Doppler

Cargo featurefeatures = ["physics"]

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A source moving right from start at source_speed m/s sends out a front every period seconds, and the fronts spread at wave_speed m/s. They bunch up ahead of the source and spread out behind it. At or above the wave speed they pile into a cone. A front fades as it grows and is gone at max_radius meters. Listeners ahead and behind (meters from start) show the frequency they hear, f c / (c ∓ v), once the first front has reached them. The source’s own frequency sits above it, on a chip of the background. heard and fronts give the numbers. Gallery scene: Doppler.

Doppler demo, first frame — `Doppler` 5.5 s

use fframes_kit::prelude::*;

fn figure<'a>(ui: &mut Ui<'a, '_, '_>) -> Svgr<'a> {
    ui.show(Doppler {
        start: (-3.5, 0.0),
        scale: 0.7,
        source_speed: 1.0,
        wave_speed: 3.0,
        period: 0.4,
        ahead: Some(8.0),
        behind: Some(-4.0),
        ..ui.defaults()
    })
}

API

Components are plain structs. Set the fields you need and fill the rest with ..ui.defaults(): the defaults below come from the current theme (theme. values are fields of Theme).

Doppler

Field	Type	Default	Description
`start`	`(f64, f64)`	`(-4.0, 0.0)`	Where the source starts, in units of `ui.space`; meters below are measured from it.
`scale`	`f64`	`1.0`	Units of `ui.space` per meter.
`source_speed`	`f64`	`1.0`	Speed of the source to the right in m/s; at or above `wave_speed` the fronts pile into a cone.
`wave_speed`	`f64`	`3.0`	Speed the wavefronts spread at in m/s.
`period`	`f64`	`0.4`	Seconds between two wavefronts; the source’s own frequency is its inverse.
`max_radius`	`f64`	`6.0`	Radius in meters where a front is gone; it fades out on the way.
`ahead`	`Option<f64>`	`Some(10.0)`	Listener in meters from `start`, to the right of the source; `None` for none.
`behind`	`Option<f64>`	`Some(-2.5)`	Listener in meters from `start`, to the left of the source; `None` for none.
`labels`	`bool`	`true`	Writes the source’s frequency above it and the frequency each listener hears once the first front reaches it.
`delay`	`f32`	`0.0`	Seconds after the container’s start before the source starts moving.
`time_scale`	`f32`	`1.0`	Speed of the motion over local time; 2 runs twice as fast, 1 is real time.
`source_color`	`Color`	`theme.colors.accent`	Colour of the source and its frequency label.
`wave_color`	`Color`	`theme.colors.text`	Colour of the wavefronts.
`listener_color`	`Color`	`theme.colors.highlight`	Colour of the listener marks.
`stroke_width`	`f32`	`theme.stroke.thin`	Width of the wavefronts in pixels.
`enter`	`Option<EnterAnim>`	`None`	How the listener marks draw in; `None` shows them from the start.
`exit`	`Option<ExitAnim>`	`None`	How the listener marks leave at the end of the container; `None` stays.
`parts_enter`	`Option<FadeIn>`	`None`	How the source and the fronts fade in; `None` for none.
`parts_exit`	`Option<FadeOut>`	`None`	How the source and the fronts fade out before the end; `None` for none.

Methods:

fn source(&self, t: f64) -> f64: Meters from start, the source after t seconds.
fn heard(&self, x: f64, t: f64) -> Option<f64>: The frequency in Hz a listener at x meters from start hears while the source is where it is after t seconds: f c / (c - v) ahead of it, f c / (c + v) behind. None ahead of a source at or above the wave speed, where no front has come.
fn fronts(&self, t: f64) -> Vec<(f64, f64)>: The emission time and the radius in meters of every front alive after t seconds, oldest first.

Feature physics · Source