glXIntro(3gl)

1GLXINTRO()                                                          GLXINTRO()
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NAME

6       glXIntro - Introduction to OpenGL in the X window system
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8

OVERVIEW

10       OpenGL  (called  GL  in  other pages) is a high-performance 3D-oriented
11       renderer.  It is available in the  X  window  system  through  the  GLX
12       extension.  To determine whether the GLX extension is supported by an X
13       server, and if so, what version is  supported,  call  glXQueryExtension
14       and glXQueryVersion.
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16       GLX  extended  servers  make  a  subset  of their visuals available for
17       OpenGL rendering.  Drawables created with these  visuals  can  also  be
18       rendered using the core X renderer and with the renderer of any other X
19       extension that is compatible with all core X visuals.
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21       GLX extends drawables with several  buffers  other  than  the  standard
22       color  buffer.  These buffers include back and auxiliary color buffers,
23       a depth buffer, a stencil buffer,  and  a  color  accumulation  buffer.
24       Some or all are included in each X visual that supports OpenGL.
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26       To render using OpenGL into an X drawable, you must first choose a vis‐
27       ual that defines the required OpenGL buffers.  glXChooseVisual  can  be
28       used to simplify selecting a compatible visual.  If more control of the
29       selection process is required, use XGetVisualInfo and  glXGetConfig  to
30       select among all the available visuals.
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32       Use the selected visual to create both a GLX context and an X drawable.
33       GLX contexts are created with glXCreateContext, and drawables are  cre‐
34       ated  with  either  XCreateWindow or glXCreateGLXPixmap.  Finally, bind
35       the context and the drawable together using glXMakeCurrent.  This  con‐
36       text/drawable  pair  becomes  the current context and current drawable,
37       and it is used by all OpenGL commands until  glXMakeCurrent  is  called
38       with different arguments.
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40       Both  core  X and OpenGL commands can be used to operate on the current
41       drawable.  The X and OpenGL command streams are not synchronized,  how‐
42       ever,  except  at  explicitly  created  boundaries generated by calling
43       glXWaitGL, glXWaitX, XSync, and glFlush.
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EXAMPLES

46       Below is the minimum code required to create an RGBA-format,  X  window
47       that's  compatible  with OpenGL and to clear it to yellow.  The code is
48       correct, but it does not include any  error  checking.   Return  values
49       dpy, vi, cx, cmap, and win should all be tested.
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51       #include <GL/glx.h> #include <GL/gl.h> #include <unistd.h>
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53       static  int  attributeListSgl[]  =  {      GLX_RGBA,      GLX_RED_SIZE,
54       1, /*get the deepest buffer with 1 red  bit*/       GLX_GREEN_SIZE,  1,
55            GLX_BLUE_SIZE,  1,      None };
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57       static  int  attributeListDbl[] = {      GLX_RGBA,      GLX_DOUBLE_BUF‐
58       FER, /*In case single buffering is not  supported*/       GLX_RED_SIZE,
59       1,      GLX_GREEN_SIZE, 1,      GLX_BLUE_SIZE,  1,      None };
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62       static Bool WaitForNotify(Display *d, XEvent *e, char *arg) {
63           return (e->type == MapNotify) && (e->xmap.window == (Window)arg); }
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65       int main(int argc, char **argv) {
66           Display *dpy;
67           XVisualInfo *vi;
68           Colormap cmap;
69           XSetWindowAttributes swa;
70           Window win;
71           GLXContext cx;
72           XEvent event;
73           int swap_flag = FALSE;
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75
76           /* get a connection */
77           dpy = XOpenDisplay(0);
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79           /* get an appropriate visual */
80           vi = glXChooseVisual(dpy, DefaultScreen(dpy), attributeListSgl);
81           if (vi == NULL) {
82              vi = glXChooseVisual(dpy, DefaultScreen(dpy), attributeListDbl);
83              swap_flag = TRUE;
84           }
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86           /* create a GLX context */
87           cx = glXCreateContext(dpy, vi, 0, GL_TRUE);
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89           /* create a color map */
90           cmap    =    XCreateColormap(dpy,    RootWindow(dpy,   vi->screen),
91                         vi->visual, AllocNone);
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93           /* create a window */
94           swa.colormap = cmap;
95           swa.border_pixel = 0;
96           swa.event_mask = StructureNotifyMask;
97           win = XCreateWindow(dpy, RootWindow(dpy, vi->screen),  0,  0,  100,
98       100,
99                               0, vi->depth, InputOutput, vi->visual,
100                               CWBorderPixel|CWColormap|CWEventMask, &swa);
101           XMapWindow(dpy, win);
102           XIfEvent(dpy, &event, WaitForNotify, (char*)win);
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104           /* connect the context to the window */
105           glXMakeCurrent(dpy, win, cx);
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107           /* clear the buffer */
108           glClearColor(1,1,0,1);
109           glClear(GL_COLOR_BUFFER_BIT);
110           glFlush();
111           if (swap_flag) glXSwapBuffers(dpy,win);
112
113           /* wait a while */
114           sleep(10); }
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NOTES

117       A  color map must be created and passed to XCreateWindow.  See the pre‐
118       ceding example code.
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120       A GLX context must be created and attached  to  an  X  drawable  before
121       OpenGL  commands can be executed.  OpenGL commands issued while no con‐
122       text/drawable pair is current result in undefined behavior.
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124       Exposure events indicate that all buffers associated with the specified
125       window  may  be damaged and should be repainted.  Although certain buf‐
126       fers of some visuals on some systems may never require repainting  (the
127       depth buffer, for example), it is incorrect to write a program assuming
128       that these buffers will not be damaged.
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130       GLX commands manipulate XVisualInfo structures rather than pointers  to
131       visuals  or  visual  IDs.  XVisualInfo structures contain visual, visu‐
132       alID, screen, and depth elements, as well as other X-specific  informa‐
133       tion.
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USING GLX EXTENSIONS

136       All  supported  GLX  extensions will have a corresponding definition in
137       glx.h and a token in the extension string  returned  by  glXQueryExten‐
138       sionsString.   For  example,  if  the EXT_visual_info extension is sup‐
139       ported, then this token will be defined in  glx.h  and  EXT_visual_info
140       will  appear  in  the  extension  string returned by glXQueryExtension‐
141       sString. The definitions in glx.h can be used at compile time to deter‐
142       mine  if  procedure  calls  corresponding  to an extension exist in the
143       library.
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145       OpenGL itself has also been extended. Refer to glIntro for more  infor‐
146       mation.
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GLX 1.1 and GLX 1.2

149       GLX  1.2  is  now supported. It is backward compatible with GLX 1.1 and
150       GLX 1.0.
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152       GLX 1.2 corresponds to OpenGL version 1.1 and introduces the  following
153       new call: glGetCurrentDisplay.
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155       GLX  1.1 corresponds to OpenGL version 1.0 and introduces the following
156       new calls: glXQueryExtensionsString, glXQueryServerString, and  glXGet‐
157       ClientString.
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159       Call  glQueryVersion  to  determine  at  runtime what version of GLX is
160       available. glQueryVersion returns the version that is supported on  the
161       connection. Thus if 1.2 is returned, both the client and server support
162       GLX 1.2.  You can also check the GLX version at compile time:  GLX_VER‐
163       SION_1_1  will  be  defined in glx.h if GLX 1.1 calls are supported and
164       GLX_VERSION_1_2 will be defined if GLX 1.2 calls are supported.
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NAME

OVERVIEW

EXAMPLES

NOTES

USING GLX EXTENSIONS

GLX 1.1 and GLX 1.2

SEE ALSO