OPENGL: Add notification function about context destruction.

backends/graphics/opengl/opengl-graphics.cpp

@@ -881,6 +881,26 @@ void OpenGLGraphicsManager::notifyContextChange(const Graphics::PixelFormat &def
 #endif
 }
 
+void OpenGLGraphicsManager::notifyContextDestroy() {
+	if (_gameScreen) {
+		_gameScreen->releaseInternalTexture();
+	}
+
+	if (_overlay) {
+		_overlay->releaseInternalTexture();
+	}
+
+	if (_cursor) {
+		_cursor->releaseInternalTexture();
+	}
+
+#ifdef USE_OSD
+	if (_osd) {
+		_osd->releaseInternalTexture();
+	}
+#endif
+}
+
 void OpenGLGraphicsManager::adjustMousePosition(int16 &x, int16 &y) {
 	if (_overlayVisible) {
 		// It might be confusing that we actually have to handle something

backends/graphics/opengl/opengl-graphics.h

@@ -136,6 +136,14 @@ protected:
 	 */
 	void notifyContextChange(const Graphics::PixelFormat &defaultFormat, const Graphics::PixelFormat &defaultFormatAlpha);
 
+	/**
+	 * Notify the manager that the OpenGL context is about to be destroyed.
+	 * This will free up/reset internal OpenGL related state and *must* be
+	 * called whenever a context might be created again after destroying a
+	 * context.
+	 */
+	void notifyContextDestroy();
+
 	/**
 	 * Adjust the physical mouse coordinates according to the currently visible screen.
 	 */