Construction and Filenames - The Sims 1 Modding Info
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Skins for The Sims are made up of multiple files:
.SKN: Files containing the mesh data. Many skins use multiple .SKN files.
.BMP: Texture images for the meshes stored in the .SKN files.
.CMX: A file containing a list of .SKN files and how they fit to the Sims skeleton. Head and body skins use their own separate .CMX files.
The most common errors I encounter while skin making ( that isn’t mesh issues ) are mistakes made with the filenames for skins. The Sims is very strict with most filenames, so if you run into a problem with your skin not working: always check the filenames first, and make sure the filename references within the .SKN and CMX files are correct as well ( you can check and fix them by opening the .SKN / .CMX files in a text editor. )
Let’s look at the .SKN files first, I will be using my wasp skin as the example here:
Here is the filename for the body mesh of the wasp skin:
xskin_BX21FAskn_xzywasp-PELVIS-BODY.skn
Now, the segments of the filename made more obvious:
[xskin][_B][X21][FA][skn][_xzywasp][-PELVIS][-BODY][.skn]
Explanations for these segments:
[xskin] : Indicates that this is a skin mesh data file.
[_B] : Indicates that this is data for a body skin. Skin data for heads use “C” to identify them. ( ...C as in “cranium” I guess? ) There are also indicators for alternate outfits: “L” for lingerie / pajamas, “W” for winter, “S” for swimwear, and “F” for formal.
[X21] : The ID for the skin. Must be 3 letters / numbers and not be shared with other skins or will result in conflicts. If a skin unexpectedly uses textures / meshes from another skin, then that means there is an ID conflict,
[FA] : Indicates that this skin data is for the feminine adult bodytype. Masculine adult bodytypes use “MA” to identify them. For child bodytypes, replace the "A" with "C": "FC" and "MC."
[skn] : Indicator for the body shape. This is a skinny body. Larger bodies use “fat,” average bodies use “fit,” and child bodies use “chd.”
[_xzywasp] : The name for the skin.
[-PELVIS] : The base bone of attachment for the skin mesh. If the skin mesh contains vertex data for multiple bones of the skeleton, then use the pelvis bone for the base bone. If the skin mesh does not contain vertex data for any bones, then attach it to whatever bone works best.
[-BODY] : A basic description of what bodypart the mesh is. Example: the wing mesh data for the wasp skin uses “-WINGS.”
[.skn] : The filetype.
Now, here are a few lines from the .SKN file itself:
xskin_BX21FAskn_xzywasp-PELVIS-BODY
BX21FASknmed_xzywasp
19
PELVIS
R_LEG
R_LEG1
R_FOOT
R_TOE0
Now, an explanation:
xskin_BX21FAskn_xzywasp-PELVIS-BODY : Filename of the .SKN file
BX21FASknmed_xzywasp : Texture name
19 : Start of mesh data
PELVIS
R_LEG
R_LEG1
R_FOOT
R_TOE0
The filename must match the name of the .SKN file, and the texture name must match the name of the .BMP file to use for the mesh’s texture. If the .SKN is for a body with multiple skintone options, the name can be any of the texture variants.
Now, we will look at the .BMP file for the wasp body:
BX21FASkndrk_xzywasp.bmp
The segments made obvious:
[B][X21][FA][Skn][drk][_xzywasp][.bmp]
[B] : This texture is for a body mesh.
[X21] : The skin ID.
[FA] : This is for the feminine adult bodytype.
[Skn] : This is a skinny bodyshape.
[drk] : Indicates for this texture to show when the dark skintone option is selected when creating a Sim. Medium skintones use “med” and light skintones use “lgt.”
[_xzywasp] : The skin name.
[.bmp] : The filetype.
And now the .CMX file:
BX21FASkn_xzywasp.cmx
The segments:
[B][X21][FA][Skn][_xzywasp][.cmx]
[B] : This texture is for a body mesh.
[X21] : The skin ID.
[FA] : This is for the feminine adult bodytype.
[Skn] : This is a skinny bodyshape.
[_xzywasp] : The skin name.
[.cmx] : The filetype.
A look at the data inside the .CMX file:
// Character File. Copyright 1997, Maxis Inc.
version 300
0
1
BX21FASkn_xzywasp
0
0
3
PELVIS
xskin_BX21FAskn_xzywasp-PELVIS-BODY
0
0
PELVIS
xskin_BX21FAskn_xzywasp_butt-PELVIS-BUTT
0
0
SPINE2
xskin_BX21FAskn_xzywasp_wings-SPINE2-WINGS
0
0
0
An explanation:
// Character File. Copyright 1997, Maxis Inc. : Copyright info
version 300
0
1
BX21FASkn_xzywasp : Filename of the .CMX file
0
0
3 : Number of attached .SKN files
PELVIS : Base bone
xskin_BX21FAskn_xzywasp-PELVIS-BODY : .SKN attached to base bone
0
0
PELVIS : Base bone
xskin_BX21FAskn_xzywasp_butt-PELVIS-BUTT : .SKN attached to base bone
0
0
SPINE2 : Base bone
xskin_BX21FAskn_xzywasp_wings-SPINE2-WINGS : .SKN attached to base bone
0
0
0
Learning how to create these files was very obnoxious when I first started learning how to create custom skins for The Sims, but once figured out it isn’t too bad. Tools such as CMX Maker and Sims-Skin-Renamer make the process much easier.
I also highly recommend extracting assets from The Sims .FAR files with the FarOut tool and examining them to learn how they work.
Important Note: It is not possible to replace nude skins for Sims, the game will overwrite any attempts to do so when the game starts. This was introduced with Deluxe and Unleashed. So unfortunately your non-human Sims will have to shed their skin whenever they use a shower / bathtub. Someone who contacted me to ask about this shared this [ webpage they found with information on the topic, the info can be found under the “Sets” section. ]
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