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Name
VMWX_map_buffer_debug
Name Strings
GL_VMWX_map_buffer_debug
Contact
Jose Fonseca, VMware (jfonseca 'at' vmware.com)
IP Status
No known IP claims.
Status
Implemented by Apitrace
Version
Last Modified Date: December 14, 2014
Version: 1
Number
TBD.
Dependencies
GL_ARB_buffer_storage is required.
Overview
This extension provides a mechanism for the application to notify OpenGL
debugging tools that it modified ranges of persistent buffer mappings,
without explicitly flushing buffer ranges.
New Procedures and Functions
void NotifyMappedBufferRangeVMWX(const void * start, sizeiptr length);
New Tokens
Accepted in the <flags> parameter of BufferStorage:
MAP_NOTIFY_EXPLICIT_BIT_VMWX 0x80000000
Accepted as part of the <access> parameter to MapBufferRange and
MapNamedBufferRange:
MAP_NOTIFY_EXPLICIT_BIT_VMWX 0x80000000
Additions to Chapter 6 of the OpenGL Core Profile Specification, Version 4.3,
"Buffer Objects"
Modify Section 6.2, "Creating and Modifying Buffer Object Data Stores"
Add to the bulleted list describing flags that modify buffer storage
flags, p.57.
* MAP_NOTIFY_EXPLICIT_BIT_VMWX indicates that the application will
notify whenever discrete subranges of coherent mappings are
notified.
This flag may only be used in conjunction with MAP_PERSISTENT_BIT.
Modify Section 6.3, "Mapping and Unmapping Buffer Data"
Add to the bulleted list describing flags that modify buffer mappings,
p.62.
* MAP_NOTIFY_EXPLICIT_BIT_VMWX indicates that discrete subranges of the
mapping will be notified explicitly when modified.
When this flag is set, modifications to each subrange must be
explicitly flushed by calling NotifyMappedBufferRangeVMWX.
This flag may only be used in conjunction with MAP_PERSISTENT_BIT.
If this bit is set, the value of BUFFER_STORAGE_FLAGS for the buffer
being mapped must include MAP_NOTIFY_EXPLICIT_BIT_VMWX.
Issues
1) Why is this extension necessary?
It is true that an application may be friendly towards OpenGL debugging
tools that intercept calls by ensuring that MAP_PERSISTENT_BIT is always
set with MAP_FLUSH_EXPLICIT_BIT, and never with MAP_COHERENT_BIT. But
this restricts/deviates from intended behavior. This extensions provides
a mechanism for applications to notify debugging tools without affecting
behavior.
2) Why the new MAP_NOTIFY_EXPLICIT_BIT_VMWX token?
To be future-proof.
In order to record complete traces, OpenGL tracing tools may choose to
mask out support for coherent mappings by failing BufferStorage calls with
OUT_OF_MEMORY when MAP_COHERENT_BIT is set without
MAP_NOTIFY_EXPLICIT_BIT_VMWX; or use techniques to approximately detect
writes to coherent mappings if the application calls MapBufferRange with
MAP_COHERENT_BIT and MAP_NOTIFY_EXPLICIT_BIT_VMWX.
It is therefore crucial that applications that want to explicitily notify
modified subranges with calls NotifyMappedBufferRangeVMWX set the
MAP_NOTIFY_EXPLICIT_BIT_VMWX bit both on BufferStorage and MapBufferRange
calls, to opt-out of further interference from debugging tools.
Revision History
Version 1, 2014/12/14 - Initial version
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