Improved documentation related to access to OpenGL 3 under X11 platform.

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.4@13022 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

FL/Fl_Gl_Window.H

@@ -151,7 +151,7 @@ public:
    - \c FL_DEPTH - depth buffer
    - \c FL_STENCIL - stencil buffer
    - \c FL_MULTISAMPLE - multisample antialiasing
-   - \c FL_OPENGL3 - use OpenGL version 3.0 or more when running Mac OS.
+   - \c FL_OPENGL3 - use OpenGL version 3.0 or more.
    
    FL_RGB and FL_SINGLE have a value of zero, so they
    are "on" unless you give FL_INDEX or FL_DOUBLE.
@@ -171,6 +171,9 @@ public:
    mode() must not be called within draw() since it
    changes the current context.
    
+   The FL_OPENGL3 flag is required to access OpenGL version 3 or more
+   under the X11 and MacOS platforms; it's optional under Windows.
+   
    \note On the <b>Windows and Unix/Linux platforms</b>, FLTK produces
    contexts for the highest OpenGL version supported by the hardware. Such contexts
    are also compatible with lower OpenGL versions. On the <b>Apple OS X
@@ -179,8 +182,7 @@ public:
    creates contexts adequate for OpenGL versions 1 and 2. To get contexts
    for OpenGL 3.0 or higher, the <tt>FL_OPENGL3</tt> flag and Mac OS
    version 10.7 or higher are required (in that case the context is NOT 
-   compatible with OpenGL versions 1 or 2). The <tt>FL_OPENGL3</tt> flag has no
+   compatible with OpenGL versions 1 or 2).
-   effect on non-Apple platforms.
    
    \version the <tt>FL_OPENGL3</tt> flag appeared in version 1.3.4
    */

documentation/src/opengl.dox

@@ -456,6 +456,9 @@ showing how to use OpenGL 3.0 (or higher versions) with FLTK in a cross-platform
 It contains also OpenGL3-glut-test.cxx which shows how to use FLTK's GLUT compatibility
 and OpenGL 3.
 
+To access OpenGL 3.0 (or higher versions), use the <tt>FL_OPENGL3</tt> flag
+when calling Fl_Gl_Window::mode(int a) or glutInitDisplayMode().
+
 <b>On the Windows and Unix/Linux platforms</b>, FLTK creates contexts
 implementing the highest OpenGL version supported by the hardware,
 which are also compatible with lower OpenGL versions. Thus, FLTK allows
@@ -463,9 +466,7 @@ source code targeting any version of OpenGL. Access to functions from OpenGL
 versions above 1.1 requires to load function pointers at runtime on these platforms.
 FLTK recommends to use the GLEW library to perform this. It is therefore
 necessary to install the GLEW library (see below).  <b>On the macOS platform</b>,
-FLTK creates by default contexts implementing OpenGL versions 1 or 2.
+MacOS 10.7 or above is required; GLEW is possible but not necessary.
-To access OpenGL 3.0 (or higher versions), use the <tt>FL_OPENGL3</tt> flag (see below).
-Mac OS 10.7 or above is required; GLEW is possible but not necessary.
 
 \par GLEW installation (Unix/Linux and Windows platforms)
 GLEW is available as a package for most Linux distributions and in source