GLX_EXT_import_context

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

Implementation Support

   List of OpenGL implementations supporting the GLX_EXT_import_context extension

Original File

   Original text file for the GLX_EXT_import_context extension