$ambientocclusion

Various ambient occlusion maps found in Valve games for eyes and face.

Ambient occlusion is a shading method which helps add realism to local reflection models by taking into account attenuation of light due to occlusion ^[Clarify]. Unlike local methods like Phong shading, ambient occlusion is a global method, meaning the illumination at each point is a function of other geometry in the scene. However, it is a very crude approximation to full global illumination. The soft appearance achieved by ambient occlusion alone is similar to the way an object appears on an overcast day.

Note:Ambient Occlusion maps seem to be used exclusively for eyes and sometimes faces/heads.

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Confirm:Does it actually work?

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Using Ambient Occlusion

Example VMT Syntax

The following example is taken from Left 4 Dead from the model material located in L4D root/materials/models/survivors/teenangst/teenangst_eyeball_l.vmt

EyeRefract
{
$Iris "models/survivors/green_iris2" 
$AmbientOcclTexture "models/survivors/survivor_eye_ao" 
$Envmap "Engine/eye-reflection-cubemap-" 
$CorneaTexture "Engine/eye-cornea" 
$EyeballRadius "0.6" 
$AmbientOcclColor "[.4 .4 .4]" Default 0.33, 0.33, 0.33
$Dilation ".5" 
$ParallaxStrength "0.25" 
$CorneaBumpStrength ".5" 
$halflambert 1
$nodecal 1
$ambientocclusion 1

$RaytraceSphere 1 
$SphereTexkillCombo 0 
}

VMT Parameters

The following is a list of VMT parameters that are needed to enable the Ambient Occlusion:

$AmbientOcclusion "0/1" - Disable/Enable Ambient Occlusion. (1 = enabled, 0 = disabled)

$AmbientOcclColor "[.n .n .n]" - Replacing n with a number of the color (RGB format)

$AmbientOcclTexture "path/to/vtf" - Filename of the ambient occlusion texture to use

Todo: How does $ambientocclusiontexture fit in with all of this?

Source Filmmaker

$AmbientOcclusion "0" can be used to toggle SSAO off on a specific model; for example, a prop in a skybox.

See also

• Phong materials
• $phong
• $basetexture
• $envmapmask (specular mask)
• $envmap (environment map)
• $selfillum