public void setDimensions(int width, int height) {
		if (width <= 0 || height <= 0) {
			throw new IllegalArgumentException("viewport dimensions must be greater zero");			
		}
		this.width = width;
		this.height = height;
		this.halfWidth = this.width / 2.0;
		this.halfHeight = this.height / 2.0;
	}