glXIntro(3G)
glXIntro - Introduction to OpenGL in the X window system
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NAME glXIntro - Introduction to OpenGL in the X window system 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 rendered 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 rendering. 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 XCreateWindow or XCreatePixmap, respectively) with a matching visual must be created first. Call glXGetVisualFromFBConfig to obtain the necessary 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. Likewise, to create a GLX pixmap, call glXCreatePixmap. Pbuffers are created 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 context/drawable pair becomes the current context and current drawable, and is used by all OpenGL rendering commands until glXMakeContextCurrent is called with different arguments. Both core X and OpenGL commands can be used to operate on drawables, however, the X and OpenGL command streams are not synchronized. Synchronization can be explicitly specified using by calling glXWaitGL, glXWaitX, XSync, and XFlush. EXAMPLES Below is a minimal example of creating an RGBA-format, X window that's compatible with OpenGL using GLX 1.3 commands. The window is cleared to yellow when the program runs. The program does minimal error checking; all return values should be checked. #include <stdio.h> #include <stdlib.h> #include <GL/gl.h> #include <GL/glx.h> 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 component */ 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 == (Window) arg); } int main( int argc, char *argv[] ) { Display *dpy; Window xWin; 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 server\n" ); 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, &numReturned ); 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 ); /* Create a GLX window to associate the frame buffer configuration ** with the created X window */ glxWin = glXCreateWindow( dpy, fbConfigs[0], xWin, NULL ); /* Map the window to the screen, and wait for it to appear */ XMapWindow( dpy, xWin ); XIfEvent( dpy, &event, WaitForNotify, (XPointer) xWin ); /* Bind the GLX context to the Window */ glXMakeContextCurrent( dpy, glxWin, glxWin, context ); /* OpenGL rendering ... */ glClearColor( 1.0, 1.0, 0.0, 1.0 ); glClear( GL_COLOR_BUFFER_BIT ); 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 context/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. GLX EXTENSIONS The SGI_video_sync extension provides a means for synchronization with the video frame rate of a monitor--or, in the case of an interlaced monitor, with the field rate of the monitor. For more information see: glXGetVideoSyncSGI, glXWaitVideoSyncSGI. The SGI_swap_control extension provides new parameters that modify the semantics of glXSwapBuffers. With this extension an application can specify a minimum periodicity for color buffer swaps, measured in display retrace periods. For more information see glXSwapIntervalSGI. The EXT_import_context allows multiple X clients to share an indirect rendering context. Also, two convenience routines are added: one to get the display for the current context and one to retrieve the attributes that a context was created with. For more information see glXGetCurrentDisplayEXT, glXQueryContextInfoEXT, glXGetContextIDEXT, glXImportContextEXT, and glXFreeContextEXT. The EXT_visual_rating extension allows servers to identify a particular GLX visual as undesirable. A new visual attribute is introduced, providing a way for servers to specify caveats (e.g., slow or non- conformant) for a visual. The attribute may be queried using glXGetConfig; it is also used by glXChooseVisual to discriminate against visuals with caveats. This extension allows servers to export visuals with improved features or image quality, but lower performance or greater system burden, without having to have these visuals selected preferentially. The EXT_visual_info extension allows the user to request a particular X visual type to be associated with a GLX visual, and allows the user to query the X visual type underlying a GLX visual. In addition, this extension provides a means to request a visual with a transparent pixel and to query whether a visual supports a transparent pixel value and the value of the transparent pixel. The SGIX_fbconfig extension introduces a new way to describe the capabilities of a GLX drawable (i.e., to describe the depth of color buffer components and the type and size of ancillary buffers), removes the "similarity" requirement when making a context current to a drawable, and supports RGBA rendering to one- and two-component Windows and GLX Pixmaps. For more information see glXGetFBConfigAttribSGIX, glXChooseFBConfigSGIX, glXCreateGLXPixmapWithConfigSGIX, glXCreateContextWithConfigSGIX, glXGetVisualFromFBConfigSGIX, glXGetFBConfigFromVisualSGIX. The SGIX_pbuffer extension defines GLX pixel buffers, which are additional non-visible rendering buffers for an OpenGL renderer. GLX pixel buffers are typically allocated in non-visible frame buffer memory. They are intended to be "static" resources, in that a program will typically allocate them only once, rather than as a part of its rendering loop. Also the frame buffer resources that are associated with a GLX pixel buffer are static, and are deallocated only when the GLXPbuffer is destroyed, or, in the case of a unpreserved GLX pixel buffer, as a result of X server activity that changes its frame buffer requirements. For more information see glXCreateGLXPbufferSGIX, glXDestroyGLXPbufferSGIX, glXQueryGLXPbufferSGIX, glXSelectEventSGIX, glXGetSelectedEventSGIX. SGIX_pbuffer is only supported on RealityEngine, RealityEngine2, and VTX systems, InfiniteReality systems, Solid Impact systems, High Impact and Maximum Impact systems, O2 systems, and Octane2 VPro systems. The SGIX_dm_pbuffer extension, with the addition of a DigitalMedia attribute, defines a type of GLX pixel buffer that can acquire one or more of its renderable buffers from a DMbuffer generated by video, compression, or other media library. A single DigitalMedia pixel buffer can be associated with a sequence of DMbuffers having the same configuration, making them directly OpenGL readable and renderable. Frame buffer resources that are not acquired from the DMbuffer are identical to those of a standard GLX pixel buffer. For more information see glXCreateGLXPbufferSGIX, glXAssociateDMPbufferSGIX, DMbuffer, dmBufferGetGLPoolParams. SGIX_dm_pbuffer is only supported on O2 systems. The SGIS_multisample extension provides a mechanism to antialias all primitives. (This extension is described in more detail in glIntro.) In order to support multisampling both GLX and OpenGL had to be extended. The GLX portion of the extension, designated as GLX_SGIS_multisample, includes new visual attributes which can be specified when calling glXChooseVisual and glXGetConfig. SGIS_multisample is only supported on RealityEngine, RealityEngine2, and VTX systems, and InfiniteReality systems. The SGI_make_current_read extension allows OpenGL pixel operations to read pixel data from the buffers of one drawable and draw into the buffers of another. For example, pixels can be copied from one window into another, or from a GLX pixel buffer into a window. For more information see glXMakeCurrentReadSGI and glXGetCurrentReadDrawableSGI. SGI_make_current_read is only supported on RealityEngine, RealityEngine2, and VTX systems, InfiniteReality systems, Solid Impact systems, High Impact and Maximum Impact systems, O2 systems, and Octane2 VPro systems. The SGIX_video_source extension allows pixel data to be sourced from a video input stream. It defines a new type of drawable, GLXVideoSourceSGIX, that represents the drain node of a Video Library (VL) path. A GLXVideoSourceSGIX may be passed as a parameter to glXMakeCurrentReadSGI to indicate that pixel data should be read from the specified video source instead of from the framebuffer. For more information, see glXCreateGLXVideoSourceSGIX and glXDestroyGLXVideoSourceSGIX. SGIX_video_source is only supported on RealityEngine, RealityEngine2, and VTX systems, and InfiniteReality systems. The SGIX_video_resize extension allows the frame buffer to be resized to the output resolution of the video channel when glXSwapBuffers is called for the window that is bound to the video channel. SGIX_video_resize is only supported on InfiniteReality systems. USING GLX EXTENSIONS Procedure names and tokens for GLX extensions are either suffixed with EXT, SGI, SGIS or SGIX. The meaning of these suffixes is described in glIntro. 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 extension 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 compile 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, 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 following new calls: glXGetFBConfigs, glXGetFBConfigAttrib, glXGetVisualFromFBConfig, glXCreateWindow, glXDestroyWindow, glXCreatePixmap, glXDestroyPixmap, glXCreatePbuffer, glXDestroyPbuffer, glXQueryDrawable, glXCreateNewContext, glXMakeContextCurrent, glXGetCurrentReadDrawable, glXGetCurrentDisplay, glXQueryContext, glXSelectEvent, glXGetSelectedEvent. GLX 1.2 corresponds to OpenGL version 1.1 and introduced the following new call: glXGetCurrentDisplay. GLX 1.1 corresponds to OpenGL version 1.0 and introduces the following new calls: glXQueryExtensionsString, glXQueryServerString, and glXGetClientString. Call glXQueryVersion to determine at runtime what version of GLX is available. glXQueryVersion returns the version that is supported on the 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_VERSION_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 glXIntro, glXFinish, glXFlush, 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