See the Weather Tab of the Environment Panel for our default rain implementation, but we'll be dealing with the FX Trigger tab in the Environment Panel.
A to Z Walkthrough for Creating New Weather Systems:
The Emitter and the Particle Settings:
1. Make a particle effect chain to simulate let's say snow, and we'll call it SnowWeatherParticle.
2. On the SnowWeatherParticle tab increase the emitter radius to something large enough to surround the player, like (3,3,3).
3. Setup your particle like any other particle, but so that it looks like what you want it to for weather, ie, falling snow.
4. You can set the distance scale adjustment in the SnowWeatherParticle_p tab to something like -0.1, this will cause particles to get even larger as your character approaches them.
5. Enable viewing of emitters, now walk your character inside the emitter radius to check that the particles looks like what you would want your weather to look like.
6. On the the SnowWeatherParticle tab, change LinkToCamera from false to true. Now you'll most likely see that the emitter has jumped out in front of your camera, and that's because it's now using the emitter instance tab's location value as an offset from the camera position. So if you want the character to be surrounded by the particles, then set the location to be (0,0,0)
7. Copy the file location of the SnowWeatherParticle (not the SnowWeatherParticle_p).
The FX Spec:
1. Hit F5 to open the tools menu
2. Tab to Tools
3. FX System
4. Add a new FX spec, let's call it SnowFX, and edit it.
5. Drag a particle onto the FX group and select it, and past the file location you copied from SnowWeatherParticle into the event path. That's all you need to do for the particle.
6. Select the FX group and set it to:
7. Save the FX.
1. You can either make a new scheme, or add your weather to an existing scheme. The FX Triggers allow you to add any number and control whether your specific FX will show up based on the blend range of the env schemes currently being used in the area. But that's not important right now.
2. Edit the currently active environment scheme, click the FX trigger tab, click add, this will bring up the FX selection window, select SnowFX, and done.
See it in Action:
1. Load a new play instance of the area you are in, and you should now see your SnowWeatherParticle filling the screen. As your character runs around it will appear that the snow is everywhere.
The Advanced Stuff:
1. You can see more about the FX Triggers on the wiki, but for changing weather on the fly, your scripters can change blend values over time between various environment schemes using an external function, so you could have 5 identical environment schemes called snow, dust, rain, glowbugs, whatever, and have them all look the same, except their FX Triggers, so as the blend values change your 1 area could go from rain, then both rain and snow, then to just snow, etc.