Re: Getting OpenGL 4.5 working with GTKMM

[JLM <jlyonm protonmail com>]

Just to close the loop in case anyone else runs into this, the main
problem was that I hadn't called gtkGlArea's make_current() function.
This is necessary to make the OpenGL rendering context available for
subsequent commands.

Once I did that, both the Epoxy version number and the original
glewInit() functions work correctly. I had incorrectly thought that
rendering context was automatically made current either after
instantiating the widget, or at least in it's on_realize() signal
handler.

On Sun, 2021-04-11 at 12:41 +0000, JLM via gtkmm-list wrote:
> So I found this example:
>
> https://github.com/GNOME/gtkmm/blob/master/demos/gtk-demo/example_glarea.cc
>
> And it has #include <epoxy/gl.h> , and I thought, "what is that?"
>
> So I found this:
>
> https://github.com/anholt/libepoxy
>
> And, gee, it just works!
>
> I'm not sure if this is enough, becase epoxy_gl_version() returns 0,
> but the glArea->get_required_version() returns 4.5. I'll pretend it
> doesn't matter for now and bug someone (else?) later if I'm again at
> my
> wit's end.
>
> On Sun, 2021-04-11 at 01:52 +0000, JLM via gtkmm-list wrote:
> > I am trying to make use of OpenGL 4.5 in a gtkGlArea. The code
> > below
> > works. However, I have the OpenGL Programming Guide Ninth Edition,
> > and
> > it uses this instead of glClearColor:
> >
> >     static const float black[] = { 0.0, 0.0, 0.0, 0.0 };
> >     glClearBufferfv(GL_COLOR, 0, black);
> >
> > When I try to use that, the compile doesn't find it:
> >
> > gtkgl.cpp:32:5: error: 'glClearBufferfv' was not declared in this
> > scope; did you mean 'glReadBuffer'?
> >    32 |     glClearBufferfv(GL_COLOR, 0, black);
> >
> > I also tried #include <GL/glext.h> but that didn't help.
> >
> > So then I thought maybe I need to make use of GLEW. When I #include
> > <GL/glew.h>, that compiles at least. But, then I can't run GLEW's
> > setup:
> >
> >     GLenum glewError = glewInit();
> >     if(glewError != GLEW_OK)
> >     {
> >         std::cerr << "Error: " << glewGetErrorString(glewError) <<
> > std::endl;
> >     }
> >
> > When I run, it always says:
> >
> > Error: Missing GL version
> >
> > So then I found the gtkGlArea method, set_required_version, and set
> > it:
> >
> > gl
> > Area->set_required_version(4, 5);
> >
> > But that still didn't help. So then I thought maybe the GLEW init
> > needs
> > to be in the on_realize() section, as I saw that this is where you
> > put
> > OpenGL init stuff, but that still didn't work.
> >
> > So, what do I need to #include? Should I make use of GLEW, or does
> > GTK(MM) do everything necessary to get OpenGL already? Are there
> > any
> > tutorials or examples? Most everything I find is for OpenGL 3.3,
> > but I
> > don't know how to align that with the book I've got.
> >
> > Thanks for any help you can provide.
> >
> >
> > #include <gtkmm.h>
> > #include <iostream>
> > #include <GL/gl.h>
> > #include <GL/glu.h>
> >
> > Gtk::Window* pDialog = nullptr;
> >
> > static
> > void on_button_clicked()
> > {
> >     if(pDialog)
> >         pDialog->hide(); //hide() will cause main::run() to end.
> > }
> >
> > bool glRender(const Glib::RefPtr<Gdk::GLContext>&)
> > {
> >     glClearColor(1.0f, 0.3f, 0.3f, 1.0f);
> >     glClear(GL_COLOR_BUFFER_BIT);
> >     return true;
> > }
> >
> > int main (int argc, char **argv)
> > {
> >     auto app = Gtk::App
> > lication::create(argc, argv, "org.test");
> >
> >     //Load the GtkBuilder file and instantiate its widgets:
> >     auto refBuilder = Gtk::Builder::create();
> >     try
> >     {
> >         refBuilder->add_from_file("glarea.glade");
> >     }
> >     catch(const Glib::FileError& ex)
> >     {
> >         std::cerr << "FileError: " << ex.what() << std::endl;
> >         return 1;
> >     }
> >     catch(const Glib::MarkupError& ex)
> >     {
> >         std::cerr << "MarkupError: " << ex.what() << std::endl;
> >         return 1;
> >     }
> >     catch(const Gtk::BuilderError& ex)
> >     {
> >         std::cerr << "BuilderError: " << ex.what() << std::endl;
> >         return 1;
> >     }
> >
> >     //Get the GtkBuilder-instantiated Dialog:
> >     refBuilder->get_widget("Window", pDialog);
> >     if(pDialog)
> >     {
> >         //Get the GtkBuilder-instantiated Button, and connect a
> > signal
> > handler:
> >         Gtk::MenuItem* pButton = nullptr;
> >         refBuilder->get_widget("quitMenuItem", pButton);
> >         if(pButton)
> >         {
> >             pButton->signa
> > l_activate().connect( sigc::ptr_fun(on_button_clicked) );
> >         }
> >
> >         Gtk::GLArea* glArea = nullptr;
> >         refBuilder->get_widget("glarea", glArea);
> >         if(glArea)
> >         {
> >             glArea->signal_render().connect(sigc::ptr_fun(glRender)
> > );
> >         }
> >         app->run(*pDialog);
> >     }
> >
> >     delete pDialog;
> >
> >     return 0;
> > }
> >
> > _______________________________________________
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>
>
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