 2014 Author Revision: 4 Number OpenGL ES Extension #121 Dependencies OpenGL ES 1.1 or OpenGL ES 2.0 is required. OES_mapbuffer is required. This specification is written against the OpenGL ES 2.0.25 specification. Overview EXT_map_buffer_range expands the buffer object API to allow greater performance when a client application only needs to write to a sub-range of a buffer object. To that end, this extension introduces two new buffer object features: non-serialized buffer modification and explicit sub-range flushing for mapped buffer objects. OpenGL requires that commands occur in a FIFO manner meaning that any changes to buffer objects either block until the data has been processed by the OpenGL pipeline or else create extra copies to avoid such a block. By providing a method to asynchronously modify buffer object data, an application is then able to manage the synchronization points themselves and modify ranges of data contained by a buffer object even though OpenGL might still be using other parts of it. This extension also provides a method for explicitly flushing ranges of a mapped buffer object so OpenGL does not have to assume that the entire range may have been modified. Further, it allows the application to more precisely specify its intent with respect to reading, writing, and whether the previous contents of a mapped range of interest need be preserved prior to modification. New Procedures and Functions void *MapBufferRangeEXT(enum target, intptr offset, sizeiptr length, bitfield access); void FlushMappedBufferRangeEXT(enum target, intptr offset, sizeiptr length); New Tokens Accepted by the parameter of MapBufferRangeEXT: MAP_READ_BIT_EXT 0x0001 MAP_WRITE_BIT_EXT 0x0002 MAP_INVALIDATE_RANGE_BIT_EXT 0x0004 MAP_INVALIDATE_BUFFER_BIT_EXT 0x0008 MAP_FLUSH_EXPLICIT_BIT_EXT 0x0010 MAP_UNSYNCHRONIZED_BIT_EXT 0x0020 Additions to Chapter 2 of the OpenGL ES 2.0 Specification (OpenGL ES Operation) Add to the end of Section 2.9 "Buffer Objects" (p. 24): All or part of the data store of a buffer object may be mapped into the client's address space by calling void *MapBufferRangeEXT(enum target, intptr offset, sizeiptr length, bitfield access); with set to ARRAY_BUFFER or ELEMENT_ARRAY_BUFFER. and indicate the range of data in the buffer object that is to be mapped, in terms of basic machine units. is a bitfield containing flags which describe the requested mapping. These flags are described below. If no error occurs, a pointer to the beginning of the mapped range is returned once all pending operations on that buffer have completed, and may be used to modify and/or query the corresponding range of the buffer, according to the following flag bits set in : * MAP_READ_BIT_EXT indicates that the returned pointer may be used to read buffer object data. No GL error is generated if the pointer is used to query a mapping which excludes this flag, but the result is undefined and system errors (possibly including program termination) may occur. * MAP_WRITE_BIT_EXT indicates that the returned pointer may be used to modify buffer object data. No GL error is generated if the pointer is used to modify a mapping which excludes this flag, but the result is undefined and system errors (possibly including program termination) may occur. Pointer values returned by MapBufferRangeEXT 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. 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 BUFFER_USAGE and . Using a mapping in a fashion inconsistent with these values is liable to be multiple orders of magnitude slower than using normal memory. The following optional flag bits in may be used to modify the mapping: * MAP_INVALIDATE_RANGE_BIT_EXT indicates that the previous contents of the specified range may be discarded. Data within this range are undefined with the exception of subsequently written data. No GL error is generated if subsequent GL operations access unwritten data, but the result is undefined and system errors (possibly including program termination) may occur. This flag may not be used in combination with MAP_READ_BIT_EXT. * MAP_INVALIDATE_BUFFER_BIT_EXT indicates that the previous contents of the entire buffer may be discarded. Data within the entire buffer are undefined with the exception of subsequently written data. No GL error is generated if subsequent GL operations access unwritten data, but the result is undefined and system errors (possibly including program termination) may occur. This flag may not be used in combination with MAP_READ_BIT_EXT. * MAP_FLUSH_EXPLICIT_BIT_EXT indicates that one or more discrete subranges of the mapping may be modified. When this flag is set, modifications to each subrange must be explicitly flushed by calling FlushMappedBufferRangeEXT. No GL error is set if a subrange of the mapping is modified and not flushed, but data within the corresponding subrange of the buffer is undefined. This flag may only be used in conjunction with MAP_WRITE_BIT_EXT. When this option is selected, flushing is strictly limited to regions that are explicitly indicated with calls to FlushMappedBufferRangeEXT prior to unmap; if this option is not selected UnmapBufferOES will automatically flush the entire mapped range when called. * MAP_UNSYNCHRONIZED_BIT_EXT indicates that the GL should not attempt to synchronize pending operations on the buffer prior to returning from MapBufferRangeEXT. No GL error is generated if pending operations which source or modify the buffer overlap the mapped region, but the result of such previous and any subsequent operations is undefined. A successful MapBufferRangeEXT sets buffer object state values as shown in table 2.mbr. Name Value ------------------- ----- BUFFER_ACCESS_FLAGS BUFFER_MAPPED TRUE BUFFER_MAP_POINTER pointer to the data store BUFFER_MAP_OFFSET BUFFER_MAP_LENGTH Table 2.mbr: Buffer object state set by MapBufferRangeEXT. If an error occurs, MapBufferRangeEXT returns a NULL pointer. An INVALID_VALUE error is generated if or is negative, if + is greater than the value of BUFFER_SIZE, or if has any bits set other than those defined above. An INVALID_OPERATION error is generated for any of the following conditions: * is zero. * The buffer is already in a mapped state. * Neither MAP_READ_BIT_EXT nor MAP_WRITE_BIT_EXT is set. * MAP_READ_BIT_EXT is set and any of MAP_INVALIDATE_RANGE_BIT_EXT, MAP_INVALIDATE_BUFFER_BIT_EXT, or MAP_UNSYNCHRONIZED_BIT_EXT is set. * MAP_FLUSH_EXPLICIT_BIT_EXT is set and MAP_WRITE_BIT_EXT is not set. An OUT_OF_MEMORY error is generated if MapBufferRangeEXT fails because memory for the mapping could not be obtained. No error is generated if memory outside the mapped range is modified or queried, but the result is undefined and system errors (possibly including program termination) may occur. If a buffer is mapped with the MAP_FLUSH_EXPLICIT_BIT_EXT flag, modifications to the mapped range may be indicated by calling void FlushMappedBufferRangeEXT(enum target, intptr offset, sizeiptr length); with set to ARRAY_BUFFER or ELEMENT_ARRAY_BUFFER. and indicate a modified subrange of the mapping, in basic machine units. The specified subrange to flush is relative to the start of the currently mapped range of buffer. FlushMappedBufferRangeEXT may be called multiple times to indicate distinct subranges of the mapping which require flushing. An INVALID_VALUE error is generated if or is negative, or if + exceeds the size of the mapping. An INVALID_OPERATION error is generated if zero is bound to . An INVALID_OPERATION error is generated if the buffer bound to is not mapped, or is mapped without the MAP_FLUSH_EXPLICIT_BIT_EXT flag. New Implementation Dependent State None Usage Examples /* bind and initialize a buffer object */ int size = 65536; glBindBuffer(GL_ARRAY_BUFFER, 1); glBufferData(GL_ARRAY_BUFFER, size, NULL, GL_DYNAMIC_DRAW); /* the following are not meant to be executed as a group, since there are no * unmap calls shown here - they are meant to show different combinations of * map options in conjunction with MapBufferRangeEXT and * FlushMappedBufferRangeEXT. */ /* Map the entire buffer with read and write * (identical semantics to MapBufferOES). */ void *ptr = glMapBufferRangeEXT(GL_ARRAY_BUFFER, 0, size, MAP_READ_BIT_EXT | MAP_WRITE_BIT_EXT); /* Map the entire buffer as write only. */ void *ptr = glMapBufferRangeEXT(GL_ARRAY_BUFFER, 0, size, MAP_WRITE_BIT_EXT); /* Map the last 1K bytes of the buffer as write only. */ void *ptr = glMapBufferRangeEXT(GL_ARRAY_BUFFER, size-1024, 1024, MAP_WRITE_BIT_EXT); /* Map the last 1K bytes of the buffer as write only, and invalidate the * range. Locations within that range can assume undefined values. * Locations written while mapped take on new values as expected. * No changes occur outside the range mapped. */ void *ptr = glMapBufferRangeEXT(GL_ARRAY_BUFFER, size-1024, 1024, MAP_WRITE_BIT_EXT | MAP_INVALIDATE_RANGE_BIT_EXT); /* Map the first 1K bytes of the buffer as write only, and invalidate the * entire buffer. All locations within the buffer can assume undefined * values. Locations written while mapped take on new values as expected. */ void *ptr = glMapBufferRangeEXT(GL_ARRAY_BUFFER, 0, 1024, MAP_WRITE_BIT_EXT | MAP_INVALIDATE_BUFFER_BIT_EXT); /* Map the first 32K bytes of the buffer as write only, and invalidate * that range. Indicate that we will explicitly inform GL which ranges are * actually written. Locations within that range can assume undefined * values. Only the locations which are written and subsequently flushed * are guaranteed to take on defined values. * Write data to the first 8KB of the range, then flush it. * Write data to the last 8KB of the range, then flush it. */ void *ptr = glMapBufferRangeEXT(GL_ARRAY_BUFFER, 0, 32768, MAP_WRITE_BIT_EXT | MAP_INVALIDATE_RANGE_BIT_EXT | MAP_FLUSH_EXPLICIT_BIT_EXT); memset(ptr, 0x00, 8192); /* write zeroes to first 8KB of range */ glFlushMappedBufferRangeEXT(GL_ARRAY_BUFFER, 0, 8192); memset(((char*)ptr)+24576, 0xFF, 8192);/* write FFs to last 8KB of range */ glFlushMappedBufferRangeEXT(GL_ARRAY_BUFFER, 24576, 8192); /* Map the entire buffer for write - unsynchronized. * GL will not block for prior operations to complete. Application must * use other synchronization techniques to ensure correct operation. */ void *ptr = glMapBufferRangeEXT(GL_ARRAY_BUFFER, 0, size, MAP_WRITE_BIT_EXT | MAP_UNSYNCHRONIZED_BIT_EXT); Revision History Version 4, 2014/08/21 - Fix typo OES_map_buffer -> OES_mapbuffer. Version 3, 2012/06/21 - Recast from APPLE to multivendor EXT Version 2, 2012/06/18 - Correct spec to indicate ES 1.1 may also be okay. Version 1, 2012/06/01 - Conversion from ARB_map_buffer_range to APPLE_map_buffer_range for ES.