Name
EXT_import_context
Name Strings
GLX_EXT_import_context
Version
$Date: 1995/10/06 00:47:06 $ $Revision: 1.14 $
Number
47
Dependencies
This extension affects the definition of SGIX_FBConfig.
Overview
This extension allows multiple X clients to share an indirect
rendering context.
Additional convenience procedures to get the current Display*
bound to a context as well as other context information are
also added.
Issues
Does glXImportGLXContext also need to take an XVisualInfo*?
No. This information will be retrieved from the server.
New Procedures and Functions
Display *glXGetCurrentDisplayEXT();
int glXQueryContextInfoEXT(Display *dpy, GLXContext context,
int attribute,int *value);
GLXContextID glXGetContextIDEXT(const GLXContext context);
GLXContext glXImportContextEXT(Display *dpy, GLXContextID contextID);
void glXFreeContextEXT(Display *dpy, GLXContext context);
New Tokens
Accepted by the <attribute> parameter of glXQueryContextInfoEXT:
GLX_SHARE_CONTEXT_EXT 0x800A
GLX_VISUAL_ID_EXT 0x800B
GLX_SCREEN_EXT 0x800C
Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation)
None
Additions to Chapter 3 of the 1.0 Specification (Rasterization)
None
Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations
and the Frame Buffer)
None
Additions to Chapter 5 of the 1.0 Specification (Special Functions)
None
Additions to Chapter 6 of the 1.0 Specification (State and State Requests)
None
Additions to the GLX Specification
[Add the following to Section 3.2.4 of the GLX Specification
(Rendering Contexts)]
To get the display associated with the current context, use
Display *glXGetCurrentDisplayEXT();
If there is no current context, NULL is returned. No round trip
is forced to the server; unlike most X calls that return a value,
glXGetCurrentDisplayEXT does not flush any pending events.
To obtain the value of a context's attribute, use
int glXQueryContextInfoEXT(Display *dpy, GLXContext context,
int attribute, int *value);
glxQueryContextInfoEXT returns through <value> the value of
<attribute> for <context>. It may cause a round trip to the
server.
The values and types corresponding to each GLX context attribute
are listed in the table below.
GLX context attribute type context information
--------------------- ---- -------------------
GLX_SHARE_CONTEXT_EXT XID xid of the share list context
GLX_VISUAL_ID_EXT XID visual id
GLX_SCREEN_EXT int screen number
glxQueryContextInfoEXT returns GLX_BAD_ATTRIBUTE if <attribute>
is not a valid GLX context attribute or GLX_BAD_CONTEXT if <context>
is invalid, otherwise it returns Success.
To obtain the XID of a GLXContext, use
GLXContextID glXGetContextIDEXT(const GLXContext context);
No round trip is forced to the server; unlike most X calls that
return a value, glXGetContextIDEXT does not flush any
pending events.
To create a GLXContext given the XID of an existing GLXContext, use
GLXContext glXImportContextEXT(Display *dpy,
GLXContextID contextID);
glXImportContextEXT may be used in place of glXCreateContext to
share another process's indirect rendering context.
Only the server-side context information can be shared between
X clients; client-side state, such as pixel storage modes,
cannot be shared. Thus, glXImportContextEXT, must allocate
memory to store client-side information. This memory is freed
by calling glXFreeContextEXT.
This call does not create a new XID. It merely makes an
existing object available to the importing client (Display *).
Like any XID, it goes away when the creating client drops its
connection or the ID is explicitly deleted. Note that this is
when the XID goes away. The object goes away when the XID
goes away AND the context is not current to any thread.
If <contextID> does not refer to a valid context, then
a BadContext error is generated; if <contextID> refers to
direct rendering context then no error is generated but
glXImportContextEXT returns NULL.
To free the client-side part of a GLXContext that was created
with glXImportContext, use
void glXFreeContextEXT(Display *dpy, GLXContext context);
glXFreeContext does not free the server-side context information
or the XID associated with the server-side context.
[Add the following clarification to glXMakeCurrent]
Change:
If <context> is current to some other thread, then glXMakeCurrent
will generate a BadAccess error.
To:
If <context> is current to some other thread or process, then
glXMakeCurrent will generate a BadAccess error.
GLX Protocol
One new GLX protocol command is added.
QueryContextInfo
1 CARD8 opcode (X assigned)
1 17 GLX opcode (glXVendorPrivateWithReply)
2 4 request length
4 15 vendor specific opcode
4 unused corresponds to context tag in header
4 GLX_CONTEXT context id
=>
1 1 Reply
1 unused
2 CARD16 sequence number
4 2*n reply length
4 CARD32 n
20 unused
8*n LISTofCARD32 attribute, value pairs
Errors
None
New State
None
New Implementation Dependent State
None