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                          Mesa Cygwin/X11 Information


If you installed X11 (packages xorg-x11-devel and xorg-x11-bin-dlls ) with the 
latest setup.exe from Cygwin the GL (Mesa) libraries and include are already 
installed in /usr/X11R6. 

The following will explain how to "replace" them.


How to compile Mesa on Cygwin/X11 systems:

1. Shared libs:
    type 'make cygwin-sl'.

    When finished, the Mesa DLL will be in the Mesa-x.y/lib/ and 
    Mesa-x.y/bin directories.

2. Static libs:
    type 'make cygwin-static'.
    When finished, the Mesa libraries will be in the Mesa-x.y/lib/ directory.

Header and library files:
   After you've compiled Mesa and tried the demos I recommend the following
   procedure for "installing" Mesa.

   Copy the Mesa include/GL directory to /usr/X11R6/include:
	cp -a include/GL /usr/X11R6/include

   Copy the Mesa library files to /usr/X11R6/lib:
	cp -a lib/* /usr/X11R6ocal/lib

   Copy the Mesa bin files (used by the DLL stuff) to /usr/X11R6/bin:
	cp -a lib/cyg* /usr/X11R6/bin

Xt/Motif widgets:
   If you want to use Mesa or OpenGL in your Xt/Motif program you can build
   the widgets found in either the widgets-mesa or widgets-sgi directories.
   The former were written for Mesa and the later are the original SGI
   widgets.  Look in those directories for more information.
   For the Motif widgets you must have downloaded the lesstif package.

Using the library

Configuration options:
   The file src/mesa/main/config.h has many parameters which you can adjust
   such as maximum number of lights, clipping planes, maximum texture size,
   etc.  In particular, you may want to change DEPTH_BITS from 16 to 32
   if a 16-bit depth buffer isn't precise enough for your application.

Shared libraries:
   If you compile shared libraries (Win32 DLLS) you may have to set an 
   environment variable to specify where the Mesa libraries are located.  
   Set the PATH variable to include /your-dir/Mesa-2.6/bin.   
   Otherwise, when you try to run a demo it may fail with a message saying 
   that one or more DLL couldn't be found.

Xt/Motif Widgets:
   Two versions of the Xt/Motif OpenGL drawing area widgets are included:

      widgets-sgi/	SGI's stock widgets
      widgets-mesa/	Mesa-tuned widgets

   Look in those directories for details

   Togl is an OpenGL/Mesa widget for Tcl/Tk.
   See for more information.

X Display Modes:
   Mesa supports RGB(A) rendering into almost any X visual type and depth.

   The glXChooseVisual function tries its best to pick an appropriate visual
   for the given attribute list.  However, if this doesn't suit your needs
   you can force Mesa to use any X visual you want (any supported by your
   X server that is) by setting the MESA_RGB_VISUAL and MESA_CI_VISUAL
   environment variables.  When an RGB visual is requested, glXChooseVisual
   will first look if the MESA_RGB_VISUAL variable is defined.  If so, it
   will try to use the specified visual.  Similarly, when a color index
   visual is requested, glXChooseVisual will look for the MESA_CI_VISUAL

   The format of accepted values is:  <visual-class> <depth>
   Here are some examples:

   using the C-shell:
	% setenv MESA_RGB_VISUAL "TrueColor 8"		// 8-bit TrueColor
	% setenv MESA_CI_VISUAL "PseudoColor 12"	// 12-bit PseudoColor
	% setenv MESA_RGB_VISUAL "PseudoColor 8"	// 8-bit PseudoColor

   using the KornShell:
	$ export MESA_RGB_VISUAL="TrueColor 8"
	$ export MESA_CI_VISUAL="PseudoColor 12"
	$ export MESA_RGB_VISUAL="PseudoColor 8"

Double buffering:
   Mesa can use either an X Pixmap or XImage as the backbuffer when in
   double buffer mode.  Using GLX, the default is to use an XImage.  The
   MESA_BACK_BUFFER environment variable can override this.  The valid
   values for MESA_BACK_BUFFER are:  Pixmap and XImage (only the first
   letter is checked, case doesn't matter).

   A pixmap is faster when drawing simple lines and polygons while an
   XImage is faster when Mesa has to do pixel-by-pixel rendering.  If you
   need depth buffering the XImage will almost surely be faster.  Exper-
   iment with the MESA_BACK_BUFFER variable to see which is faster for
   your application.  

   When using Mesa directly or with GLX, it's up to the application writer
   to create a window with an appropriate colormap.  The aux, tk, and GLUT
   toolkits try to minimize colormap "flashing" by sharing colormaps when
   possible.  Specifically, if the visual and depth of the window matches
   that of the root window, the root window's colormap will be shared by
   the Mesa window.  Otherwise, a new, private colormap will be allocated.

   When sharing the root colormap, Mesa may be unable to allocate the colors
   it needs, resulting in poor color quality.  This can happen when a
   large number of colorcells in the root colormap are already allocated.
   To prevent colormap sharing in aux, tk and GLUT, define the environment
   variable MESA_PRIVATE_CMAP.  The value isn't significant.

Gamma correction:
   To compensate for the nonlinear relationship between pixel values
   and displayed intensities, there is a gamma correction feature in
   Mesa.  Some systems, such as Silicon Graphics, support gamma
   correction in hardware (man gamma) so you won't need to use Mesa's
   gamma facility.  Other systems, however, may need gamma adjustment
   to produce images which look correct.  If in the past you thought
   Mesa's images were too dim, read on.

   Gamma correction is controlled with the MESA_GAMMA environment
   variable.  Its value is of the form "Gr Gg Gb" or just "G" where
   Gr is the red gamma value, Gg is the green gamma value, Gb is the
   blue gamma value and G is one gamma value to use for all three
   channels.  Each value is a positive real number typically in the
   range 1.0 to 2.5.  The defaults are all 1.0, effectively disabling
   gamma correction.  Examples using csh:

	% setenv MESA_GAMMA "2.3 2.2 2.4"	// separate R,G,B values
	% setenv MESA_GAMMA "2.0"		// same gamma for R,G,B

   The demos/gamma.c program may help you to determine reasonable gamma
   value for your display.  With correct gamma values, the color intensities
   displayed in the top row (drawn by dithering) should nearly match those
   in the bottom row (drawn as grays).

   Alex De Bruyn reports that gamma values of 1.6, 1.6 and 1.9 work well
   on HP displays using the HP-ColorRecovery technology.

   Mesa implements gamma correction with a lookup table which translates
   a "linear" pixel value to a gamma-corrected pixel value.  There is a
   small performance penalty.  Gamma correction only works in RGB mode.
   Also be aware that pixel values read back from the frame buffer will
   not be "un-corrected" so glReadPixels may not return the same data
   drawn with glDrawPixels.

   For more information about gamma correction see:

Overlay Planes

   Overlay planes in the frame buffer are supported by Mesa but require
   hardware and X server support.  To determine if your X server has
   overlay support you can test for the SERVER_OVERLAY_VISUALS property:

	xprop -root | grep SERVER_OVERLAY_VISUALS

HPCR glClear(GL_COLOR_BUFFER_BIT) dithering

   If you set the MESA_HPCR_CLEAR environment variable then dithering
   will be used when clearing the color buffer.  This is only applicable
   to HP systems with the HPCR (Color Recovery) system.

   There are three Mesa-specific GLX extensions at this time.


      This extension adds the GLX function:

         GLXPixmap glXCreateGLXPixmapMESA( Display *dpy, XVisualInfo *visual,
                                           Pixmap pixmap, Colormap cmap )

      It is an alternative to the standard glXCreateGLXPixmap() function.
      Since Mesa supports RGB rendering into any X visual, not just True-
      Color or DirectColor, Mesa needs colormap information to convert RGB
      values into pixel values.  An X window carries this information but a
      pixmap does not.  This function associates a colormap to a GLX pixmap.
      See the xdemos/glxpixmap.c file for an example of how to use this


      Mesa associates a set of ancillary (depth, accumulation, stencil and
      alpha) buffers with each X window it draws into.  These ancillary
      buffers are allocated for each X window the first time the X window
      is passed to glXMakeCurrent().  Mesa, however, can't detect when an
      X window has been destroyed in order to free the ancillary buffers.

      The best it can do is to check for recently destroyed windows whenever
      the client calls the glXCreateContext() or glXDestroyContext()
      functions.  This may not be sufficient in all situations though.

      The GLX_MESA_release_buffers extension allows a client to explicitly
      deallocate the ancillary buffers by calling glxReleaseBuffersMESA()
      just before an X window is destroyed.  For example:

         #ifdef GLX_MESA_release_buffers
            glXReleaseBuffersMESA( dpy, window );
         XDestroyWindow( dpy, window );

      This extension is new in Mesa 2.0.


      This extension adds the glXCopySubBufferMESA() function.  It works
      like glXSwapBuffers() but only copies a sub-region of the window
      instead of the whole window.

      This extension is new in Mesa version 2.6

Summary of X-related environment variables:
   MESA_RGB_VISUAL - specifies the X visual and depth for RGB mode (X only)
   MESA_CI_VISUAL - specifies the X visual and depth for CI mode (X only)
   MESA_BACK_BUFFER - specifies how to implement the back color buffer (X only)
   MESA_PRIVATE_CMAP - force aux/tk libraries to use private colormaps (X only)
   MESA_GAMMA - gamma correction coefficients (X only)

README.CYGWIN - lassauge April 2004 - based on README.X11