FieldLines

Field::new(charges, lines_per_charge, bounds) traces the field lines of point charges once (Charge::new(x, y, q)). The lines leave the positive charges, evenly spaced, and end on a negative charge or at bounds. FieldLines draws them on together over draw seconds, each with an arrowhead at its middle. Then, with test_charge: Some(i), a small charge follows line i. field.at(x, y) gives the field and field.lines() the points. Gallery scene: FieldLines.

FieldLines 6 sPlayUnmuteCopy render command

use std::sync::OnceLock;

use fframes_kit::prelude::*;

fn figure<'a>(ui: &mut Ui<'a, '_, '_>) -> Svgr<'a> {
    static FIELD: OnceLock<Field> = OnceLock::new();
    let field = FIELD.get_or_init(|| {
        Field::new(
            vec![Charge::new(-2.5, 0.0, 1.0), Charge::new(2.5, 0.0, -1.0)],
            16,
            (-7.3, -4.1, 7.3, 4.1),
        )
    });
    ui.show(FieldLines {
        field: Some(field),
        delay: 0.5,
        test_charge: Some(2),
        ..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).

FieldLines

Field	Type	Default	Description
field	Option<&Field>	None	The traced field to draw, built once in the video’s constructor; None draws nothing.
delay	f32	0.0	Seconds after the local start before the lines begin to draw.
draw	f32	1.5	Seconds the lines take to draw on, all together.
arrows	bool	true	Draws an arrowhead at the middle of each line.
test_charge	Option<usize>	None	Index of the line the small test charge follows after the lines are drawn; None for no test charge.
speed	f64	1.5	Speed of the test charge along its line in units of ui.space per second.
charge_radius	f32	30.0	Radius of the charge discs in pixels; the test charge is 0.4 times as big.
positive_color	Color	theme.colors.highlight	Colour of positive charges.
negative_color	Color	theme.colors.accent	Colour of negative charges.
line_color	Color	theme.colors.muted	Colour of the field lines and their arrowheads.
test_color	Color	theme.colors.title	Colour of the test charge.
stroke_width	f32	theme.stroke.thin	Width of the field lines in pixels.
enter	Option<EnterAnim>	None	How the charges draw in; None shows them from the start.
exit	Option<ExitAnim>	None	How the charges leave at the end of the container; None stays.
parts_enter	Option<FadeIn>	None	How the lines, signs and the test charge fade in; None for none.
parts_exit	Option<FadeOut>	None	How the lines and the test charge fade out before the end; None for none.

Feature physics · Source