gdk: Add private GLContext::is_current() check

... and use this check in gdk_gl_context_make_current() and
gdk_gl_context_get_current() to make sure the context really is still
current.

The context no longer being current can happen when external GL
implementations make their own contexts current in the same threads GDK
contexts are used in.
And that can happen for example by WebKit.

Theoretically, this should also allow external EGL code to run in X11
applications when GDK chooses to use GLX, but I didn't try it.

Fixes #5392

gdk/gdkglcontext.c

@@ -501,6 +501,18 @@ gdk_gl_context_real_is_shared (GdkGLContext *self,
   return TRUE;
 }
 
+static gboolean
+gdk_gl_context_real_is_current (GdkGLContext *self)
+{
+#ifdef HAVE_EGL
+  GdkGLContextPrivate *priv = gdk_gl_context_get_instance_private (self);
+
+  return priv->egl_context == eglGetCurrentContext ();
+#else
+  return TRUE;
+#endif
+}
+
 static gboolean
 gdk_gl_context_real_clear_current (GdkGLContext *context)
 {
@@ -670,6 +682,7 @@ gdk_gl_context_class_init (GdkGLContextClass *klass)
   klass->is_shared = gdk_gl_context_real_is_shared;
   klass->make_current = gdk_gl_context_real_make_current;
   klass->clear_current = gdk_gl_context_real_clear_current;
+  klass->is_current = gdk_gl_context_real_is_current;
   klass->get_default_framebuffer = gdk_gl_context_real_get_default_framebuffer;
 
   draw_context_class->begin_frame = gdk_gl_context_real_begin_frame;
@@ -1551,6 +1564,12 @@ gdk_gl_context_check_extensions (GdkGLContext *context)
   priv->extensions_checked = TRUE;
 }
 
+static gboolean
+gdk_gl_context_check_is_current (GdkGLContext *context)
+{
+  return GDK_GL_CONTEXT_GET_CLASS (context)->is_current (context);
+}
+
 /**
  * gdk_gl_context_make_current:
  * @context: a `GdkGLContext`
@@ -1569,7 +1588,7 @@ gdk_gl_context_make_current (GdkGLContext *context)
   masked_context = mask_context (context, surfaceless);
 
   current = g_private_get (&thread_current_context);
-  if (current == masked_context)
+  if (current == masked_context && gdk_gl_context_check_is_current (context))
     return;
 
   /* we need to realize the GdkGLContext if it wasn't explicitly realized */
@@ -1740,10 +1759,18 @@ GdkGLContext *
 gdk_gl_context_get_current (void)
 {
   MaskedContext *current;
+  GdkGLContext *context;
 
   current = g_private_get (&thread_current_context);
+  context = unmask_context (current);
 
-  return unmask_context (current);
+  if (context && !gdk_gl_context_check_is_current (context))
+    {
+      g_private_replace (&thread_current_context, NULL);
+      context = NULL;
+    }
+
+  return context;
 }
 
 gboolean

gdk/gdkglcontextprivate.h

@@ -83,6 +83,7 @@ struct _GdkGLContextClass
   gboolean              (* make_current)                        (GdkGLContext          *context,
                                                                  gboolean               surfaceless);
   gboolean              (* clear_current)                       (GdkGLContext          *context);
+  gboolean              (* is_current)                          (GdkGLContext          *context);
   cairo_region_t *      (* get_damage)                          (GdkGLContext          *context);
 
   gboolean              (* is_shared)                           (GdkGLContext          *self,

gdk/macos/gdkmacosglcontext.c

@@ -548,6 +548,14 @@ gdk_macos_gl_context_clear_current (GdkGLContext *context)
   return TRUE;
 }
 
+static gboolean
+gdk_macos_gl_context_is_current (GdkGLContext *context)
+{
+  GdkMacosGLContext *self = GDK_MACOS_GL_CONTEXT (context);
+
+  return self->cgl_context == CGLGetCurrentContext ();
+}
+
 static gboolean
 gdk_macos_gl_context_make_current (GdkGLContext *context,
                                    gboolean      surfaceless)
@@ -639,6 +647,7 @@ gdk_macos_gl_context_class_init (GdkMacosGLContextClass *klass)
 
   gl_class->get_damage = gdk_macos_gl_context_get_damage;
   gl_class->clear_current = gdk_macos_gl_context_clear_current;
+  gl_class->is_current = gdk_macos_gl_context_is_current;
   gl_class->make_current = gdk_macos_gl_context_make_current;
   gl_class->realize = gdk_macos_gl_context_real_realize;
   gl_class->get_default_framebuffer = gdk_macos_gl_context_get_default_framebuffer;

gdk/win32/gdkglcontext-win32-wgl.c

@@ -631,6 +631,14 @@ gdk_win32_gl_context_wgl_clear_current (GdkGLContext *context)
   return wglMakeCurrent (NULL, NULL);
 }
 
+static gboolean
+gdk_win32_gl_context_wgl_is_current (GdkGLContext *context)
+{
+  GdkWin32GLContextWGL *self = GDK_WIN32_GL_CONTEXT_WGL (context);
+
+  return self->wgl_context == wglGetCurrentContext ();
+}
+
 static gboolean
 gdk_win32_gl_context_wgl_make_current (GdkGLContext *context,
                                        gboolean      surfaceless)
@@ -682,6 +690,7 @@ gdk_win32_gl_context_wgl_class_init (GdkWin32GLContextWGLClass *klass)
   context_class->realize = gdk_win32_gl_context_wgl_realize;
   context_class->make_current = gdk_win32_gl_context_wgl_make_current;
   context_class->clear_current = gdk_win32_gl_context_wgl_clear_current;
+  context_class->is_current = gdk_win32_gl_context_wgl_is_current;
 
   draw_context_class->begin_frame = gdk_win32_gl_context_wgl_begin_frame;
   draw_context_class->end_frame = gdk_win32_gl_context_wgl_end_frame;

gdk/x11/gdkglcontext-glx.c

@@ -210,6 +210,14 @@ gdk_x11_gl_context_glx_clear_current (GdkGLContext *context)
   return TRUE;
 }
 
+static gboolean
+gdk_x11_gl_context_glx_is_current (GdkGLContext *context)
+{
+  GdkX11GLContextGLX *self = GDK_X11_GL_CONTEXT_GLX (context);
+
+  return self->glx_context == glXGetCurrentContext ();
+}
+
 static gboolean
 gdk_x11_gl_context_glx_make_current (GdkGLContext *context,
                                      gboolean      surfaceless)
@@ -685,6 +693,7 @@ gdk_x11_gl_context_glx_class_init (GdkX11GLContextGLXClass *klass)
   context_class->realize = gdk_x11_gl_context_glx_realize;
   context_class->make_current = gdk_x11_gl_context_glx_make_current;
   context_class->clear_current = gdk_x11_gl_context_glx_clear_current;
+  context_class->is_current = gdk_x11_gl_context_glx_is_current;
   context_class->get_damage = gdk_x11_gl_context_glx_get_damage;
 
   draw_context_class->end_frame = gdk_x11_gl_context_glx_end_frame;