GLArea
Object Hierarchy:
Description:
public class GLArea : Widget, Accessible, Buildable, ConstraintTarget
`GtkGLArea` is a widget that allows drawing with OpenGL.
`GtkGLArea` sets up its own [class@Gdk.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 [signal@Gtk.GLArea:GtkGLArea: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 [signal@Gtk.GLArea:
GtkGLArea: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.
```c 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 [signal@Gtk.Widget:GtkGLArea:realize]
signal; you can use the [signal@Gtk.Widget:GtkGLArea:unrealize] signal to clean up. Since the `GdkGLContext` creation and
initialization may fail, you will need to check for errors, using [method@Gtk.GLArea.get_error].
An example of how to safely initialize the GL state is:
```c 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 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 [signal@Gtk.GLArea:GtkGLArea:create-context]
signal.