Precipitations Tutorial

Seeing that lots of people have had some problems with putting rain, snow, etc in their games i'm writing this little tutorial that will help you do all the modifications you need.

First of all let's create a new script file called precipitations or something ... (ie. fps/server/scripts/precipitations.cs). In that file we need to declare the precipitation data blocks, like this:

datablock PrecipitationData(Rain)
{
type = 1;
materialList = "~/data/specialfx/raindrops.dml";
sizeX = 0.10;
sizeY = 0.10;

movingBoxPer = 0.35;
divHeightVal = 1.5;
sizeBigBox = 1;
topBoxSpeed = 20;
frontBoxSpeed = 30;
topBoxDrawPer = 0.5;
bottomDrawHeight = 40;
skipIfPer = -0.3;
bottomSpeedPer = 1.0;
frontSpeedPer = 1.5;
frontRadiusPer = 0.5;
};
//-------------------- SNOW -----------------------------------------------------
datablock PrecipitationData(Snow)
{
type = 1;
materialList = "~/data/specialfx/snowflakes.dml";
sizeX = 0.10;
sizeY = 0.10;

movingBoxPer = 0.35;
divHeightVal = 1.5;
sizeBigBox = 1;
topBoxSpeed = 20;
frontBoxSpeed = 30;
topBoxDrawPer = 0.5;
bottomDrawHeight = 40;
skipIfPer = -0.3;
bottomSpeedPer = 1.0;
frontSpeedPer = 1.5;
frontRadiusPer = 0.5;
};

Now we need to load this file, open up game.cs and add the following line where similar lines are (ie, after the exec("./player.cs"); line should be ok):

exec("./precipitations.cs");

That will declare two datablocks for us to use in our missions, rain and snow. Notice the materialList line... its pointing to a .dml file, we have to create this file which is just a simple text file that points to the textures we want to use. For our example we will put the textures in the same dir as the dml file. So go ahead, open up notepad, vim or your editor of choice and make a file that contains the name of the textures you are gonna use, for example if you have only one texture called raindrops.png in the same dir as the .dml file you would put this:

raindrops

If you have several textures you just add the names of the textures, for example:

raindrop1
raindrop2
raindrop3

You should press ENTER after you type raindrops so that you create a blank line below it.. this IS IMPORTANT. Now save that file as ~/data/specialfx/raindrops.dml
Create another file but this time add (i you have a snowflakes.png):

snowflakes

Dont forget the ENTER please! Save this one as ~/data/specialfx/snowflakes.dml

Now open up the mission file (.mis) in which you want to add the rain or snow and add something like this (change the datablock if you want to):

new Precipitation(Precipitation) {
position = "0 0 0";
rotation = "1 0 0 0";
scale = "1 1 1";
dataBlock = "Rain";
percentage = "1";
color1 = "1.000000 1.000000 1.000000 1.000000";
color2 = "-1.000000 0.000000 0.000000 1.000000";
color3 = "-1.000000 0.000000 0.000000 1.000000";
offsetSpeed = "0.25";
minVelocity = "1.5";
maxVelocity = "3.5";
maxNumDrops = "2000";
maxRadius = "100";
locked = "true";
};

Now we need to do some engine source code changes...

open up game/fx/precipitation.cc
and find the function "void Precipitation::loadDml()"
just after the opening brace of this function (the very top) add this code:

//Added code
char path[1024], *p;
dStrcpy( path, mDataBlock->mMaterialListName );
if( (p = dStrrchr( path, '/')) != NULL )
*p = 0;

Now a few lines after that you should see a line like this one:

mMaterialList.load();

change it to look like this

mMaterialList.load(path);

Ok now you need to make a decision. You can make your precipitation textures in 2 ways. The first one and default one includes 9 different drops or flakes in 1 texture (only one .png file for 9 drops or flakes). The other way round you need to modify some engine code so that you would be able to have each flake/drop in a different file. Personally i left it as it was and used a texture i got from tribes 2 :)
If you want to use each raindrop or snowflake in a different file do this:
In precipitation.cc look for a line that looks like this: glTexCoord2f(coordX, coordY); and change all the glTexCoord2f lines to look like in the code below (in the code below the old glTexCoord where commented out and the new ones where typed below). The only thing that changes is that instead of being passed a coordX and a coordY the texture coordinates are set to 0 and 0. This way you would use each texture completely for each flake/drop.

// glTexCoord2f(coordX, coordY);
glTexCoord2f(0, 0);
glVertex3f(point[0].x, point[0].y, point[0].z);
// glTexCoord2f(coordX, coordY + 0.25);
glTexCoord2f(0, 1.0);
glVertex3f(point[1].x, point[1].y, point[1].z);
// glTexCoord2f(coordX + 0.25, coordY + 0.25);
glTexCoord2f(1.0, 1.0);
glVertex3f(point[2].x, point[2].y, point[2].z);
// glTexCoord2f(coordX + 0.25, coordY);
glTexCoord2f(1.0, 0);
glVertex3f(point[3].x, point[3].y, point[3].z);

Well now you have to create you snowflake and raindrop texture(s). If you left the code unchanged you'll have to make a texture with 9 flakes in it. I dont have much information on how to create this texture since i used a tribes 2 one. I found it in the special dir in tribes2. If you dont have tribes 2 email me and ill give you a hand with creating this 9x9 textures.
Otherwise you'll have to create each flake or drop in a separate file which is easier. The images should have an alpha channel for the background. Well that's all, hope you enjoy your new weather :)
If there's any bug in this tutorial please e-mail me asap and ill fix it!
Well enjoy, and wait for my character selection tutorial :)

PD: Special thanks go to SnowMan which told me about the needed engine changes :)
Thanks a lot man!