Struct gtk4::GLArea

source ·
#[repr(transparent)]
pub struct GLArea { /* private fields */ }
Expand description

GLArea is a widget that allows drawing with OpenGL.

An example GtkGLArea

GLArea sets up its own 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.

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

The GLArea widget ensures that the gdk::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 signal::GLArea::render signal:

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

⚠️ The following code is in 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::Widget::realize signal; you can use the signal::Widget::unrealize signal to clean up. Since the gdk::GLContext creation and initialization may fail, you will need to check for errors, using GLAreaExt::error().

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

⚠️ The following code is in 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 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 you should use the signal::GLArea::create-context signal.

Implements

GLAreaExt, WidgetExt, glib::ObjectExt, AccessibleExt, BuildableExt, ConstraintTargetExt, WidgetExtManual, AccessibleExtManual

Implementations§

Creates a new GLArea widget.

Returns

a new GLArea

Creates a new builder-pattern struct instance to construct GLArea objects.

This method returns an instance of GLAreaBuilder which can be used to create GLArea objects.

Trait Implementations§

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