@Override
        public Graphics getGraphics() {
            Graphics graphics = super.getGraphics();
            if (graphics instanceof Graphics2D) {
                return new NonClearGraphics2D((Graphics2D) graphics);
            }
            return new NonClearGraphics(graphics);
        }
Returns Graphics object that ignores {@link java.awt.Graphics#clearRect(int, int, int, int)}
calls.
<p>
This is done so that the frame buffer will not be cleared by AWT/Swing internals.

@see org.lwjgl.awthacks.NonClearGraphics2D
@see org.lwjgl.awthacks.NonClearGraphics
@return Graphics
jme3-lwjgl3/src/main/java/com/jme3/system/lwjgl/LwjglCanvas.java