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257 lines
9.9 KiB
Plaintext
257 lines
9.9 KiB
Plaintext
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Mesa Cygwin/X11 Information
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WARNING
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=======
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If you installed X11 (packages xorg-x11-devel and xorg-x11-bin-dlls ) with the
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latest setup.exe from Cygwin the GL (Mesa) libraries and include are already
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installed in /usr/X11R6.
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The following will explain how to "replace" them.
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Installation
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============
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How to compile Mesa on Cygwin/X11 systems:
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1. Shared libs:
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type 'make cygwin-sl'.
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When finished, the Mesa DLL will be in the Mesa-x.y/lib/ and
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Mesa-x.y/bin directories.
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2. Static libs:
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type 'make cygwin-static'.
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When finished, the Mesa libraries will be in the Mesa-x.y/lib/ directory.
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Header and library files:
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After you've compiled Mesa and tried the demos I recommend the following
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procedure for "installing" Mesa.
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Copy the Mesa include/GL directory to /usr/X11R6/include:
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cp -a include/GL /usr/X11R6/include
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Copy the Mesa library files to /usr/X11R6/lib:
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cp -a lib/* /usr/X11R6ocal/lib
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Copy the Mesa bin files (used by the DLL stuff) to /usr/X11R6/bin:
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cp -a lib/cyg* /usr/X11R6/bin
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Xt/Motif widgets:
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If you want to use Mesa or OpenGL in your Xt/Motif program you can build
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the widgets found in either the widgets-mesa or widgets-sgi directories.
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The former were written for Mesa and the later are the original SGI
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widgets. Look in those directories for more information.
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For the Motif widgets you must have downloaded the lesstif package.
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Using the library
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=================
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Configuration options:
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The file src/mesa/main/config.h has many parameters which you can adjust
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such as maximum number of lights, clipping planes, maximum texture size,
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etc. In particular, you may want to change DEPTH_BITS from 16 to 32
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if a 16-bit depth buffer isn't precise enough for your application.
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Shared libraries:
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If you compile shared libraries (Win32 DLLS) you may have to set an
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environment variable to specify where the Mesa libraries are located.
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Set the PATH variable to include /your-dir/Mesa-2.6/bin.
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Otherwise, when you try to run a demo it may fail with a message saying
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that one or more DLL couldn't be found.
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Xt/Motif Widgets:
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Two versions of the Xt/Motif OpenGL drawing area widgets are included:
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widgets-sgi/ SGI's stock widgets
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widgets-mesa/ Mesa-tuned widgets
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Look in those directories for details
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Togl:
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Togl is an OpenGL/Mesa widget for Tcl/Tk.
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See http://togl.sourceforge.net for more information.
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X Display Modes:
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Mesa supports RGB(A) rendering into almost any X visual type and depth.
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The glXChooseVisual function tries its best to pick an appropriate visual
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for the given attribute list. However, if this doesn't suit your needs
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you can force Mesa to use any X visual you want (any supported by your
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X server that is) by setting the MESA_RGB_VISUAL and MESA_CI_VISUAL
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environment variables. When an RGB visual is requested, glXChooseVisual
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will first look if the MESA_RGB_VISUAL variable is defined. If so, it
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will try to use the specified visual. Similarly, when a color index
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visual is requested, glXChooseVisual will look for the MESA_CI_VISUAL
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variable.
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The format of accepted values is: <visual-class> <depth>
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Here are some examples:
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using the C-shell:
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% setenv MESA_RGB_VISUAL "TrueColor 8" // 8-bit TrueColor
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% setenv MESA_CI_VISUAL "PseudoColor 12" // 12-bit PseudoColor
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% setenv MESA_RGB_VISUAL "PseudoColor 8" // 8-bit PseudoColor
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using the KornShell:
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$ export MESA_RGB_VISUAL="TrueColor 8"
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$ export MESA_CI_VISUAL="PseudoColor 12"
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$ export MESA_RGB_VISUAL="PseudoColor 8"
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Double buffering:
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Mesa can use either an X Pixmap or XImage as the backbuffer when in
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double buffer mode. Using GLX, the default is to use an XImage. The
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MESA_BACK_BUFFER environment variable can override this. The valid
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values for MESA_BACK_BUFFER are: Pixmap and XImage (only the first
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letter is checked, case doesn't matter).
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A pixmap is faster when drawing simple lines and polygons while an
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XImage is faster when Mesa has to do pixel-by-pixel rendering. If you
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need depth buffering the XImage will almost surely be faster. Exper-
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iment with the MESA_BACK_BUFFER variable to see which is faster for
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your application.
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Colormaps:
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When using Mesa directly or with GLX, it's up to the application writer
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to create a window with an appropriate colormap. The aux, tk, and GLUT
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toolkits try to minimize colormap "flashing" by sharing colormaps when
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possible. Specifically, if the visual and depth of the window matches
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that of the root window, the root window's colormap will be shared by
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the Mesa window. Otherwise, a new, private colormap will be allocated.
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When sharing the root colormap, Mesa may be unable to allocate the colors
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it needs, resulting in poor color quality. This can happen when a
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large number of colorcells in the root colormap are already allocated.
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To prevent colormap sharing in aux, tk and GLUT, define the environment
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variable MESA_PRIVATE_CMAP. The value isn't significant.
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Gamma correction:
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To compensate for the nonlinear relationship between pixel values
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and displayed intensities, there is a gamma correction feature in
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Mesa. Some systems, such as Silicon Graphics, support gamma
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correction in hardware (man gamma) so you won't need to use Mesa's
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gamma facility. Other systems, however, may need gamma adjustment
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to produce images which look correct. If in the past you thought
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Mesa's images were too dim, read on.
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Gamma correction is controlled with the MESA_GAMMA environment
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variable. Its value is of the form "Gr Gg Gb" or just "G" where
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Gr is the red gamma value, Gg is the green gamma value, Gb is the
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blue gamma value and G is one gamma value to use for all three
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channels. Each value is a positive real number typically in the
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range 1.0 to 2.5. The defaults are all 1.0, effectively disabling
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gamma correction. Examples using csh:
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% setenv MESA_GAMMA "2.3 2.2 2.4" // separate R,G,B values
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% setenv MESA_GAMMA "2.0" // same gamma for R,G,B
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The demos/gamma.c program may help you to determine reasonable gamma
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value for your display. With correct gamma values, the color intensities
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displayed in the top row (drawn by dithering) should nearly match those
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in the bottom row (drawn as grays).
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Alex De Bruyn reports that gamma values of 1.6, 1.6 and 1.9 work well
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on HP displays using the HP-ColorRecovery technology.
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Mesa implements gamma correction with a lookup table which translates
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a "linear" pixel value to a gamma-corrected pixel value. There is a
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small performance penalty. Gamma correction only works in RGB mode.
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Also be aware that pixel values read back from the frame buffer will
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not be "un-corrected" so glReadPixels may not return the same data
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drawn with glDrawPixels.
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For more information about gamma correction see:
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http://www.inforamp.net/~poynton/notes/colour_and_gamma/GammaFAQ.html
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Overlay Planes
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Overlay planes in the frame buffer are supported by Mesa but require
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hardware and X server support. To determine if your X server has
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overlay support you can test for the SERVER_OVERLAY_VISUALS property:
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xprop -root | grep SERVER_OVERLAY_VISUALS
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HPCR glClear(GL_COLOR_BUFFER_BIT) dithering
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If you set the MESA_HPCR_CLEAR environment variable then dithering
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will be used when clearing the color buffer. This is only applicable
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to HP systems with the HPCR (Color Recovery) system.
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Extensions
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==========
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There are three Mesa-specific GLX extensions at this time.
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GLX_MESA_pixmap_colormap
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This extension adds the GLX function:
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GLXPixmap glXCreateGLXPixmapMESA( Display *dpy, XVisualInfo *visual,
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Pixmap pixmap, Colormap cmap )
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It is an alternative to the standard glXCreateGLXPixmap() function.
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Since Mesa supports RGB rendering into any X visual, not just True-
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Color or DirectColor, Mesa needs colormap information to convert RGB
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values into pixel values. An X window carries this information but a
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pixmap does not. This function associates a colormap to a GLX pixmap.
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See the xdemos/glxpixmap.c file for an example of how to use this
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extension.
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GLX_MESA_release_buffers
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Mesa associates a set of ancillary (depth, accumulation, stencil and
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alpha) buffers with each X window it draws into. These ancillary
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buffers are allocated for each X window the first time the X window
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is passed to glXMakeCurrent(). Mesa, however, can't detect when an
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X window has been destroyed in order to free the ancillary buffers.
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The best it can do is to check for recently destroyed windows whenever
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the client calls the glXCreateContext() or glXDestroyContext()
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functions. This may not be sufficient in all situations though.
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The GLX_MESA_release_buffers extension allows a client to explicitly
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deallocate the ancillary buffers by calling glxReleaseBuffersMESA()
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just before an X window is destroyed. For example:
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#ifdef GLX_MESA_release_buffers
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glXReleaseBuffersMESA( dpy, window );
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#endif
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XDestroyWindow( dpy, window );
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This extension is new in Mesa 2.0.
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GLX_MESA_copy_sub_buffer
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This extension adds the glXCopySubBufferMESA() function. It works
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like glXSwapBuffers() but only copies a sub-region of the window
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instead of the whole window.
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This extension is new in Mesa version 2.6
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Summary of X-related environment variables:
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MESA_RGB_VISUAL - specifies the X visual and depth for RGB mode (X only)
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MESA_CI_VISUAL - specifies the X visual and depth for CI mode (X only)
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MESA_BACK_BUFFER - specifies how to implement the back color buffer (X only)
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MESA_PRIVATE_CMAP - force aux/tk libraries to use private colormaps (X only)
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MESA_GAMMA - gamma correction coefficients (X only)
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----------------------------------------------------------------------
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README.CYGWIN - lassauge April 2004 - based on README.X11
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