Editing OSMesa

OSMesa is used since Octave 4.0 for offscreen rendering from OpenGL toolkits FLTK and Qt.

This enables printing without a X display, for example when ssh'ing to a remote machine, or if the figure is invisible ({{bug|33180}}). 


= libOSMesa =

The minimum required version of OSMesa for Octave is 9.0.0. Versions < 9.0 show a strange bug where the return values of

  glGetIntegerv (GL_DEPTH_BITS, &z);
  glGetIntegerv (GL_STENCIL_BITS, &s);
  glGetIntegerv (GL_ACCUM_RED_BITS, &a);

contain arbitrary values and the rendered buffer is garbage. This only happens if OSMesa is linked together with Octave, standalone OSMesa examples works fine.

On Debian GNU/Linux 8.0 (jessie), Ubuntu 14.04 (trusty) and Fedora 21 there is no need to build OSMesa from source, just use your package manager which installs libosmesa > 10.0.

== Build libOSMesa from source ==

Needed for example for Debian wheezy or Ubuntu 12.04.5 which ships OSMesa 8.0.5.

  wget -nc ftp://ftp.freedesktop.org/pub/mesa/current/MesaLib-10.2.2.tar.bz2
  tar xjf MesaLib-10.2.2.tar.bz2
  cd Mesa-10.2.2/
  
  autoreconf -fi
  
  ./configure \
    CXXFLAGS="-O2 -g -DDEFAULT_SOFTWARE_DEPTH_BITS=31" \
    CFLAGS="-O2 -g -DDEFAULT_SOFTWARE_DEPTH_BITS=31" \
    --disable-xvmc \
    --disable-glx \
    --disable-dri \
    --with-dri-drivers="" \
    --with-gallium-drivers="" \
    --disable-shared-glapi \
    --disable-egl \
    --with-egl-platforms="" \
    --enable-osmesa \
    --enable-gallium-llvm=no \
    --prefix=/usr/local/mesa/10.2.2/classic
  make -j4
  # optional
  make check
  sudo make install

=== Floating point textures ===

Floating point textures are disabled by default due to patent restrictions. We should check if we can enable it with "--enable-texture-float"

== known problems ==

Unfortunately, there are several known problems with using on-screen Mesa and OSMesa at the same time.
The --without-OSMesa configure can be used to disable OSMesa if a problem is encountered.

* {{bug|44478}} segmentation fault when using proprietary Nvidia drivers
* {{bug|44979}} clumsy/missing configure check, relies on runtime failure
* {{bug|44338}} doesn't work at all on Windows
* [https://bugs.launchpad.net/bugs/1424059 LP #1424059] libosmesa6 is not installable on Ubuntu 14.04 with HWE updates
* {{bug|50479}} doesn't work at all with libglvnd, now standard in most distributions

=== workarounds ===

* Preload the Mesa libGL.so, for example
  export LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libGL.so

== Reporting Bugs ==

* Please include the output of
  glxinfo | grep "^OpenGL \(renderer\|core profile version\|vendor\)"