OVERVIEW
OpenGL (called GL in other pages) is a high-performance 3D-oriented
renderer. It is available in the X window system through the GLX
extension. To determine whether the GLX extension is supported by an X
server, and if so, what version is supported, call glXQueryExtension
and glXQueryVersion.
GLX extended X servers make a subset of their visuals available for
OpenGL rendering. Drawables created with these visual can also be ren-
dered into using the core X renderer and or any other X extension that
is compatible with all core X visuals.
GLX extends a drawable's standard color buffer with additional buffers.
These buffers include back and auxiliary color buffers, a depth buffer,
a stencil buffer, and a color accumulation buffer. Some or all of the
buffers listed are included in each X visual that supports OpenGL.
GLX supports rendering into three types of drawables: windows, pixmaps
and pbuffers (pixel buffers). GLX windows and pixmaps are X resources,
and capable of accepting core X rendering as well as OpenGL rendering.
GLX pbuffers are GLX only resources, and might not accept core X ren-
dering.
To render using OpenGL into a GLX drawable, you must determine the
appropriate GLXFBConfig which supports the rendering features your
application requires. glXChooseFBConfig returns a GLXFBConfig matching
the required attributes, or NULL if no match is found. A complete list
of GLXFBConfigs supported by a server can be obtained by calling
glXGetFBConfigs. Attributes of a particular GLXFBConfig can be queried
by calling glXGetFBConfigAttrib.
For GLX windows and pixmaps, a suitable X drawable (using either XCre-
ateWindow or XCreatePixmap, respectively) with a matching visual must
be created first. Call glXGetVisualFromFBConfig to obtain the neces-
sary XVisualInfo structure for creating the X drawable. For pbuffers,
no underlying X drawable is required.
To create a GLX window from an X window, call glXCreateWindow. Like-
wise, to create a GLX pixmap, call glXCreatePixmap. Pbuffers are cre-
ated by calling glXCreatePbuffer. Use glXDestroyWindow,
glXDestroyPixmap, and glXDestroyPbuffer to release previously allocated
resources.
A GLX context is required to bind OpenGL rendering to a GLX resource.
A GLX resource and rendering context must have compatible GLXFBConfigs.
To create a GLX context, call glXCreateNewContext. A context may be
bound to a GLX drawable by using glXMakeContextCurrent. This con-
text/drawable pair becomes the current context and current drawable,
and is used by all OpenGL rendering commands until
glXMakeContextCurrent is called with different arguments.
int singleBufferAttributess[] = {
GLX_DRAWABLE_TYPE, GLX_WINDOW_BIT,
GLX_RENDER_TYPE, GLX_RGBA_BIT,
GLX_RED_SIZE, 1, /* Request a single buffered color buffer
*/
GLX_GREEN_SIZE, 1, /* with the maximum number of color bits
*/
GLX_BLUE_SIZE, 1, /* for each component
*/
None };
int doubleBufferAttributes[] = {
GLX_DRAWABLE_TYPE, GLX_WINDOW_BIT,
GLX_RENDER_TYPE, GLX_RGBA_BIT,
GLX_DOUBLEBUFFER, True, /* Request a double-buffered color buffer
with */
GLX_RED_SIZE, 1, /* the maximum number of bits per compo-
nent */
GLX_GREEN_SIZE, 1,
GLX_BLUE_SIZE, 1,
None };
static Bool WaitForNotify( Display *dpy, XEvent *event, XPointer arg )
{
return (event->type == MapNotify) && (event->xmap.window == (Win-
dow) arg); }
XEvent event;
XVisualInfo *vInfo;
XSetWindowAttributes swa;
GLXFBConfig *fbConfigs;
GLXContext context;
GLXWindow glxWin;
int swaMask;
int numReturned;
int swapFlag = True;
/* Open a connection to the X server */
dpy = XOpenDisplay( NULL );
if ( dpy == NULL ) {
printf( "Unable to open a connection to the X server0 );
exit( EXIT_FAILURE );
}
/* Request a suitable framebuffer configuration - try for a double
** buffered configuration first */
fbConfigs = glXChooseFBConfig( dpy, DefaultScreen(dpy),
doubleBufferAttributes, &numReturned
);
if ( fbConfigs == NULL ) { /* no double buffered configs available
*/
fbConfigs = glXChooseFBConfig( dpy, DefaultScreen(dpy),
singleBufferAttributess, &numRe-
turned );
swapFlag = False;
}
/* Create an X colormap and window with a visual matching the first
** returned framebuffer config */
vInfo = glXGetVisualFromFBConfig( dpy, fbConfigs[0] );
swa.border_pixel = 0;
swa.event_mask = StructureNotifyMask;
swa.colormap = XCreateColormap( dpy, RootWindow(dpy,
vInfo->screen),
vInfo->visual, AllocNone );
swaMask = CWBorderPixel | CWColormap | CWEventMask;
xWin = XCreateWindow( dpy, RootWindow(dpy, vInfo->screen), 0, 0,
256, 256,
0, vInfo->depth, InputOutput, vInfo->visual,
swaMask, &swa );
/* Create a GLX context for OpenGL rendering */
context = glXCreateNewContext( dpy, fbConfigs[0], GLX_RGBA_TYPE,
NULL, True );
glFlush();
if ( swapFlag )
glXSwapBuffers( dpy, glxWin );
sleep( 10 );
exit( EXIT_SUCCESS ); }
NOTES
An X color map must be created and passed to XCreateWindow.
A GLX context must be created and bound to a GLX drawable before OpenGL
commands can be executed. OpenGL commands executed while no con-
text/drawable pair is current result in undefined behavior.
Exposure events indicate that all buffers associated with the specified
window may be damaged and should be repainted. Although certain buffers
of some visuals on some systems may never require repainting (the depth
buffer, for example), it is incorrect to write a program assuming that
these buffers will not be damaged.
GLX commands utilize XVisualInfo structures rather than pointers to
visuals or visualIDs directly. XVisualInfo structures contain visual,
visualID, screen, and depth elements, as well as other X-specific
information.
USING GLX EXTENSIONS
All supported GLX extensions will have a corresponding definition in
glx.h and a token in the extension string returned by
glXQueryExtensionsString. For example, if the EXT_visual_info exten-
sion is supported, then this token will be defined in glx.h and
EXT_visual_info will appear in the extension string returned by
glXQueryExtensionsString. The definitions in glx.h can be used at com-
pile time to determine if procedure calls corresponding to an extension
exist in the library.
OpenGL itself is capable of being extended. Refer to glIntro for more
information.
GLX 1.1, GLX 1.2, and GLX 1.3
GLX 1.3 is now supported, and is backward compatible with GLX 1.1 and
GLX 1.2. It introduces new functionality (namely GLXFBConfigs) that
supersedes the GLX 1.2 functionality. GLX 1.2 commands are supported,
but their use in new application development is not recommended.
GLX 1.3 corresponds to OpenGL versions 1.2, and introduces the follow-
ing new calls: glXGetFBConfigs, glXGetFBConfigAttrib,
glXGetVisualFromFBConfig, glXCreateWindow, glXDestroyWindow,
connection. Thus if 1.3 is returned, both the client and server support
GLX 1.3. You can also check the GLX version at compile time: GLX_VER-
SION_1_1 will be defined in glx.h if GLX 1.1 calls are supported,
GLX_VERSION_1_2 will be defined if GLX 1.2 calls are supported, and
GLX_VERSION_1_3 will be defined if GLX 1.3 calls are supported.
SEE ALSO
glIntro, glFinish, glFlush, glXChooseVisual, glXCopyContext,
glXCreateContext, glXCreateGLXPixmap, glXDestroyContext,
glXGetClientString, glXGetConfig, glXIsDirect, glXMakeCurrent,
glXQueryExtension, glXQueryExtensionsString, glXQueryServerString,
glXQueryVersion, glXSwapBuffers, glXUseXFont, glXWaitGL, glXWaitX,
glXGetFBConfigs, glXGetFBConfigAttrib, glXGetVisualFromFBConfig,
glXCreateWindow, glXDestroyWindow, glXCreatePixmap, glXDestroyPixmap,
glXCreatePbuffer, glXDestroyPbuffer, glXQueryDrawable,
glXCreateNewContext, glXMakeContextCurrent, glXGetCurrentReadDrawable,
glXGetCurrentDisplay, glXQueryContext, glXSelectEvent,
glXGetSelectedEvent. XCreateColormap, XCreateWindow, XSync
GLXINTRO(3G)
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