public void update(double deltaTime) {
		for (Entry<GameObject, Sprite> entry : spriteCache.entrySet()) {
			entry.getKey().update(deltaTime);
			entry.getValue().update(deltaTime);
		}

		if (LOGGER.isInfoEnabled()) {
			// update FPS counter every half a second
			secondsSinceLastFPSUpdate += deltaTime;
			numFramesSinceLastFPSUpdate++;
			if (secondsSinceLastFPSUpdate >= 0.5f) {
				oldFPS = Math.round(numFramesSinceLastFPSUpdate / secondsSinceLastFPSUpdate);
				secondsSinceLastFPSUpdate = 0;
				numFramesSinceLastFPSUpdate = 0;
			}
		}
	}