2 files changed, 65 insertions, 0 deletions

diff --git a/src/drivers/Cocoa/Fl_Cocoa_Gl_Window_Driver.cxx b/src/drivers/Cocoa/Fl_Cocoa_Gl_Window_Driver.cxx
index 4d47c3015..b14ac6a17 100644
--- a/src/drivers/Cocoa/Fl_Cocoa_Gl_Window_Driver.cxx
+++ b/src/drivers/Cocoa/Fl_Cocoa_Gl_Window_Driver.cxx
@@ -304,6 +304,47 @@ FL_EXPORT NSOpenGLContext *fl_mac_glcontext(GLContext rc) {
 }
 
 
+/* macOS offers only core contexts when using GL3. This forbids to add
+ FLTK widgets to a GL3-using Fl_Gl_Window because these widgets are drawn
+ with the GL1-based Fl_OpenGL_Graphics_Driver. The solution implemented here
+ is to create, with public function fl_mac_prepare_add_widgets_to_GL3_win(),
+ an additional Fl_Gl_Window placed above and sized as the GL3-based window,
+ to give it a non opaque, GL1-based context, and to put the FLTK widgets
+ in that additional window.
+ */
+
+class transparentGlWindow : public Fl_Gl_Window { // utility class
+  bool need_remove_opacity;
+public:
+  transparentGlWindow(int x, int y, int w, int h) : Fl_Gl_Window(x, y, w, h) {
+    mode(FL_RGB8 | FL_ALPHA | FL_SINGLE);
+    need_remove_opacity = true;
+  }
+  void show() {
+    Fl_Gl_Window::show();
+    if (need_remove_opacity) {
+      need_remove_opacity = false;
+      Fl_Cocoa_Window_Driver *d = Fl_Cocoa_Window_Driver::driver(this);
+      d->remove_gl_context_opacity((NSOpenGLContext*)context());
+    }
+  }
+};
+
+
+Fl_Gl_Window *fl_mac_prepare_add_widgets_to_GL3_win(Fl_Gl_Window *gl3win) {
+  gl3win->begin();
+  transparentGlWindow *transp = new transparentGlWindow(0, 0,
+                        gl3win->w(), gl3win->h());
+  gl3win->end();
+  if (!gl3win->resizable()) gl3win->resizable(gl3win);
+  if (gl3win->shown()) {
+    transp->show();
+    gl3win->make_current();
+  }
+  return transp;
+}
+
+
 class Fl_Gl_Cocoa_Plugin : public Fl_Cocoa_Plugin {
 public:
   Fl_Gl_Cocoa_Plugin() : Fl_Cocoa_Plugin(name()) { }
diff --git a/src/glut_compatibility.cxx b/src/glut_compatibility.cxx
index 0a5a6b30e..011f9290b 100644
--- a/src/glut_compatibility.cxx
+++ b/src/glut_compatibility.cxx
@@ -30,6 +30,9 @@
 #  include "Fl_Screen_Driver.H"
 #  include <FL/glut.H>
 #  define MAXWINDOWS 32
+#  ifndef GL_CURRENT_PROGRAM
+#    define GL_CURRENT_PROGRAM 0x8B8D  // from glew.h
+#  endif
 
 static Fl_Glut_Window *windows[MAXWINDOWS+1];
 
@@ -54,6 +57,27 @@ void Fl_Glut_Window::draw() {
   indraw = 1;
   if (!valid()) {reshape(pixel_w(),pixel_h()); valid(1);}
   display();
+  if (children()) {
+    if ((mode() & FL_OPENGL3)) {
+#ifndef __APPLE__
+      typedef void (*glUseProgram_type)(GLint);
+      static glUseProgram_type glUseProgram_f = NULL;
+      if (!glUseProgram_f) {
+        Fl_Gl_Window_Driver *dr = Fl_Gl_Window_Driver::driver(this);
+        glUseProgram_f = (glUseProgram_type)dr->GetProcAddress("glUseProgram");
+      }
+      GLint current_prog = 0;
+      glGetIntegerv(GL_CURRENT_PROGRAM, &current_prog);
+      // Switch from GL3-style to GL1-style drawing;
+      // good under Windows, X11 and Wayland; impossible under macOS.
+      glUseProgram_f(0);
+      // Draw FLTK child widgets
+      Fl_Gl_Window::draw();
+      // Switch back to GL3-style drawing
+      glUseProgram_f((GLuint)current_prog);
+#endif // ! __APPLE__
+    } else Fl_Gl_Window::draw(); // Draw FLTK child widgets
+  }
   indraw = 0;
 }