gl: Make all user GdkGLContexts not attached to any window

We make user facing gl contexts not attached to a surface if possible,
or attached to dummy surfaces. This means nothing can accidentally
read/write to the toplevel back buffer.

gdk/wayland/gdkdisplay-wayland.h

@@ -89,6 +89,7 @@ struct _GdkWaylandDisplay
   guint have_egl_khr_create_context : 1;
   guint have_egl_buffer_age : 1;
   guint have_egl_swap_buffers_with_damage : 1;
+  guint have_egl_surfaceless_context : 1;
 };
 
 struct _GdkWaylandDisplayClass

gdk/wayland/gdkglcontext-wayland.c

@@ -76,7 +76,8 @@ gdk_wayland_window_invalidate_for_new_frame (GdkWindow      *window,
   egl_surface = gdk_wayland_window_get_egl_surface (window->impl_window,
                                                     context_wayland->egl_config);
 
-  if (display_wayland->have_egl_buffer_age)
+  if (display_wayland->have_egl_buffer_age &&
+      gdk_gl_context_make_current (window->gl_paint_context))
     eglQuerySurface (display_wayland->egl_display, egl_surface,
                      EGL_BUFFER_AGE_EXT, &buffer_age);
 
@@ -203,6 +204,9 @@ gdk_wayland_display_init_gl (GdkDisplay *display)
   display_wayland->have_egl_swap_buffers_with_damage =
     epoxy_has_egl_extension (dpy, "EGL_EXT_swap_buffers_with_damage");
 
+  display_wayland->have_egl_surfaceless_context =
+    epoxy_has_egl_extension (dpy, "EGL_KHR_surfaceless_context");
+
   GDK_NOTE (OPENGL,
             g_print ("EGL API version %d.%d found\n"
                      " - Vendor: %s\n"
@@ -297,6 +301,7 @@ find_eglconfig_for_window (GdkWindow        *window,
 
 GdkGLContext *
 gdk_wayland_window_create_gl_context (GdkWindow     *window,
+				      gboolean       attached,
                                       GdkGLProfile   profile,
                                       GdkGLContext  *share,
                                       GError       **error)
@@ -359,6 +364,7 @@ gdk_wayland_window_create_gl_context (GdkWindow     *window,
 
   context->egl_config = config;
   context->egl_context = ctx;
+  context->is_attached = attached;
 
   return GDK_GL_CONTEXT (context);
 }
@@ -404,7 +410,16 @@ gdk_wayland_display_make_gl_context_current (GdkDisplay   *display,
   context_wayland = GDK_WAYLAND_GL_CONTEXT (context);
   window = gdk_gl_context_get_window (context);
 
-  egl_surface = gdk_wayland_window_get_egl_surface (window->impl_window, context_wayland->egl_config);
+  if (context_wayland->is_attached)
+    egl_surface = gdk_wayland_window_get_egl_surface (window->impl_window, context_wayland->egl_config);
+  else
+    {
+      if (display_wayland->have_egl_surfaceless_context)
+	egl_surface = EGL_NO_SURFACE;
+      else
+	egl_surface = gdk_wayland_window_get_dummy_egl_surface (window->impl_window,
+								context_wayland->egl_config);
+    }
 
   if (!eglMakeCurrent(display_wayland->egl_display, egl_surface,
                       egl_surface, context_wayland->egl_context))

gdk/wayland/gdkglcontext-wayland.h

@@ -39,6 +39,7 @@ struct _GdkWaylandGLContext
 
   EGLContext egl_context;
   EGLConfig egl_config;
+  gboolean is_attached;
 };
 
 struct _GdkWaylandGLContextClass
@@ -48,6 +49,7 @@ struct _GdkWaylandGLContextClass
 
 gboolean        gdk_wayland_display_init_gl                         (GdkDisplay        *display);
 GdkGLContext *  gdk_wayland_window_create_gl_context                (GdkWindow         *window,
+								     gboolean           attach,
                                                                      GdkGLProfile       profile,
                                                                      GdkGLContext      *share,
                                                                      GError           **error);

gdk/wayland/gdkprivate-wayland.h

@@ -239,5 +239,7 @@ void gdk_wayland_selection_unset_data_source (GdkAtom selection);
 
 EGLSurface gdk_wayland_window_get_egl_surface (GdkWindow *window,
                                                EGLConfig config);
+EGLSurface gdk_wayland_window_get_dummy_egl_surface (GdkWindow *window,
+						     EGLConfig config);
 
 #endif /* __GDK_PRIVATE_WAYLAND_H__ */

gdk/wayland/gdkwindow-wayland.c

@@ -101,6 +101,9 @@ struct _GdkWindowImplWayland
   struct wl_egl_window *egl_window;
   EGLSurface egl_surface;
 
+  struct wl_egl_window *dummy_egl_window;
+  EGLSurface dummy_egl_surface;
+
   unsigned int mapped : 1;
   unsigned int use_custom_surface : 1;
   unsigned int pending_commit : 1;
@@ -1171,6 +1174,18 @@ gdk_wayland_window_hide_surface (GdkWindow *window)
 
   if (impl->surface)
     {
+      if (impl->dummy_egl_surface)
+        {
+          eglDestroySurface(display_wayland->egl_display, impl->dummy_egl_surface);
+          impl->dummy_egl_surface = NULL;
+        }
+
+      if (impl->dummy_egl_window)
+        {
+          wl_egl_window_destroy (impl->dummy_egl_window);
+          impl->dummy_egl_window = NULL;
+        }
+
       if (impl->egl_surface)
         {
           eglDestroySurface(display_wayland->egl_display, impl->egl_surface);
@@ -2238,6 +2253,32 @@ gdk_wayland_window_get_egl_surface (GdkWindow *window,
   return impl->egl_surface;
 }
 
+EGLSurface
+gdk_wayland_window_get_dummy_egl_surface (GdkWindow *window,
+					  EGLConfig config)
+{
+  GdkWaylandDisplay *display_wayland = GDK_WAYLAND_DISPLAY (gdk_window_get_display (window));
+  GdkWindowImplWayland *impl;
+  struct wl_egl_window *egl_window;
+
+  g_return_val_if_fail (GDK_IS_WAYLAND_WINDOW (window), NULL);
+
+  impl = GDK_WINDOW_IMPL_WAYLAND (window->impl);
+
+  if (impl->dummy_egl_surface == NULL)
+    {
+      impl->dummy_egl_window =
+        wl_egl_window_create (impl->surface, 1, 1);
+
+      impl->dummy_egl_surface =
+        eglCreateWindowSurface (display_wayland->egl_display,
+                                config, impl->dummy_egl_window, NULL);
+    }
+
+  return impl->dummy_egl_surface;
+}
+
+
 /**
  * gdk_wayland_window_set_use_custom_surface:
  * @window: (type GdkWaylandWindow): a #GdkWindow