Package org.gnome.gtk

Class GLArea

java.lang.Object
org.javagi.base.ProxyInstance
org.gnome.gobject.TypeInstance
org.gnome.gobject.GObject
org.gnome.gobject.InitiallyUnowned
org.gnome.gtk.Widget
org.gnome.gtk.GLArea
All Implemented Interfaces:
Accessible, Buildable, ConstraintTarget, Proxy
@Generated("io.github.jwharm.JavaGI") public class GLArea extends Widget implements Accessible, Buildable, ConstraintTarget
Allows drawing with OpenGL.

An example GtkGLArea

GtkGLArea sets up its own 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::render signal, or subclass GtkGLArea and override the GtkGLAreaClass.render virtual function.

The GtkGLArea widget ensures that the GdkGLContext 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 GtkGLArea is to create a widget instance and connect to the Gtk.GLArea::render signal:

The render() function will be called when the GtkGLArea 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 {@code 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);

   // record the active framebuffer ID, so we can return to it
   // with {@code glBindFramebuffer (GL_FRAMEBUFFER, screen_fb)} should
   // we, for instance, intend on utilizing the results of an
   // intermediate render texture pass
   GLuint screen_fb = 0;
   glGetIntegerv (GL_FRAMEBUFFER_BINDING, &screen_fb);

   // 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::realize signal; you can use the Gtk.Widget::unrealize signal to clean up. Since the GdkGLContext creation and initialization may fail, you will need to check for errors, using 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 GdkGLContext you should use the Gtk.GLArea::create-context signal.