This's an extract from this post (The reason why it was posted there is because the first set of pool-tiles and pool-wallpapers are for the Simstone project, so the original posts were inaccessible to the public. As the project has been released, I re-posted these infos out here. The contents are all the same. So, for most users, no need to visit that linked post. It's just only for references.)
It's about how pool-tiles and pool-wallpapers (caustic tiles and caustic wallpapers) can be made on HCP products.



The vision:
The swim-pool are graphically made up of the following things:
1. pool walls (for bounding limits on sims accessment)
2. pool tiles (for underwater animation, known as caustic effects)
3. poolwallpapers (for underwater animation, known as caustic effects)
4. poolsheet object (for water splashes, especilly sims using for the diving board)
5. pool surface tile (for water surface animation, for the wavy effect)

The pool animaions are done through 2, 3, 4, 5 but not 1.
The swimming animations are done through pool accessories like ladders and diving-boards.

What the pool tiles and wallpapers do is to simulate the wavy pattern under the water while the pool surface tiles is to simulate the water surface... and the blue layer sheets are pool-depth tiles from the base game are to simulate different levels of colour change in terms of the game depth.
So far, with my limited skills and knowledge, I can only get the pool tiles and wallpapers to work on HCP products by using settings from the original pool tiles and wallpapers... while using different guid IDs from HCP products. In other words, these files are kinda hybrids of the original and HCP custom clones.

Only a few settings may need changes (so, it's very simple):

0. XXYY = pool-tile settings/pool-wallpaper settings
1. txmt type = floorpool/WallpaperPool
2. properties: floorCausticsPass=1/tsCausticsPass=1

Non-essential properties: (for pool-wallpapers)

stdMatSpecCoef=0.025,0.025,0.025
stdMatSpecPower=2


Here's a more step-by-step description:
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it's very easy to turn normal HCP tiles and wallpapers into their pool versions... with simpe, just open them in simpe. There'll be a txmt file, a txtr file, a xml file in each of them.

1. At the txmt file, just go to the cMaterialDefinition menu, change the
a. (for the wallpaper) wallpaperbump -> WallpaperPool
b. (for the tile) floor -> FloorPool

2. still at the txmt file, go to the properties menu, click "add" and move to the bottom to click on the newly added line, then add the followings accordingly.
a. (for the wallpaper) tsCausticsPass : 1
b. (for the tile) floorCausticsPass : 1

3. Then, click "sort list" to resort the property lines. ( this is to ensure all the lines to be read properly.) and then, click commit and save the files. The sequences are important.

Done, just import the new graphic, reuse the texture you're already prepared with HCP, or whatever you like.
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Limitation: (The golden rule of the game so far)
1. One has to have at least a block of swim-pool in the game screen somewhere in order to activate the animation though. If that swim-pool block is out of the screen's scope or there's no swim-pool block, these pool-tiles or pool-wallpapers won't be animated...
The pool block can be hidden under some foundation or else in order to mak ungrounded pools on higher levells..
2. ***Update 31st August, 2006*** ()This's still for testing...()
Some invisible recolours with "CausticsGeneratorMaterial" as the txmt type can activate the caustic animation. A bit more info about this mod here See the attched example "Numenor(MTS2)_SphereMatte_Moi_sphere_023-CausticsGeneratorMaterial". Just place it somewhere on the pool-tiles (caustic tiles) inside the pool. For the invisible sphere with the generator to show up, you'll need
Maxis "Lost & Found" #4: The Matte Sphere *OPEN CONTEST* by Numenor
http://www.modthesims2.com/showthread.php?t=36604
Also, the file "Numenor(MTS2)_SphereMatte_Moi_stand_GS-nil" is an invisible recolour for the stand.
Or if you feel like to find a better way to solve this limitation, go ahead, I'm completely happy with that.

They've been tested to work in all EPs, HCP and SP up to now.

If wanna try an example to see how, download the attachments.


***Update 21st Aug, 2006***
The pool-set for the pool-tiles and pool-wallpapers is here
They all borrow txtr from their correponding normal host tiles & wallpapaers you can download here
So, you'll need the wallpaper & tile pack there in order for them to show up properly.

The attached is an example for the fake-pool approach.
The linked "Stonesims_Cs001_SimstoneCentre.rar " is an instance for re-wallpapering the swim-pool.

For other infos, may check out this post
To read about swim-pool modding, may read here