The weather was a bit of a puzzle to make. The basic idea is to make the world look brighter on a sunny day, and more grey on a clouded or rainy day.
The first requirement was of course the ability to lighten or darken the entire world view. It's like recolouring, but a) every pixel changes instead of only a few, and b) colours only get lighter or darker. The previous step of getting proper recolouring some months ago also solved the gradient shifting, so that was already available.
Interestingly, the more tricky part was deciding what weather should be displayed. In reality, weather "just happens". In a game, you have to program it. To program it, you need an algorithm to decide what weather should be displayed!
In the end I made a table for each month, how often each type of weather in that month occurs. Then by drawing a random number (uniform distribution over the sum of occurrences of all weather types), the 'new' weather is decided.
Immediately jumping to that new weather would be a bit weird however, you'd have sun one day, and thick rain the next. To make the transition more smooth, the change is done gradually in a few days.
The temperature is interpolated between the average temperatures of each month. This may be a bit too simplistic but it will do for now.
With the weather type and temperature decided, smoothly changing to new weather over a couple of days, and connecting the current weather to the gradient shifting, we have bright sunny days and dark cloudy days now as you can see in the pictures. Other effects of the weather still have to be programmed.
