Add is_valid() to egl/glx context

engine/renderers/gl/egl/GLContext.cpp

@@ -90,6 +90,8 @@ void GLContext::destroy_context()
  	eglDestroyContext(display, context);
  	eglDestroySurface(display, surface);
  	eglTerminate(display);
+
+    display = EGL_NO_DISPLAY;
 }
 
 //-----------------------------------------------------------------------------

engine/renderers/gl/egl/GLContext.h

@@ -44,6 +44,11 @@ public:
 
 	void			swap_buffers();
 
+	void is_valid()
+	{
+		return display != EGL_NO_DISPLAY;
+	}
+
 private:
 
 	EGLDisplay 		display;

engine/renderers/gl/glx/GLContext.cpp

@@ -42,7 +42,7 @@ void set_x11_display_and_window(Display* dpy, Window win)
 
 //-----------------------------------------------------------------------------
 GLContext::GLContext() :
-	m_glx_context(NULL)
+	m_glx_context(None)
 {
 }
 
@@ -91,6 +91,8 @@ void GLContext::destroy_context()
 			glXDestroyContext(s_x11_display, m_glx_context);
 		}
 	}
+
+	m_glx_context = None;
 }
 
 //-----------------------------------------------------------------------------

engine/renderers/gl/glx/GLContext.h

@@ -46,9 +46,14 @@ public:
 
 	void			swap_buffers();
 
+	bool is_valid()
+	{
+		return m_glx_context != None;
+	}
+
 private:
 
-	GLXContext		m_glx_context;
+	GLXContext m_glx_context;
 };
 
 } // namespace crown