Enum Falloff 

pub enum Falloff {
    Linear,
    Exponential {
        scale: f32,
    },
    Tent {
        center: f32,
        width: f32,
    },
    Curve(Arc<dyn Curve<f32> + Sync + Send>),
}

Describes how the media in a ScatteringTerm is distributed.

This is closely related to the optical density values ScatteringTerm::absorption and ScatteringTerm::scattering. Most media aren’t the same density everywhere; near the edge of space Earth’s atmosphere is much less dense, and it absorbs and scatters less light.

Falloff determines how the density of a medium changes as a function of an abstract “falloff parameter” p. p = 1 denotes where the medium is the densest, i.e. at the surface of the Earth, p = 0 denotes where the medium fades away completely, i.e. at the edge of space, and values between scale linearly with distance, so p = 0.5 would be halfway between the surface and the edge of space.

When processing a ScatteringMedium, the absorption and scattering values for each ScatteringTerm are multiplied by the value of the falloff function, f(p).

Variants

Linear

A simple linear falloff function, which essentially passes the falloff parameter through unchanged.

f(1) = 1 f(0) = 0 f(p) = p

Exponential

An exponential falloff function parametrized by a proportional scale. When paired with an absolute “falloff distance” like the distance from Earth’s surface to the edge of space, this is analogous to the “height scale” value common in atmospheric scattering literature, though it will diverge from this for large or negative scale values.

f(1) = 1 f(0) = 0 f(p) = (e^((1-p)/s) - e^(1/s))/(e - e^(1/s))

Fields

scale: f32

The “scale” of the exponential falloff. Values closer to zero will produce steeper falloff, and values farther from zero will produce gentler falloff, approaching linear falloff as scale goes to +-∞.

Negative values change the concavity of the falloff function: rather than an initial narrow region of steep falloff followed by a wide region of gentle falloff, there will be an initial wide region of gentle falloff followed by a narrow region of steep falloff.

domain: (-∞, ∞)

NOTE, this function is not defined when scale == 0. In that case, it will fall back to linear falloff.

Tent

A tent-shaped falloff function, which produces a triangular peak at the center and linearly falls off to either side.

f(center) = 1 f(center +- width / 2) = 0

Fields

center: f32

The center of the tent function peak

domain: [0, 1]

width: f32

The total width of the tent function peak

domain: [0, 1]

Curve(Arc<dyn Curve<f32> + Sync + Send>)

A falloff function defined by a custom curve.

domain: [0, 1], range: [0, 1],

Implementations

impl Falloff

pub fn from_curve(curve: impl Curve<f32> + Send + Sync + 'static) -> Falloff

Returns a falloff function corresponding to a custom curve.

Trait Implementations

impl Clone for Falloff

fn clone(&self) -> Falloff

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Default for Falloff

fn default() -> Falloff

Returns the “default value” for a type.