GLArea
Object Hierarchy:
Description:
[ Version ( since = "3.16" ) ]
public class GLArea : Widget, Implementor, Buildable
GLArea is a widget that allows drawing with OpenGL.
GLArea sets up its own GLContext for the window it creates, 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.
In order to draw, you have to connect to the render signal, or subclass
GLArea and override the GtkGLAreaClass.render() virtual function.
The GLArea widget ensures that the 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 GLArea is to create a widget instance and connect to the render signal:
// 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);The `render()` function will be called when the GLArea is ready for you to draw its content:
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;
}If you need to initialize OpenGL state, e.g. buffer objects or shaders, you should use the realize signal; you can use the unrealize signal to clean up. Since the GLContext creation and initialization may fail, you will need to check for errors, using get_error. 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 GLContext you should use the create_context signal.