  <chapter id="opengl">
    <title>Wine and OpenGL</title>

    <sect1 id="opengl-required">
      <title>What is needed to have OpenGL support in Wine</title>

      <para>
        Basically, if you have a Linux OpenGL ABI compliant libGL
        (<ulink url="http://oss.sgi.com/projects/ogl-sample/ABI/">
          http://oss.sgi.com/projects/ogl-sample/ABI/</ulink>)
        installed on your computer, you should have everything 
	that is needed.
      </para>
      <para>
        To be more clear, I will detail one step after another what
        the <command>configure</command> script checks.
      </para>
      <para>
        If, after Wine compiles, OpenGL support is not compiled in,
        you can always check <filename>config.log</filename> to see
        which of the following points failed.
      </para>

      <sect2>
        <title>Header files</title>

        <para>
          The needed header files to build OpenGL support in Wine are :
        </para>

        <variablelist>
          <varlistentry>
            <term><filename>gl.h:</filename></term>
            <listitem>
              <para>
                the definition of all OpenGL core functions, types and enumerants
              </para>
            </listitem>
          </varlistentry>
          <varlistentry>
            <term><filename>glx.h:</filename></term>
            <listitem>
              <para>
                how OpenGL integrates in the X Window environment
              </para>
            </listitem>
          </varlistentry>
          <varlistentry>
            <term><filename>glext.h:</filename></term>
            <listitem>
              <para>
                the list of all registered OpenGL extensions
              </para>
            </listitem>
          </varlistentry>
        </variablelist>

        <para>
          The latter file (<filename>glext.h</filename>) is, as of
          now, not necessary to build Wine. But as this file can be
          easily obtained from SGI 
          (<ulink url="http://oss.sgi.com/projects/ogl-sample/ABI/glext.h">
            http://oss.sgi.com/projects/ogl-sample/ABI/glext.h</ulink>),
          and that all OpenGL should provide one, I decided to keep it here.
        </para>
      </sect2>

      <sect2>
        <title>OpenGL library itself</title>

        <para>
          To check for the presence of 'libGL' on the system, the
          script checks if it defines the
          <function>glXCreateContext</function> function.
        </para>
      </sect2>

      <sect2>
        <title>glXGetProcAddressARB function</title>

        <para>
          The core of Wine's OpenGL implementation (at least for all
          extensions) is the <function>glXGetProcAddressARB</function>
          function. Your OpenGL library needs to have this function
          defined for Wine to be able to support OpenGL.
        </para>
      </sect2>
    </sect1>

    <sect1 id="opengl-works">
      <title>How it all works</title>

      <para>
        The core OpenGL function calls are the same between Windows
        and Linux. So what is the difficulty to support it in Wine ?
        Well, there are two different problems :
      </para>

      <orderedlist>
        <listitem>
          <para>
            the interface to the windowing system is different for
            each OS. It's called 'GLX' for Linux (well, for X Window)
            and 'wgl' for Windows. Thus, one need first to emulate one
            (wgl) with the other (GLX).
          </para>
        </listitem>
        <listitem>
          <para>
            the calling convention between Windows (the 'Pascal'
            convention or 'stdcall') is different from the one used on
            Linux (the 'C' convention or 'cdecl'). This means that
            each call to an OpenGL function must be 'translated' and
            cannot be used directly by the Windows program.
          </para>
        </listitem>
      </orderedlist>

      <para>
        Add to this some brain-dead programs (using GL calls without
        setting-up a context or deleting three time the same context)
        and you have still some work to do :-)
      </para>

      <sect2>
        <title>The Windowing system integration</title>

        <para>
          This integration is done at two levels : 
        </para>

        <orderedlist>
          <listitem>
            <para>
              At GDI level for all pixel format selection routines (ie
              choosing if one wants a depth / alpha buffer, the size
              of these buffers, ...) and to do the 'page flipping' in
              double buffer mode. This is implemented in
              <filename>dlls/x11drv/opengl.c</filename> (all these
              functions are part of Wine's graphic driver function
              pointer table and thus could be reimplemented if ever Wine
              works on another Windowing system than X).
            </para>
          </listitem>
          <listitem>
            <para>
              In the <filename>OpenGL32.DLL</filename> itself for all
              other functionalities (context creation / deletion,
              querying of extension functions, ...). This is done in
              <filename>dlls/opengl32/wgl.c</filename>.
            </para>
          </listitem>
        </orderedlist>
      </sect2>

      <sect2>
        <title>The thunks</title>

        <para>
          The thunks are the Wine code that does the calling
          convention translation and they are auto-generated by a Perl
          script. In Wine's CVS tree, these thunks are already
          generated for you. Now, if you want to do it yourself, there
          is how it all works....
        </para>
        <para>
          The script is located in <filename>dlls/opengl32</filename>
          and is called <command>make_opengl</command>. It requires
          Perl5 to work and takes two arguments :
        </para>

        <orderedlist>
          <listitem>
            <para>
              The first is the path to the OpenGL registry. Now, you
              will all ask 'but what is the OpenGL registry ?' :-)
              Well, it's part of the OpenGL sample implementation
              source tree from SGI (more informations at this URL :
              <ulink url="http://oss.sgi.com/projects/ogl-sample/">
                http://oss.sgi.com/projects/ogl-sample/</ulink>. 
            </para>
            <para>
              To summarize, these files contain human-readable but
              easily parsed information on ALL OpenGL core functions
              and ALL registered extensions (for example the
              prototype, the OpenGL version, ...).
            </para>
          </listitem>
          <listitem>
            <para>
              the second is the OpenGL version to 'simulate'. This
              fixes the list of functions that the Windows application
              can link directly to without having to query them from
              the OpenGL driver. Windows is based, for now, on OpenGL
              1.1, but the thunks that are in the CVS tree are
              generated for OpenGL 1.2.
            </para>
            <para>
              This option can have three values:
              <literal>1.0</literal>, <literal>1.1</literal> and
              <literal>1.2</literal>.
            </para>
          </listitem>
        </orderedlist>

        <para>
          This script generates three files :
        </para>

        <orderedlist>
          <listitem>
            <para>
              <filename>opengl32.spec</filename> gives Wine's linker
              the signature of all function in the
              <filename>OpenGL32.DLL</filename> library so that the
              application can link them. Only 'core' functions are
              listed here.
            </para>
          </listitem>
          <listitem>
            <para>
              <filename>opengl_norm.c</filename> contains all the
              thunks for the 'core' functions. Your OpenGL library
              must provide ALL the function used in this file as these
              are not queried at run time.
            </para>
          </listitem>
          <listitem>
            <para>
              <filename>opengl_ext.c</filename> contains all the
              functions that are not part of the 'core' functions.
              Contrary to the thunks in
              <filename>opengl_norm.c</filename>, these functions do
              not depend at all on what your libGL provides. 
            </para>
            <para>
              In fact, before using one of these thunks, the Windows
              program first needs to 'query' the function pointer. At
              this point, the corresponding thunk is useless. But as
              we first query the same function in libGL and store the
              returned function pointer in the thunk, the latter
              becomes functional.
            </para>
          </listitem>
        </orderedlist>
      </sect2>
    </sect1>

    <sect1 id="opengl-problems">
      <title>Known problems</title>

      <sect2>
        <title>When running an OpenGL application, the screen flickers</title>

        <para>
          Due to restrictions (that do not exist in Windows) on OpenGL
          contexts, if you want to prevent the screen to flicker when
          using OpenGL applications (all games are using double-buffered
          contexts), you need to set the following option in your
          <filename>~/.wine/config</filename> file
          in the <literal>[x11drv]</literal> section:
          <programlisting>
DesktopDoubleBuffered = Y
          </programlisting>
          and to run Wine in desktop mode.
        </para>
      </sect2>

      <sect2>
        <title>Unknown extension error message:</title>

        <screen>
Extension defined in the OpenGL library but NOT in opengl_ext.c...
Please report (lionel.ulmer@free.fr) !
        </screen>

        <para>
          This means that the extension requested by the application
          is found in the libGL used by Linux (ie the call to
          <function>glXGetProcAddressARB</function> returns a
          non-<constant>NULL</constant> pointer) but that this string
          was NOT found in Wine's extension registry.
        </para>
        <para>
          This can come from two causes:
        <orderedlist>
          <listitem>
            <para>
              The <filename>opengl_ext.c</filename> file is too old
              and needs to be generated again.
            </para>
          </listitem>
          <listitem>
            <para>
              Use of obsolete extensions that are not supported
              anymore by SGI or of 'private' extensions that are not
              registered. An example of the former are
              <function>glMTexCoord2fSGIS</function> and
              <function>glSelectTextureSGIS</function> as used by
              Quake 2 (and apparently also by old versions of Half
              Life). If documentation can be found on these functions,
              they can be added to Wine's extension set.
            </para>
          </listitem>
        </orderedlist>
        </para>

        <para>
          If you have this, run with <parameter>WINEDEBUG=+opengl</parameter>
          and send me <email>lionel.ulmer@free.fr</email> the TRACE.
        </para>
      </sect2>

      <sect2>
        <title><filename>libopengl32.so</filename> is built but it is still not working</title>

        <para>
          This may be caused by some missing functions required by
          <filename>opengl_norm.c</filename> but that your Linux
          OpenGL library does not provide.
        </para>
        <para>
          To check for this, do the following steps :
        </para>

        <orderedlist>
          <listitem>
            <para>
              create a dummy <filename>.c</filename> file :
            </para>
            <programlisting>
int main(void)
{
    return 0;
}
            </programlisting>
          </listitem>
          <listitem>
            <para>
              try to compile it by linking both libwine and
              libopengl32 (this command line supposes that you
              installed the Wine libraries in
              <filename>/usr/local/lib</filename>, YMMV) :
            </para>
            <programlisting>
gcc dummy.c -L/usr/local/lib -lwine -lopengl32
            </programlisting>
          </listitem>
          <listitem>
            <para>
              if it works, the problem is somewhere else (and you can
              send me an email). If not, you could re-generate the
              thunk files for OpenGL 1.1 for example (and send me your
              OpenGL version so that this problem can be detected at
              configure time).
            </para>
          </listitem>
        </orderedlist>
      </sect2>
    </sect1>
  </chapter>

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