Mine

        execute_context(CONTEXT_TERRAIN); //draw some things        get_backbuffer(&backbuffer);        backbuffer.writeToTIFF("terrain.tif"); //write backbuffer to a file        glClearColor(0.0,0.0,0.0,0.0);        glClear(GL_COLOR_BUFFER_BIT);        glFlush();        execute_context(CONTEXT_SYMBOLS); //draw some other things        get_backbuffer(&backbuffer);        backbuffer.writeToTIFF("annotaions.tif"); //write backbuffer to a file