EXT_external_objects_fd
简述
从fd导入texture特别有用。 fd导入后就不能再操作了，这个函数有ownership转移意味。
顺序是：fd -> memory object -> texture
方法：
void importFdAsTexture(int fd, int size, GLuint tex, int w, int h) {
GLuint tex;
glGenTextures(1, &tex);
// create memObj and import fd as memObj
GLuint memObj = 0;
glCreateMemoryObjectsEXT(1, &memObj);
GLint param = GL_TRUE;
glMemoryObjectParameterivEXT(memObj, GL_DEDICATED_MEMORY_OBJECT_EXT, ¶m);
glImportMemoryFdEXT(memObj, size, GL_HANDLE_TYPE_OPAQUE_FD_EXT, fd);
// make memOjb texture's storage
glTextureStorageMem2DEXT(tex, 1, (GLuint)GL_RGBA8, w, h, memObj, 0);
return tex;
}
上述代码中，fd和size是要导入的fd和它内容的大小，w, h是要导入为的texture的name和宽高。
用到的几个函数的介绍
glCreateMemoryObjectsEXT
所属扩展：EXT_external_objects
原型：
void glCreateMemoryObjectsEXT(sizei n,
uint *memoryObjects);
语法跟glGenTextures类似.
glMemoryObjectParameterivEXT
所属扩展：EXT_external_objects
原型：
void glMemoryObjectParameterivEXT(uint memoryObject,
enum pname,
const int *params);
语法跟glTexParameteri类似。
pname可取的值为：
DEDICATED_MEMORY_OBJECT_EXT 0x9581
[[ The following are available when GL_EXT_protected_textures is available ]]
PROTECTED_MEMORY_OBJECT_EXT 0x959B
可取的值：
| Name | Legal Values |
+-----------------------------+--------------+
| DEDICATED_MEMORY_OBJECT_EXT | FALSE, TRUE |
| PROTECTED_MEMORY_OBJECT_EXT | FALSE, TRUE |
+-----------------------------+--------------+
glImportMemoryFdEXT
原型：
void ImportMemoryFdEXT(uint memory,
uint64 size,
enum handleType,
int fd);
其为memory为memObj的name，即glCreateMemoryObjectsEXT的出参。
handleType目前可取值只有HANDLE_TYPE_OPAQUE_FD_EXT。
size的单位是字节,byte。
glTextureStorageMem2DEXT
所属扩展:EXT_external_objects
原型：
void TextureStorageMem2DEXT(uint texture,
sizei levels,
enum internalFormat,
sizei width,
sizei height,
uint memory,
uint64 offset);
texture和memory分别为texture和memobj的name。 levels是说导入的纹理有几个mipmap level。 offset是说在memobj中的偏移，正常为0。 internalFormat为纹理的内部格式。
正文
Name
EXT_external_objects_fd
Name Strings
GL_EXT_memory_object_fd
GL_EXT_semaphore_fd
Contributors
Carsten Rohde, NVIDIA
James Jones, NVIDIA
Jan-Harald Fredriksen, ARM
Jeff Juliano, NVIDIA
Contact
James Jones, NVIDIA (jajones 'at' nvidia.com)
Status
Complete
Version
Last Modified Date: June 2, 2017
Revision: 7
Number
504
OpenGL ES Extension #281
Dependencies
Written against the OpenGL 4.5 and OpenGL ES 3.2 specifications
GL_EXT_memory_object_fd requires GL_EXT_memory_object
GL_EXT_semaphore_fd requires GL_EXT_semaphore
Requires ARB_texture_storage or a version of OpenGL or OpenGL ES that
incorporates it.
Overview
Building upon the OpenGL memory object and semaphore framework
defined in EXT_external_objects, **this extension enables an OpenGL
application to import a memory object or semaphore from POSIX file
descriptor external handles**.
New Procedures and Functions
If the GL_EXT_memory_object_fd string is reported, the following
commands are added:
void ImportMemoryFdEXT(uint memory,
uint64 size,
enum handleType,
int fd);
If the GL_EXT_semaphore_fd string is reported, the following commands
are added:
void ImportSemaphoreFdEXT(uint semaphore,
enum handleType,
int fd);
New Tokens
The following tokens are added if either of the GL_EXT_memory_object_fd
or GL_EXT_semaphore_fd strings are reported:
Accepted by the <handleType> parameter of ImportMemoryFdEXT() or
ImportSemaphoreFdEXT().
HANDLE_TYPE_OPAQUE_FD_EXT 0x9586
Additions to Chapter 4 of the OpenGL 4.5 Specification (Event Model)
Add the following entry to table 4.2 "Commands for importing
external semaphore handles."
| Handle Type | Import command |
+---------------------------+----------------------+
| HANDLE_TYPE_OPAQUE_FD_EXT | ImportSemaphoreFdEXT |
+---------------------------+----------------------+
Replace the paragraph in section 4.2.1 beginning "External handles
are often defined..." with the following
The command
ImportSemaphoreFdEXT(uint semaphore,
enum handleType,
int fd);
imports a semaphore from the file descriptor <fd>. What type of
object <fd> refers to is determined by <handleType>. A successful
import operation transfers ownership of <fd> to the GL
implementation, and performing any operation on <fd> in the
application after an import results in undefined behavior.
Additions to Chapter 6 of the OpenGL 4.5 Specification (Memory Objects)
Add the following entry to table 6.2 "Commands for importing
external memory handles."
| Handle Type | Import command |
+---------------------------+-------------------+
| HANDLE_TYPE_OPAQUE_FD_EXT | ImportMemoryFdEXT |
+---------------------------+-------------------+
Replace the paragraph in section 6.1 beginning "External handles are
often defined..." with the following
The command
void ImportMemoryFdEXT(uint memory,
uint64 size,
enum handleType,
int fd);
imports a memory object of length <size> from the file descriptor
<fd>. What type of object <fd> refers to is determined by
<handleType>. A successful import operation transfers ownership
of <fd> to the GL implementation, and performing any operation on
<fd> in the application after an import results in undefined
behavior.
Issues
1) Does this extension need to support importing Android/Linux
sync FD handles?
RESOLVED: No. These are already usable in GL via extensions to the
EGLSync mechanism. Adding them here in order to support them in GLX
contexts is not compelling enough to justify the additional effort.
Revision History
Revision 7, 2017-06-02 (James Jones)
- Added extension numbers.
- Clarified which extensions each command and token belongs to.
- Marked complete.
Revision 6, 2017-05-24 (James Jones)
- Filled in real token values
Revision 5, 2017-04-04 (James Jones)
- Clarified the effects of import operations on file descriptors.
Revision 4, 2017-03-17 (James Jones)
- Renamed from KHR to EXT.
Revision 3, 2016-09-28 (James Jones)
- Merged GL_EXT_memory_object_fd and GL_EXT_semaphore_fd.
- Added spec body describing the new commands and tokens.
- Added issue 1.
Revision 2, 2016-08-15 (Jeff Juliano)
- Clarified overview text.
Revision 1, 2016-08-05 (James Jones)
- Initial draft.