$bodygroup
$bodygroup is a QC command that defines a group of meshes that can be turned on or off, or changed entirely. Server code can change their state.

Example
This body group allows a weapon to have iron sights, laser sights, or no sights at all:
$bodygroup sights
{
studio ironsights
studio laser_dot
blank
}
This body group defines the entire chest region of the model, which spans multiple bones:
$bodygroup chest
{
studio chest_with_no_armor
studio chest_with_light_armor
studio chest_with_heavy_armor
studio chest_with_super_armor
}

Bodygroups in Level of Detail Meshes
Using Level of Detail meshes - especially for high-poly geometry - is highly recommended. Body groups can be used in $lod
strings in the same method as normal geometry meshes:
$lod 12
{
replacemodel chest_with_no_armor chest_with_no_armor_lod1
replacemodel chest_with_light_armor chest_with_light_armor_lod1
replacemodel chest_with_heavy_armor chest_with_heavy_armor_lod1
replacemodel chest_with_super_armor chest_with_super_armor_lod1
}
$lod 18
{
replacemodel chest_with_no_armor chest_with_no_armor_lod2
replacemodel chest_with_light_armor chest_with_light_armor_lod2
replacemodel chest_with_heavy_armor chest_with_heavy_armor_lod2
replacemodel chest_with_super_armor chest_with_super_armor_lod2
}
$shadowlod
{
replacemodel chest_with_no_armor chest_with_no_armor_lod2
replacemodel chest_with_light_armor chest_with_light_armor_lod2
replacemodel chest_with_heavy_armor chest_with_heavy_armor_lod2
replacemodel chest_with_super_armor chest_with_super_armor_lod2
}
Programming
To change a body group's state:
static int BodyGroup_Sights = FindBodygroupByName("sights"); // calculate this value once
SetBodygroup( BodyGroup_Sights , 1 ); // laser dot
By default, CBaseAnimating
supports 4,294,967,296 combinations (32 bits), and CBaseViewModel
supports 256 (8 bits). You can raise either of these by editing the relevant SendProp for m_nBody
.
To calculate how many combinations you need, multiply the size of all your bodygroups together. The examples on this page total 3 * 4 = 12...but add two more groups the same size and you're up at 144. The figure grows exponentially.