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

    <para>
      Written by &name-lionel-ulmer; <email>&email-lionel-ulmer;</email>,
      last modification : 2000/06/13
    </para>
    <para>
      (Extracted from <filename>wine/documentation/opengl</filename>)
    </para>

    <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 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 thread-safety</title>

        <para>
          After that, the script checks if the OpenGL library relies
          or not on the pthread library to provide thread safety (most
          'modern' OpenGL libraries do).
        </para>
        <para>
          If the OpenGL library explicitely links in libpthread (you
          can check it with a <command>ldd libGL.so</command>), you
          need to force OpenGL support by starting
          <command>configure</command> with the
          <parameter>--enable-opengl</parameter> flag.
        </para>
        <para>
          The reason to this is that Wine contains some hacks done by
          Ove to cohabit with pthread that are known to work well in
          most of the cases (glibc 2.1.x). On the other hand, we never
          got Wine to work with glibc 2.0.6. Thus, I deemed preferable
          to play it safe : by default, I suppose that the hack won't
          work and that it's the user's responsability to enable it.
        </para>
        <para>
          Anyway, it should be pretty safe to build with
          <parameter>--enable-opengl</parameter>.
        </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. There should
          be no problem here.
        </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>
        <para>
          If your library does not provide it, you are out of luck.
        </para>
        <note>
          <para>
            this is not completely true as one could rewrite a
            <function>glXGetProcAddressARB</function> replacement
            using <function>dlopen</function> and friends, but well,
            telling people to upgrade is easier :-).
          </para>
        </note>
      </sect2>
    </sect1>

    <sect1 id="opengl-configure">
      <title>How to configure</title>

      <para>
        Configuration is quite easy : once OpenGL support has been
        built in Wine, this internal OpenGL driver will be used each
        time an application tries to load
        <filename>opengl32.dll</filename>.
      </para>
      <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>.winerc</filename> / <filename>wine.ini</filename>
        in the [x11drv] section :
      </para>
      <programlisting>
DesktopDoubleBuffered = Y
      </programlisting>
      <para>
        and to run Wine with the <parameter>--desktop</parameter>
        option.
      </para>
    </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 braindead 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>graphics/x11drv/opengl.c</filename> (all these
              functions are part of Wine's graphic driver function
              pointer table and thus could be reimplented 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 - shortcomings</title>

      <sect2>
        <title>Missing GLU32.DLL</title>

        <para>
          GLU is a library that is layered upon OpenGL. There is a
          100% correspondence between the
          <filename>libGLU.so</filename> that is used on Linux and
          <filename>GLU32.DLL</filename>.
        </para>
        <para>
          As for the moment, I did not create a set of thunks to support this
          library natively in Wine (it would easy to do, but I am waiting for
          a better solution than adding another autogenerated thunk file), you
          can always download anywhere on the net (it's free) a
          <filename>GLU32.DLL</filename> file (by browsing, for example,
          <ulink url="http://ftpsearch.lycos.com/">
            http://ftpsearch.lycos.com/</ulink>).
        </para>
      </sect2>

      <sect2>
        <title>OpenGL not detected at configure time</title>

        <para>
          See section (I) for a detailed explanation of the
          <filename>configure</filename> requirements.
        </para>
      </sect2>

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

        <para>
          See section (II) for how to create the context
          double-buffered and thus preventing this flicker effect.
        </para>
      </sect2>

      <sect2>
        <title>Wine gives me the following error message : </title>

        <screen>
Extension defined in the OpenGL library but NOT in opengl_ext.c...
Please report (&email-lionel-ulmer;) !
        </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 :
        </para>

        <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>
          If you have this, run with <parameter>--debugmsg
            +opengl</parameter> and send me
          <email>&email-lionel-ulmer;</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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