Particle effects : snow and rain
  by Nicolas VIVIEN
===================================================
							Patch v3 (only test)


FEATURES :
----------
This first try permits to add a basic snow and rain effects in using
particle from OSG.

For the moment, the patch uses the METAR informations to enable / disable
rain or snow effects. (intensity of effects is : low, meddium, high)


CHANGELOG v3 :
--------------
- The origin of Precipitation object is calculate with worldcoordinate Matrix.
- Precipitations fall vertically anywhere on the earth...


CHANGELOG v2 :
--------------
- Link the precipitation object to tile element :
Now, there is one precipitation object per tile. It permits to use the world coordinate.
- Add links between precipitation and cloud layers :
When you are above the cloud layer, the precipitations are stopped.


CHANGELOG v1 :
--------------
Firt step : test the precipitation effect.


TO DO :
-------
For the next release of patch :
1) Add the wind direction and velocity effect
2) it's raining cats and dogs in my plane !!! (fixed this issue)
3) I want to the density of effects depend on altitude. If I'm higher than 
clouds layer, rain (or snow) is stopped...
4) The particle effects have to depend on the camera position.


INSTALL :
---------

- You have to remove the others patch about precipitation.

- You have to add the two files :
precipitation.hxx and precipitation.cxx 
in the directory simgear/simgear/environment

- You have to apply simgear patch

- You have to add the two files :
precipitation_mgr.hxx and precipitation_mgr.cxx 
in the directory flightgear/src/Environment

- You have to apply flightgear patch

- Then, build simgear and flightgear.

