Faylen
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, it’s helpful to understand how all the components of a sim go together. I’ll be focusing on sims, but many of the concepts here apply equally to objects. Let’s start from the beginning. This is a picture of a skeleton in Maya, a 3D animation program. All sims have these skeletons – 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 isn’t going to change – even if you stretch skeleton. Straaaaange things will happen!
http://thumbs.modthesims2.com/getimage.php?file=103051
Here is our model, Simthia. She’s 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 it’s important to know how they work together. http://thumbs.modthesims2.com/getimage.php?file=103052
This is what’s called a UV map. When you see talk about polygons, these are them. This map is actually on the sim’s skin, as it’s the shape of the body, not the clothes. Simthia’s UV map only looks like it’s 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, there’s 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
Here’s 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 they’re laid over the three dimensional shape of the sim. http://thumbs.modthesims2.com/getimage.php?file=103055
And while we’re here, I’d 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 it’s 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 it’s actually applied to the skin. Imagine taking a bathing suit with a geometric print and stretching it over a basketball, and you’ll 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 Simthia’s 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 – it’s shaped to fit over that doll, so you can’t just remove it from one doll and fit it over a different one. And you can paint on it, but you’re still going to see the shape of it on the parts that aren’t painted. So the mesh for an outfit for one particular gender and age can’t just be copied and pasted to another, and simply blacking out the alpha file is going to cause the sim’s 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 Simthia’s pants. As you can see, it’s an illustration that includes lines, shading, and highlights, which gives it the illusion of being three dimensional. In reality, it’s 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, you’re 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 – the alpha file. It’s 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. You’ll 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 here’s the interesting phenomenon I mentioned before – the skintone jumping out to the mesh. I’ve 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 you’ve 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 – 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 that’s bigger than the sim’s 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 you’re looking for.) http://thumbs.modthesims2.com/getimage.php?file=103061
Before you start skinning, it’s helpful to understand how all the components of a sim go together. I’ll be focusing on sims, but many of the concepts here apply equally to objects. Let’s start from the beginning. This is a picture of a skeleton in Maya, a 3D animation program. All sims have these skeletons – 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 isn’t going to change – even if you stretch skeleton. Straaaaange things will happen!
http://thumbs.modthesims2.com/getimage.php?file=103051
Here is our model, Simthia. She’s 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 it’s important to know how they work together. http://thumbs.modthesims2.com/getimage.php?file=103052
This is what’s called a UV map. When you see talk about polygons, these are them. This map is actually on the sim’s skin, as it’s the shape of the body, not the clothes. Simthia’s UV map only looks like it’s 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, there’s 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
Here’s 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 they’re laid over the three dimensional shape of the sim. http://thumbs.modthesims2.com/getimage.php?file=103055
And while we’re here, I’d 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 it’s 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 it’s actually applied to the skin. Imagine taking a bathing suit with a geometric print and stretching it over a basketball, and you’ll 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 Simthia’s 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 – it’s shaped to fit over that doll, so you can’t just remove it from one doll and fit it over a different one. And you can paint on it, but you’re still going to see the shape of it on the parts that aren’t painted. So the mesh for an outfit for one particular gender and age can’t just be copied and pasted to another, and simply blacking out the alpha file is going to cause the sim’s 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 Simthia’s pants. As you can see, it’s an illustration that includes lines, shading, and highlights, which gives it the illusion of being three dimensional. In reality, it’s 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, you’re 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 – the alpha file. It’s 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. You’ll 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 here’s the interesting phenomenon I mentioned before – the skintone jumping out to the mesh. I’ve 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 you’ve 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 – 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 that’s bigger than the sim’s 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 you’re looking for.) http://thumbs.modthesims2.com/getimage.php?file=103061