"This is a time and weather system. It does not use standard time, but rather morning, midday, afternoon, evening, night. The weather changes over time, as well as the clouds, wind, rain, and be sure to check out the sun."
I always liked being able to simulate things and this demo does a good job of showing how you could make something similar for your games. This setup is easily adaptable to simulate a large number of environmental things.
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