Houdini 20.5 Nodes VOP nodes

Karma Light Filter Attenuation VOP node

Karma Light Filter that controls how the light intensity/color changes over distance.

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Since 19.5

Overview

You can assign a light filter prim to a light to modify the light rays it sends. See Karma light filters for more information.

This filter changes the attenuation of the light, this is, how the intensity/color of the light changes over distance from the light source.

Sometimes a physically unrealistic falloff seems more “natural” or can be easier to light with in a scene. You can also tint light as it falls off to create artistic effects, such as making a light more blue farther away.

Parameters

Style

The type of attenuation.

Physically Correct

This is the normal behaviour for lights in karma. The intensity of the light falls off with the distance squared.

Half Distance

You specify a distance at which the light attains half the intensity that it is at the origin of the light. This is modeled mathematically as

Cl = H / (H + D)

where H is the half distance and D is the distance from the light source. When D is 0, we end up with H/H which is 1. When D is equal to H (the half-distance) the intensity is H/(H+H), which is half the intensity.

The light is never fully extinguished no matter the distance from the source.

Quadratic Polynomial

The falloff of intensity is controlled by a quadratic polynomial. This is modeled mathematically as

Cl = 1 / (a + b*D + c*D*D)

Where the coefficients of the polynomial are: a (Constant), b (Linear) and c` (Quadratic), and D is the distance from the light source.

When a == 0, b == 0 and c == 1, this is equivalent to physically correct attenuation.

Ramp

The falloff of the light is controlled by the ramp. The lookup into the ramp is controlled linearly and clamped between the Ramp Near and Ramp Far values.

Distance

When Style is Half Distance, this is the distance at which the intensity of the light source is half it’s value at the origin.

Constant

When Style is Quadratic Polynomial, this is the constant term.

Linear

IWhen Style is Quadratic Polynomial, this is the linear term.

Quadratic

When Style is Quadratic Polynomial, this is the quadratic term.

Ramp Near

When Style is Ramp, this is distance which corresponds to the start of the ramp. Distances closer than this will use the first value in the ramp.

Ramp Far

When Style is Ramp, this is distance which corresponds to the end of the ramp. Distances farther than this will use the last value in the ramp.

Ramp

When Style is Ramp, and the distance is between Ramp Near and Ramp Far, the filter multiplies the light by the value in this ramp. You can vary the color lightness to scale the light intensity, or vary the color to tint the light at different distances (for example, making the light more blue the more distant it is).

See also

VOP nodes