gtk.glarea

[gtk.glarea.GLArea] is a widget that allows drawing with OpenGL.

!An example GtkGLArea

[gtk.glarea.GLArea] sets up its own [gdk.glcontext.GLContext], and creates a custom GL framebuffer that the widget will do GL rendering onto. It also ensures that this framebuffer is the default GL rendering target when rendering. The completed rendering is integrated into the larger GTK scene graph as a texture.

In order to draw, you have to connect to the [gtk.glarea.GLArea.render] signal, or subclass [gtk.glarea.GLArea] and override the GtkGLAreaClass.render virtual function.

The [gtk.glarea.GLArea] widget ensures that the [gdk.glcontext.GLContext] is associated with the widget's drawing area, and it is kept updated when the size and position of the drawing area changes.

Drawing with GtkGLArea

The simplest way to draw using OpenGL commands in a [gtk.glarea.GLArea] is to create a widget instance and connect to the [gtk.glarea.GLArea.render] signal:

The render() function will be called when the [gtk.glarea.GLArea] is ready for you to draw its content:

The initial contents of the framebuffer are transparent.

static gboolean
render (GtkGLArea *area, GdkGLContext *context)
{
 // inside this function it's safe to use GL; the given
 // GdkGLContext has been made current to the drawable
 // surface used by the `GtkGLArea` and the viewport has
 // already been set to be the size of the allocation

 // we can start by clearing the buffer
 glClearColor (0, 0, 0, 0);
 glClear (GL_COLOR_BUFFER_BIT);

 // draw your object
 // draw_an_object ();

 // we completed our drawing; the draw commands will be
 // flushed at the end of the signal emission chain, and
 // the buffers will be drawn on the window
 return TRUE;
}

void setup_glarea (void)
{
 // create a GtkGLArea instance
 GtkWidget *gl_area = gtk_gl_area_new ();

 // connect to the "render" signal
 g_signal_connect (gl_area, "render", G_CALLBACK (render), NULL);
}

If you need to initialize OpenGL state, e.g. buffer objects or shaders, you should use the [gtk.widget.Widget.realize] signal; you can use the [gtk.widget.Widget.unrealize] signal to clean up. Since the [gdk.glcontext.GLContext] creation and initialization may fail, you will need to check for errors, using [gtk.glarea.GLArea.getError].

An example of how to safely initialize the GL state is:

static void
on_realize (GtkGLarea *area)
{
 // We need to make the context current if we want to
 // call GL API
 gtk_gl_area_make_current (area);

 // If there were errors during the initialization or
 // when trying to make the context current, this
 // function will return a GError for you to catch
 if (gtk_gl_area_get_error (area) != NULL)
   return;

 // You can also use gtk_gl_area_set_error() in order
 // to show eventual initialization errors on the
 // GtkGLArea widget itself
 GError *internal_error = NULL;
 init_buffer_objects (&error);
 if (error != NULL)
   {
     gtk_gl_area_set_error (area, error);
     g_error_free (error);
     return;
   }

 init_shaders (&error);
 if (error != NULL)
   {
     gtk_gl_area_set_error (area, error);
     g_error_free (error);
     return;
   }
}

If you need to change the options for creating the [gdk.glcontext.GLContext] you should use the signal@Gtk.GLArea::create-context signal.

Fluent builder for [gtk.glarea.GLArea]