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dev:weather

Guide to basic crossfire weather system

Due to a number of reasons (code complexity, original developer no longer involved with the project, lack of use, etc.) the weather feature was officially removed from Crossfire in Feb-2008. This page is still available for those who wish to run, or are running versions of Crossfire that still use this feature. This page is considered deprecated.

How do I turn on the weather?

In your settings file, there are a few parameters that affect weather. To turn on weather, you must turn on the worldmap* settings. Simply uncomment them, and leave them as the defaults. Second, you want to set dynamiclevel to something you are happy with:

Dynamiclevel Meaning
0 No weather.
1 Weather happens, players are affected, but there are no visual cues.
2 Weather creates visual effects on the map, like puddles, rain, fog, etc.
3 Weather creates items on the map, like herbs, flowers, apples in trees, etc. Possibly trees defoliate in the winter, etc.
4 Rivers and lakes will appear as a product of rainfall, snow melt.
5 The map will be entirely dynamic. Trees and deserts will appear depending on the weather conditions in those areas.

When you first start the weather system, it will generate all the basic maps for the weather. These maps are located in your var directory. Each map will contain data for the world on things like elevation, humidity, sky conditions, temperature, etc. The initial generation of the elevation, water and humidity maps takes about 30 minutes on a fast machine. You will only have to suffer through this once, unless you delete one of those maps. If you delete one, it is advised to delete all three of those, as they are generated in one pass. If you feel some part of the weather has gone out of control, you can delete the maps at any time, and regenerate them at startup.

As the game sits idle, it will slowly process the worldmap, adding weather. For a newly started server, this can lead to blockiness in the weather. It is advised that you set the fastclock setting to 1, and run the game for an hour or two (without players), to let the weather smooth out. As it runs, it will depost overlay maps of the world in var/maps/world. When you have 900 of these, it has made one pass. It's not advised to run the game in fastclock mode normally.

If you want to see the weather visually, compile the “maps” program in the utils directory. (gcc -o maps maps.c). Go to your var directory, and run it there. It will process your *map files, and generate ppm's you can look at, to see the weather formations.

How does the weather work?

There are two types of things in the weather system. Computed values, and random values.

Pressure is the only random value.

The world is divided into a 100×100 grid of “weathermap squares” (WM). Each square is computed every game hour.

The game computes humidity by looking at the amount of water in the current WM. It then compares the pressure of nearby squares, to compute wind direction and speed. Humidity is pushed to nearby squares, via the wind. The temperature is mostly static, but is computed by the distance from the poles (NW and SE corners of the map) and the current season. In addition, the elevation of the area is taken into effect, as is windspeed. The equator moves up and down the map, as the seasons change, to simulate a reverse season for north and south hemispheres.

Once the game has all of these values, it compares them against eachother, and computes the sky conditions for the current WM. After computing the sky conditions, the game then performs the actual changes (if any) to the maps.

Changes to the map occur under two conditions: 1) The map was entered by a player. 2) The game loads and saves 1 tile per game hour, slowly moving across the world.

I want to make a special snow to cover "some arch"

Look at the table at the beginning of weather.c. Add your special snow, and the name of the arch to that table. Also, add your snowtype to the avoidance table, to allow it to melt, and avoid the game double-stacking the snow on your square.

Can we make spells to affect weather?

Yes. But remember that the game is constantly recalculating the weather. If you want something that will affect an area of the world for a long period of time, you will need to modify the weather code to special case that. Temperature, for example, is constantly recalculated, your spell will only work for 1 game hour.

That being said.. some amount of player fiddling can be done without special code. For example, if you were to crank the pressure of a WM square up really high, and put the humidity of that square at 100%, over a few game hours, that square would essentially become the eye of a storm, as the wind would pick up moving outwards from it, spreading the humidity. Eventually, the game will flatten it out on it's own, but there will be a lingering effect for many hours to come. Feel free to experiment with such things.

Things that are recalculated:

  • temperature
  • sky conditions

Things that are smoothed/spread:

  • humidity
  • pressure
  • wind

I advise that you do not mess with the elevation or water maps, as those are not recalculated over time. If you change the water % of a WM square, and don't put it back, it will stay that way until the server admin deletes the watermap and regenerates.

dev/weather.txt · Last modified: 2010/06/24 14:14 (external edit)