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Test Your Knowledge in Computers #439
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A graphics processing unit (GPU) is a specialized electronic circuit designed to rapidly manipulate and alter memory to accelerate the creation of images in a frame buffer intended for output to a display device.
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glxisdirect(3) [redhat man page]

GLXISDIRECT()															     GLXISDIRECT()

glXIsDirect - indicate whether direct rendering is enabled C SPECIFICATION
Bool glXIsDirect( Display *dpy, GLXContext ctx ) delim $$ PARAMETERS
dpy Specifies the connection to the X server. ctx Specifies the GLX context that is being queried. DESCRIPTION
glXIsDirect returns True if ctx is a direct rendering context, False otherwise. Direct rendering contexts pass rendering commands directly from the calling process's address space to the rendering system, bypassing the X server. Nondirect rendering contexts pass all rendering commands to the X server. ERRORS
GLXBadContext is generated if ctx is not a valid GLX context. SEE ALSO
glXCreateContext GLXISDIRECT()

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glXCreateContext - create a new GLX rendering context C SPECIFICATION
GLXContext glXCreateContext( Display *dpy, XVisualInfo *vis, GLXContext shareList, Bool direct ) delim $$ PARAMETERS
dpy Specifies the connection to the X server. vis Specifies the visual that defines the frame buffer resources available to the rendering context. It is a pointer to an XVisual- Info structure, not a visual ID or a pointer to a Visual. shareList Specifies the context with which to share display lists. NULL indicates that no sharing is to take place. direct Specifies whether rendering is to be done with a direct connection to the graphics system if possible (True) or through the X server (False). DESCRIPTION
glXCreateContext creates a GLX rendering context and returns its handle. This context can be used to render into both windows and GLX pixmaps. If glXCreateContext fails to create a rendering context, NULL is returned. If direct is True, then a direct rendering context is created if the implementation supports direct rendering, if the connection is to an X server that is local, and if a direct rendering context is available. (An implementation may return an indirect context when direct is True). If direct is False, then a rendering context that renders through the X server is always created. Direct rendering provides a per- formance advantage in some implementations. However, direct rendering contexts cannot be shared outside a single process, and they may be unable to render to GLX pixmaps. If shareList is not NULL, then all display-list indexes and definitions are shared by context shareList and by the newly created context. An arbitrary number of contexts can share a single display-list space. However, all rendering contexts that share a single display-list space must themselves exist in the same address space. Two rendering contexts share an address space if both are nondirect using the same server, or if both are direct and owned by a single process. Note that in the nondirect case, it is not necessary for the calling threads to share an address space, only for their related rendering contexts to share an address space. If the GL version is 1.1 or greater, then all texture objects except object 0, are shared by any contexts that share display lists. NOTES
XVisualInfo is defined in Xutil.h. It is a structure that includes visual, visualID, screen, and depth elements. A process is a single execution environment, implemented in a single address space, consisting of one or more threads. A thread is one of a set of subprocesses that share a single address space, but maintain separate program counters, stack spaces, and other related global data. A thread that is the only member of its subprocess group is equivalent to a process. It may not be possible to render to a GLX pixmap with a direct rendering context. ERRORS
NULL is returned if execution fails on the client side. BadMatch is generated if the context to be created would not share the address space or the screen of the context specified by shareList. BadValue is generated if vis is not a valid visual (for example, if a particular GLX implementation does not support it). GLXBadContext is generated if shareList is not a GLX context and is not NULL. BadAlloc is generated if the server does not have enough resources to allocate the new context. SEE ALSO
glXDestroyContext, glXGetConfig, glXIsDirect, glXMakeCurrent GLXCREATECONTEXT()

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