GtkGLArea issues: context type, getProcAddress and key events

Platform
1

I’m replace native window with GtkGLArea, but there are some problems:

  1. how do i knows the type of gl context created by gtk, EGL or GLX?

  2. is there a api like eglGetProcAddress and glXGetProcAddress?

  3. gl area couldn’t receive key press/release events even if i add related event masks to the widget, test code is here:

#include <GL/gl.h>
#include <gtk/gtk.h>

static gboolean key_press(GtkGLArea *area, GdkEvent *event, gpointer data) {
  printf("key press: %d\n", ((GdkEventKey *)event)->keyval);
  return TRUE;
}

static gboolean key_release(GtkGLArea *area, GdkEvent *event, gpointer data) {
  printf("key release: %d\n", ((GdkEventKey *)event)->keyval);
  return TRUE;
}

static gboolean render(GtkGLArea *area, GdkGLContext *context, gpointer data) {
  printf("draw\n");
  GtkAllocation alloc;
  gtk_widget_get_allocation(GTK_WIDGET(area), &alloc);
  glViewport(0, 0, alloc.width, alloc.height);
  glClear(GL_COLOR_BUFFER_BIT);
  glClearColor(0.3, 0.3, 0.0, 1.0);
  glFlush();

  return TRUE;
}

int main(int argc, char **argv) {
  gtk_init(&argc, &argv);

  GtkWidget *window = gtk_window_new(GTK_WINDOW_TOPLEVEL),
            *gl_area = gtk_gl_area_new();
  gtk_widget_add_events(gl_area, GDK_KEY_PRESS_MASK | GDK_KEY_RELEASE_MASK);
  g_signal_connect(window, "delete-event", G_CALLBACK(gtk_main_quit), NULL);
  g_signal_connect(gl_area, "render", G_CALLBACK(render), NULL);
  g_signal_connect(gl_area, "key-press-event", G_CALLBACK(key_press), NULL);
  g_signal_connect(gl_area, "key-release-event", G_CALLBACK(key_release), NULL);

  gtk_container_add(GTK_CONTAINER(window), gl_area);
  gtk_widget_show_all(window);
  gtk_widget_grab_focus(GTK_WIDGET(gl_area)); 
  gtk_main();
  return 0;
}
``
2

i have solved problem 3: call gtk_widget_set_can_focus on the gl area widget.

1 Like
3

I believe the answer is: if you’re using X, its GLX, if you are using Wayland, it is EGL.

4

GTK uses libepoxy, so you can use the libepoxy API, like epoxy_has_glx(), epoxy_has_egl(), etc.

In general, GTK will create GLX contexts under X11, and EGL contexts under Wayland.

Use libepoxy.

To be fair, though, I have no idea what you’re trying to achieve. You should not ever know what kind of underlying windowing system API created a GL context; if you want to check for windowing system-specific extensions, you can use epoxy_has_glx_extension(), epoxy_has_egl_extension(), or epoxy_has_wgl_extension() before using them, just like you’d use epoxy_has_gl_extension().

5

@matthiasc @ebassi , i’m using a third party library to do opengl rendering, it requires a function likes eglGetProcAddress and glXGetProcAddress, so i wants a api such as gdk_gl_context_get_proc_address or a api to knows the context type.

I believe the answer is: if you’re using X, its GLX, if you are using Wayland, it is EGL.

thank you, this answer could solve my problem.

6

Sorry, we are not going to add that API to GDK: we have a hard dependency on libepoxy, and libepoxy already provides that API.

7

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