240 lines
7.1 KiB
Plaintext
240 lines
7.1 KiB
Plaintext
.\" $XFree86$
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'\"! eqn | mmdoc
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'\"macro stdmacro
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.ds Vn Version 1.2
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.ds Dt 6 March 1997
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.ds Re Release 1.2.0
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.ds Dp Feb 16 02:56
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.ds Dm Feb 10 17:2
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.ds Xs 32008 15 xintro.gl
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.TH GLXINTRO
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.SH NAME
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glXIntro
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\- Introduction to OpenGL in the X window system
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.SH OVERVIEW
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OpenGL (called GL in other pages) is a high-performance 3D-oriented renderer.
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It is available in the X window system through the GLX extension.
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To determine whether the GLX extension is supported by an X server,
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and if so, what version is supported, call \f3glXQueryExtension\fP
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and \f3glXQueryVersion\fP.
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.P
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GLX extended servers make a subset of their visuals available
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for OpenGL rendering.
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Drawables created with these visuals can also be rendered using
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the core X renderer
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and with the renderer of any other X extension that is compatible
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with all core X visuals.
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.P
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GLX extends drawables with several buffers other than
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the standard color buffer.
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These buffers include back and auxiliary color buffers,
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a depth buffer,
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a stencil buffer,
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and a color accumulation buffer.
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Some or all are included in each X visual that supports OpenGL.
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.P
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To render using OpenGL into an X drawable,
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you must first choose a visual that defines the required OpenGL buffers.
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\f3glXChooseVisual\fP can be used to simplify selecting a compatible visual.
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If more control of the selection process is required,
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use \f3XGetVisualInfo\fP and \f3glXGetConfig\fP to select among
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all the available visuals.
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.P
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Use the selected visual to create both a GLX context and an X
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drawable.
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GLX contexts are created with \f3glXCreateContext\fP,
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and drawables are created with either \f3XCreateWindow\fP or
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\f3glXCreateGLXPixmap\fP.
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Finally,
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bind the context and the drawable together using \f3glXMakeCurrent\fP.
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This context/drawable pair becomes the current context and current
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drawable,
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and it is used by all OpenGL commands until \f3glXMakeCurrent\fP is
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called with different arguments.
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.P
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Both core X and OpenGL commands can be used to operate on the
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current drawable.
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The X and OpenGL command streams are not synchronized,
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however,
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except at explicitly created boundaries generated by calling
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\f3glXWaitGL\fP, \f3glXWaitX\fP, \f3XSync\fP, and \f3glFlush\fP.
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.SH EXAMPLES
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Below is the minimum code required to create an RGBA-format,
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X window that's compatible with OpenGL and to clear it to yellow.
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The code is correct,
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but it does not include any error checking.
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Return values \f2dpy\fP,
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\f2vi\fP,
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\f2cx\fP,
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\f2cmap\fP, and
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\f2win\fP should all be tested.
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.P
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.Ex
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\&#include <GL/glx.h>
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\&#include <GL/gl.h>
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\&#include <unistd.h>
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static int attributeListSgl[] = {
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GLX_RGBA,
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GLX_RED_SIZE, 1, /*get the deepest buffer with 1 red bit*/
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GLX_GREEN_SIZE, 1,
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GLX_BLUE_SIZE, 1,
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None };
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static int attributeListDbl[] = {
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GLX_RGBA,
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GLX_DOUBLE_BUFFER, /*In case single buffering is not supported*/
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GLX_RED_SIZE, 1,
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GLX_GREEN_SIZE, 1,
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GLX_BLUE_SIZE, 1,
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None };
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static Bool WaitForNotify(Display *d, XEvent *e, char *arg) {
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return (e->type == MapNotify) && (e->xmap.window == (Window)arg);
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}
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int main(int argc, char **argv) {
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Display *dpy;
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XVisualInfo *vi;
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Colormap cmap;
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XSetWindowAttributes swa;
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Window win;
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GLXContext cx;
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XEvent event;
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int swap_flag = FALSE;
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/* get a connection */
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dpy = XOpenDisplay(0);
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/* get an appropriate visual */
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vi = glXChooseVisual(dpy, DefaultScreen(dpy), attributeListSgl);
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if (vi == NULL) {
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vi = glXChooseVisual(dpy, DefaultScreen(dpy), attributeListDbl);
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swap_flag = TRUE;
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}
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/* create a GLX context */
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cx = glXCreateContext(dpy, vi, 0, GL_TRUE);
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/* create a color map */
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cmap = XCreateColormap(dpy, RootWindow(dpy, vi->screen),
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vi->visual, AllocNone);
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/* create a window */
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swa.colormap = cmap;
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swa.border_pixel = 0;
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swa.event_mask = StructureNotifyMask;
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win = XCreateWindow(dpy, RootWindow(dpy, vi->screen), 0, 0, 100, 100,
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0, vi->depth, InputOutput, vi->visual,
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CWBorderPixel|CWColormap|CWEventMask, &swa);
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XMapWindow(dpy, win);
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XIfEvent(dpy, &event, WaitForNotify, (char*)win);
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/* connect the context to the window */
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glXMakeCurrent(dpy, win, cx);
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/* clear the buffer */
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glClearColor(1,1,0,1);
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glClear(GL_COLOR_BUFFER_BIT);
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glFlush();
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if (swap_flag) glXSwapBuffers(dpy,win);
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/* wait a while */
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sleep(10);
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}
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.Ee
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.SH NOTES
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A color map must be created and passed to \f3XCreateWindow\fP.
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See the preceding example code.
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.P
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A GLX context must be created and attached to an X drawable before
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OpenGL commands can be executed.
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OpenGL commands issued while no context/drawable pair is current
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result in undefined behavior.
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.P
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Exposure events indicate that \f2all\fP buffers associated with the
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specified window may be damaged and should be repainted.
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Although certain buffers of some visuals on some systems
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may never require repainting
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(the depth buffer, for example),
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it is incorrect to write a program assuming that these buffers will
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not be damaged.
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.P
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GLX commands manipulate XVisualInfo structures rather than pointers to
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visuals or visual IDs.
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XVisualInfo structures contain \f2visual\fP,
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\f2visualID\fP,
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\f2screen\fP, and
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\f2depth\fP elements,
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as well as other X-specific information.
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.SH USING GLX EXTENSIONS
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All supported GLX extensions will have a corresponding definition in glx.h
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and a token in the extension string returned by \f3glXQueryExtensionsString\fP.
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For example, if the \f3EXT_visual_info\fP extension is supported,
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then this token will be defined in glx.h and \f3EXT_visual_info\fP
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will appear in the extension
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string returned by \f3glXQueryExtensionsString\fP. The definitions in glx.h
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can be used at compile time to determine if procedure calls corresponding
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to an extension exist in the library.
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.P
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OpenGL itself has also been extended. Refer to \f3glIntro\fP for more
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information.
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.P
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.SH GLX 1.1 and GLX 1.2
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GLX 1.2 is now supported. It is backward compatible with GLX 1.1 and
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GLX 1.0.
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.P
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GLX 1.2 corresponds to OpenGL version 1.1 and introduces the following
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new call: \f3glGetCurrentDisplay\fP.
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.P
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GLX 1.1 corresponds to OpenGL version 1.0 and introduces the
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following new calls:
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\f3glXQueryExtensionsString\fP, \f3glXQueryServerString\fP, and
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\f3glXGetClientString\fP.
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.P
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Call \f3glQueryVersion\fP
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to determine at runtime what version of GLX is available. \f3glQueryVersion\fP
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returns the version that is supported on the connection. Thus
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if 1.2 is returned, both the client and server support GLX 1.2.
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You can also check the GLX version at compile time: GLX_VERSION_1_1
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will be defined in glx.h if GLX 1.1 calls are supported and
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GLX_VERSION_1_2 will be defined if GLX 1.2 calls are supported.
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.SH SEE ALSO
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\f3glIntro\fP,
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\f3glFinish\fP,
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\f3glFlush\fP,
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\f3glXChooseVisual\fP,
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\f3glXCopyContext\fP,
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.br
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\f3glXCreateContext\fP,
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\f3glXCreateGLXPixmap\fP,
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\f3glXDestroyContext\fP,
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.br
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\f3glXGetClientString\fP,
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\f3glXGetConfig\fP,
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\f3glXIsDirect\fP,
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\f3glXMakeCurrent\fP,
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.br
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\f3glXQueryExtension\fP,
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\f3glXQueryExtensionsString\fP,
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\f3glXQueryServerString\fP,
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\f3glXQueryVersion\fP,
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\f3glXSwapBuffers\fP,
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\f3glXUseXFont\fP,
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\f3glXWaitGL\fP,
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\f3glXWaitX\fP,
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\f3XCreateColormap\fP,
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\f3XCreateWindow\fP,
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\f3XSync\fP
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