public void drawPlane() {
            if(!init) {
                init = true;
                centerX = getWidth() / 2;
                centerY = getHeight() / 2;
            }
            int width = getWidth();
            int height = getHeight();
            for(int i = centerX % pixelUnit; i < width; i += pixelUnit) {
                if(i < 0) i += pixelUnit;
                for(int j = 0; j < height; j++) {
                    canvas.setRGB(i, j, Color.GRAY.getRGB());
                }
            }
            for(int i = centerY % pixelUnit; i < height; i += pixelUnit) {
                if(i < 0) i += pixelUnit;
                for(int j = 0; j < width; j++) {
                    canvas.setRGB(j, i, Color.GRAY.getRGB());
                }
            }
        }