Fix creation of OpenGL3+ context under X11 platform

The procedure given in https://www.khronos.org/opengl/wiki/Tutorial:_OpenGL_3.0_Context_Creation_(GLX)
is now followed. This gives access to contexts for the highest OpenGL version supported by the hardware
when flag FL_OPENGL3 is used in the call to Fl_Gl_Window::mode(int).

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.4@13021 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

2 files changed, 107 insertions, 9 deletions

diff --git a/src/Fl_Gl_Choice.H b/src/Fl_Gl_Choice.H
index bdee1c6c8..5c5b339ef 100644
--- a/src/Fl_Gl_Choice.H
+++ b/src/Fl_Gl_Choice.H
@@ -3,7 +3,7 @@
 //
 // OpenGL definitions for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2016 by Bill Spitzak and others.
+// Copyright 1998-2018 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -50,9 +50,13 @@
 
 #ifdef FL_CFG_GFX_XLIB
 #  include <GL/glx.h>
+#  if ! defined(GLX_VERSION_1_3)
+#    typedef void *GLXFBConfig;
+#  endif
 #  define FL_GL_CHOICE_PLATFORM_SPECIFIC_MEMBERS  \
       XVisualInfo *vis; /* the visual to use */ \
-      Colormap colormap; // a colormap for that visual
+      Colormap colormap; /* a colormap for that visual */ \
+      GLXFBConfig best_fb;
 #endif // FL_CFG_GFX_XLIB*/
 
 
diff --git a/src/Fl_Gl_Choice.cxx b/src/Fl_Gl_Choice.cxx
index 014635e14..3fbce41f7 100644
--- a/src/Fl_Gl_Choice.cxx
+++ b/src/Fl_Gl_Choice.cxx
@@ -231,6 +231,53 @@ void Fl_WinAPI_Gl_Window_Driver::delete_gl_context(GLContext context) {
 #ifdef FL_CFG_GFX_XLIB
 #  include <FL/platform.H>
 
+static XVisualInfo *gl3_getvisual(const int *blist, GLXFBConfig *pbestFB)
+{
+  int glx_major, glx_minor;
+  
+  // FBConfigs were added in GLX version 1.3.
+  if ( !glXQueryVersion(fl_display, &glx_major, &glx_minor) ||
+      ( ( glx_major == 1 ) && ( glx_minor < 3 ) ) || ( glx_major < 1 ) ) {
+    return NULL;
+  }
+  
+  //printf( "Getting matching framebuffer configs\n" );
+  int fbcount;
+  GLXFBConfig* fbc = glXChooseFBConfig(fl_display, DefaultScreen(fl_display), blist, &fbcount);
+  if (!fbc) {
+    //printf( "Failed to retrieve a framebuffer config\n" );
+    return NULL;
+  }
+  //printf( "Found %d matching FB configs.\n", fbcount );
+  
+  // Pick the FB config/visual with the most samples per pixel
+  int best_fbc = -1, worst_fbc = -1, best_num_samp = -1, worst_num_samp = 999;
+  for (int i = 0; i < fbcount; ++i)
+  {
+    XVisualInfo *vi = glXGetVisualFromFBConfig( fl_display, fbc[i] );
+    if (vi) {
+      int samp_buf, samples;
+      glXGetFBConfigAttrib(fl_display, fbc[i], GLX_SAMPLE_BUFFERS, &samp_buf);
+      glXGetFBConfigAttrib(fl_display, fbc[i], GLX_SAMPLES       , &samples );
+      /*printf( "  Matching fbconfig %d, visual ID 0x%2lx: SAMPLE_BUFFERS = %d, SAMPLES = %d\n",
+             i, vi -> visualid, samp_buf, samples );*/
+      if ( best_fbc < 0 || (samp_buf && samples > best_num_samp) )
+        best_fbc = i, best_num_samp = samples;
+      if ( worst_fbc < 0 || !samp_buf || samples < worst_num_samp )
+        worst_fbc = i, worst_num_samp = samples;
+    }
+    XFree(vi);
+  }
+  
+  GLXFBConfig bestFbc = fbc[ best_fbc ];
+  // Be sure to free the FBConfig list allocated by glXChooseFBConfig()
+  XFree(fbc);
+  // Get a visual
+  XVisualInfo *vi = glXGetVisualFromFBConfig(fl_display, bestFbc);
+  *pbestFB = bestFbc;
+  return vi;
+}
+
 Fl_Gl_Choice *Fl_X11_Gl_Window_Driver::find(int m, const int *alistp)
 {
   Fl_Gl_Choice *g = Fl_Gl_Window_Driver::find_begin(m, alistp);
@@ -286,18 +333,26 @@ Fl_Gl_Choice *Fl_X11_Gl_Window_Driver::find(int m, const int *alistp)
   }
   
   fl_open_display();
-  XVisualInfo *visp = glXChooseVisual(fl_display, fl_screen, (int *)blist);
+  XVisualInfo *visp = NULL;
+  GLXFBConfig best_fb = NULL;
+  if (m & FL_OPENGL3) {
+    visp = gl3_getvisual((const int *)blist, &best_fb);
+  }
   if (!visp) {
-#    if defined(GLX_VERSION_1_1) && defined(GLX_SGIS_multisample)
-    if (m&FL_MULTISAMPLE) return find(m&~FL_MULTISAMPLE,0);
-#    endif
-    return 0;
+    visp = glXChooseVisual(fl_display, fl_screen, (int *)blist);
+    if (!visp) {
+#     if defined(GLX_VERSION_1_1) && defined(GLX_SGIS_multisample)
+        if (m&FL_MULTISAMPLE) return find(m&~FL_MULTISAMPLE, 0);
+#     endif
+      return 0;
+    }
   }
   
   g = new Fl_Gl_Choice(m, alistp, first);
   first = g;
   
   g->vis = visp;
+  g->best_fb = best_fb;
   
   if (/*MaxCmapsOfScreen(ScreenOfDisplay(fl_display,fl_screen))==1 && */
       visp->visualid == fl_visual->visualid &&
@@ -306,13 +361,52 @@ Fl_Gl_Choice *Fl_X11_Gl_Window_Driver::find(int m, const int *alistp)
   else
     g->colormap = XCreateColormap(fl_display, RootWindow(fl_display,fl_screen),
                                   visp->visual, AllocNone);
-  
   return g;
 }
 
+static bool ctxErrorOccurred = false;
+static int ctxErrorHandler( Display *dpy, XErrorEvent *ev )
+{
+  ctxErrorOccurred = true;
+  return 0;
+}
 
 GLContext Fl_X11_Gl_Window_Driver::create_gl_context(Fl_Window* window, const Fl_Gl_Choice* g, int layer) {
-  return create_gl_context(g->vis);
+  GLContext shared_ctx = 0;
+  if (context_list && nContext) shared_ctx = context_list[0];
+  
+  typedef GLContext (*glXCreateContextAttribsARBProc)(Display*, GLXFBConfig, GLContext, Bool, const int*);
+  // It is not necessary to create or make current to a context before calling glXGetProcAddressARB
+  static glXCreateContextAttribsARBProc glXCreateContextAttribsARB =
+    (glXCreateContextAttribsARBProc)glXGetProcAddressARB((const GLubyte *)"glXCreateContextAttribsARB");
+  
+  GLContext ctx = 0;
+  // Check for the GLX_ARB_create_context extension string and the function.
+  // If either is not present, use GLX 1.3 context creation method.
+  const char *glxExts = glXQueryExtensionsString(fl_display, fl_screen);
+  if (g->best_fb && strstr(glxExts, "GLX_ARB_create_context") && glXCreateContextAttribsARB ) {
+    int context_attribs[] =
+    {
+      GLX_CONTEXT_MAJOR_VERSION_ARB, 3,
+      GLX_CONTEXT_MINOR_VERSION_ARB, 2,
+      //GLX_CONTEXT_FLAGS_ARB        , GLX_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB,
+      //GLX_CONTEXT_PROFILE_MASK_ARB , GLX_CONTEXT_CORE_PROFILE_BIT_ARB,
+      None
+    };
+    ctxErrorOccurred = false;
+    XErrorHandler oldHandler = XSetErrorHandler(&ctxErrorHandler);
+    ctx = glXCreateContextAttribsARB(fl_display, g->best_fb, shared_ctx, true, context_attribs);
+    XSync(fl_display, false); // Sync to ensure any errors generated are processed.
+    if (ctxErrorOccurred) ctx = 0;
+    XSetErrorHandler(oldHandler);
+  }
+  if (!ctx) { // use OpenGL 1-style context creation
+    ctx = glXCreateContext(fl_display, g->vis, shared_ctx, true);
+  }
+  if (ctx)
+    add_context(ctx);
+//glXMakeCurrent(fl_display, fl_xid(window), ctx);printf("%s\n", glGetString(GL_VERSION));
+  return ctx;
 }
 
 GLContext Fl_X11_Gl_Window_Driver::create_gl_context(XVisualInfo *vis) {