diff options
Diffstat (limited to 'docs/xlibdriver.rst')
| -rw-r--r-- | docs/xlibdriver.rst | 47 |
1 files changed, 4 insertions, 43 deletions
diff --git a/docs/xlibdriver.rst b/docs/xlibdriver.rst index 11e89ae6b0e..8a7a58bc5f5 100644 --- a/docs/xlibdriver.rst +++ b/docs/xlibdriver.rst @@ -18,7 +18,8 @@ The unique features of the Xlib driver follows. X Visual Selection ------------------ -Mesa supports RGB(A) rendering into almost any X visual type and depth. +Mesa supports RGB(A) rendering into TrueColor and DirectColor visuals, for +any depth with a corresponding renderable OpenGL texture format. The glXChooseVisual function tries to choose the best X visual for the given attribute list. However, if this doesn't suit your needs you can @@ -36,11 +37,11 @@ Here are some examples: using csh: % setenv MESA_RGB_VISUAL "TrueColor 8" // 8-bit TrueColor - % setenv MESA_RGB_VISUAL "PseudoColor 8" // 8-bit PseudoColor + % setenv MESA_RGB_VISUAL "DirectColor 30" // 30-bit DirectColor using bash: $ export MESA_RGB_VISUAL="TrueColor 8" - $ export MESA_RGB_VISUAL="PseudoColor 8" + $ export MESA_RGB_VISUAL="DirectColor 30" Double Buffering ---------------- @@ -77,46 +78,6 @@ 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. -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 you believe that Mesa's images are 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: - -.. code-block:: console - - % export MESA_GAMMA="2.3 2.2 2.4" # separate R,G,B values - % export MESA_GAMMA="2.0" # same gamma for R,G,B - -The ``demos/gamma.c`` program in mesa/demos repository 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 the `Wikipedia -article <https://en.wikipedia.org/wiki/Gamma_correction>`__ - Overlay Planes -------------- |