View Full Version : Skinning From The Inside Out

31st Jul 2005, 12:34 AM
Just finished a new tutorial. Let me know if you see any mistakes or room for improvement, please?

Before you start skinning, itís helpful to understand how all the components of a sim go together. Iíll be focusing on sims, but many of the concepts here apply equally to objects. Letís start from the beginning. This is a picture of a skeleton in Maya, a 3D animation program. All sims have these skeletons Ė they are used to drive the animations. The sims themselves have different sizes, obviously, and depending on the skeleton size, the object animations will be different sometimes, as well. And while the skeletons are the same size for Young Adult, Adult, and Elder, the animations associated with them are different (just watch they way they walk!) No matter what you do to the outside, the skeleton isnít going to change Ė even if you stretch skeleton. Straaaaange things will happen!

Here is our model, Simthia. Sheís going to essentially stand here in various states of doneness to illustrate the layers of sim that are over the skeleton. Each one has different properties and reasons for being, and itís important to know how they work together. http://thumbs.modthesims2.com/getimage.php?file=103052

This is whatís called a UV map. When you see talk about polygons, these are them. This map is actually on the simís skin, as itís the shape of the body, not the clothes. Simthiaís UV map only looks like itís on her clothes, but it is an indication of where each part of the clothing mesh goes over her body curves. Each place where the lines intersect is an actual point, some of them project more than others, which is why you may draw a nice straight line on your clothing texture file, and when the sim puts the clothes on, thereís a jagged edge. (Note: a .rar file with the body UV maps for all ages has been added to the attachments at the end of this post.)
http://thumbs.modthesims2.com/getimage.php?file=103053 http://thumbs.modthesims2.com/getimage.php?file=103054

Hereís the reason I mention the importance of the UV map when skinning. The UV map, as I said, has angles. These angles are smoothed out a bit in body shop, and more in the game. A lot of the smoothness you see in-game is an optical illusion created by the shading and highlighting on the texture file, the bump maps, and other in-game lighting. If you become familiar with the UV maps, you can better take advantage of the angles so that your creations are smoothed realistically. Here you can see some lovely straight and perfect lines as they appear on the texture (which is 2D) and how they change when theyíre laid over the three dimensional shape of the sim. http://thumbs.modthesims2.com/getimage.php?file=103055

And while weíre here, Iíd also like to show how the image changes as it goes from Body Shop into the game. What you see in Body Shop is not what you get, unfortunately, so itís always good to check it out in-game. (BTW, this is why we ask that you submit in-game screenshots for your uploads at MTS2) This is also why, if you copy and paste something onto a texture, it can become distorted when itís actually applied to the skin. Imagine taking a bathing suit with a geometric print and stretching it over a basketball, and youíll get the idea. If you lay the texture file for the UV map over the texture for your skin and make it transparent enough only just to see, you can use it as a frame of reference as to where you need to distort your 2D image so it works in 3D. http://thumbs.modthesims2.com/getimage.php?file=103056

Now what we have here is an illustration of the mesh of Simthiaís outfit. The mesh is the actual shape. No changing of alpha or texture files is going to alter this. Imagine the plastic display cover for a doll Ė itís shaped to fit over that doll, so you canít just remove it from one doll and fit it over a different one. And you can paint on it, but youíre still going to see the shape of it on the parts that arenít painted. So the mesh for an outfit for one particular gender and age canít just be copied and pasted to another, and simply blacking out the alpha file is going to cause the simís skintone to jump out and fill in the blanks, leaving flesh-colored bumps. The only place you can change the shape of an outfit by changing the alpha is wherever the mesh is skintight. http://thumbs.modthesims2.com/getimage.php?file=103057

Now, this is the texture file for Simthiaís pants. As you can see, itís an illustration that includes lines, shading, and highlights, which gives it the illusion of being three dimensional. In reality, itís two dimensional and stretchy and flexible, just like swimsuit or t-shirt knit fabrics in real life. It will get laid over the mesh and stretched to fit. This is how a single texture can be used for fit, normal, and fat sims, and why, if you copy and paste something onto, say, a shirt, it sometimes gets distorted when it shows up on the sim. If you open up a texture file for an outfit that has visible side seams, youíre going to find them on only one half of the outfit (to allow for expansion) and also why the color extends beyond the edges a smidge. http://thumbs.modthesims2.com/getimage.php?file=103058

This is the second file that comprises the texture Ė the alpha file. Itís sort of like a mask, with the white parts allowing the texture to show through, and the black parts blocking it out. Some outfits will have grey, which allows a part of the texture to show through. Youíll see this in something like eyeshadow files, because it can also give a fade-out effect. http://thumbs.modthesims2.com/getimage.php?file=103059

Now hereís the interesting phenomenon I mentioned before Ė the skintone jumping out to the mesh. Iíve blurred poor Simthia a bit to protect the sensibilities of delicate users, but you can see how the shading and highlighting that makes the skin itself pops right out to the clothing mesh when the alpha file for the clothes is completely blacked out. If youíve ever tried fiddling with the alpha files and wondered why you got those funny bumps, well, here is exactly what happened to you. http://thumbs.modthesims2.com/getimage.php?file=103060

So you see, your sim is built from the inside out. Over the skeleton is the UV map Ė the polygons that make the sim 3-dimensional. Over those polygons that make your sim is the clothing mesh (or hair mesh or glasses or anything else thatís bigger than the simís body or head), and the texture is just the fabric laid over it. While they work together, each element has its own unique function, so alterations to one may or may not affect the others (and if they do, it might not be what youíre looking for.) http://thumbs.modthesims2.com/getimage.php?file=103061

31st Jul 2005, 12:59 AM
Wow ... that's awesome! You explained it so well!

I'm a complete noob at all of this, and you somehow managed to help me understand what all those thingamawhidgets are ... UVmap, alpha file, etc.

I suddenly don't feel as clueless anymore, lol! :lol:

2nd Aug 2005, 5:42 PM
Nice one...

3rd Aug 2005, 9:31 PM
thanks for sharing. Can't wait for the next tutorial
I'm a beginner in skinning

3rd Aug 2005, 9:49 PM
Thanks for the great Tutorial! I'll put it to good use! Soon, anyway... :)

28th Sep 2005, 4:39 PM
Thank you - I'm gradually getting the idea.

By the way - does anyone know of a way to view modified skins outside of BodyShop or without going through the whole CAF/CAS thing in-game. I'd like to take a peek at how they would look in-game if poss. I read somewhere about SimShow but I think that is for the original Sims, not for "The Sims 2"?

29th Sep 2005, 2:42 AM
Hey Faylen you rock in your tutorials! Thank you very much!

29th Sep 2005, 3:53 PM
I sure wish there were a way to do the in-game view without getting out of body shop. It would certainly make tutorial-writing easier. Even if there were a way to keep the game and BS running at the same time. (I know >why< that can't be done, but I wish it could, anyway.)

11th Oct 2005, 11:05 PM
Thanks for the tutorial, but your images seem to have conked out. I'd really appreciate an update.

4th Nov 2005, 11:51 PM
masterduurk - I also noticed the images are missing. Thankfully, they are still there in the Word Document in the downloadable .rar. file ...

14th Dec 2005, 3:20 PM
All better now. Sorry it took so long - only got on here today.

4th Jan 2006, 2:12 AM
that is soooo cool!!!

4th Jan 2006, 2:17 AM
I realy think what you siad is useful!!!

5th Jan 2006, 7:01 AM
Thanks for the down to basics tutorial. I wsa getting bored withe the game until I started trying to figure out the different ways to create custom content and stretch the limits. I am still very very very new to all of this but your tutorials (all of them) as well as the amazing building tutorials on this site have renewed my interest. I'm sure I'll be saved from bordom now for a millenia!

P.S. thanx again! u rawk!

7th Jan 2006, 12:39 PM
Thanks, i just started and that was a great explaination for a beginer

2nd Feb 2006, 6:20 PM
Thank you for helping me, Faylen, im sorry that i botherd so much in that chat :sorry: , but vharshyde really, really hurt my feelings :sadpanda: . i guess he propably said some things about me after i left. i understand now but im gonna make a long top transparent that overlaps a skirt so it creates the illusion of a dress with more than one layer. thanks again for being the only nice one in that chat. the reason that i wanna make the dress so badly is that my favourate teacher in our school recently got married and i really liked her dress so i wanted to make one just like that and its my last year that im gonna have class with her... ive been with her for seven years...

so thanks
:valentine sweet :puppy: puppy :bunny:

14th Apr 2006, 4:11 AM
wow... that is pretty cool....

22nd Nov 2006, 7:46 PM
Where are all of the pictures? all but a few are "x"ed out.

23rd Nov 2006, 12:32 AM
They were all below the article, but I put them back in place, the thumbs server had changed. So they all work again.

15th Jan 2007, 1:58 PM
Thank you very much for a good explanation. I want to learn about skinning, this will be very useful.

23rd May 2007, 1:33 PM
At long last i'm here also. Time to learn how to create and recreate my favorite costumes for my themed hoods. Thanks so much.

Double B
29th Jun 2007, 12:08 PM
A question. How do you change the meshes?? Is there a tutorial for doing this or something?? Cause it would realy help me out.

16th Jul 2007, 2:20 AM
So THAT'S how that works!

I've been playing Sims 2 for a while now, but I only recently got the guts to try my hand at skinning and meshing.

...I have a lot to learn, lol.

17th Aug 2007, 11:57 PM
uhmnn... i dont know exactly how to say this.. but some of the tops in the adult female everyday clothing thingy are.. misshapen.. they have jagged edges. at first, it was only two or three items, now its a whole bunch... i was wondering if u could help me with that...?

11th Aug 2008, 2:55 AM
Thanks for the tutorial! I've tried my hand at recoloring clothing, to have the skin tone pop out with the mesh, and other times had it come out just how I wanted it. This makes it so much simplier to understand how things work, and what they actually mean. :)

30th Mar 2009, 10:42 PM
Whoa that's wicked.

Cousin Barney
21st Jun 2009, 3:27 AM
Thanks so much! I was looking for UVmaps of skins... I was trying to add a tattoo to a skintone and it came out distorted.