# GasBox

> GasMotion::new(GasSetup { .. }) steps count hard balls in a box once, at 240 steps a second: elastic collisions between equal masses and with the walls…

Page: https://fframes-kit.pages.dev/docs/physics/gas-box/
Cargo feature: `physics` (`fframes-kit = { version = "..", features = ["physics"] }`)

`GasMotion::new(GasSetup { .. })` steps `count` hard balls in a box once, at 240 steps a
second: elastic collisions between equal masses and with the walls, with an optional
`Heat { at, to, over }` that brings the temperature to `to` times its start. The start
positions (a grid with jitter) and the directions come from `seed`. The steps use only
`+ - × ÷` and `√`, so the same setup gives the same frames on every run and machine.
`GasBox` draws the particles, slow ones in `slow_color` and those faster than the start's
root mean square speed in `fast_color`, and a thermometer with the factor `T × ..`. Build
the motion in the video's constructor. `particles`, `temperature` and `rms_speed` give the
numbers. Gallery scene: `GasBox`.

Gallery clip of `GasBox`: https://fframes-kit.pages.dev/media/scenes/GasBox-662ff21c.mp4

```rust
use fframes_kit::prelude::*;

struct Lesson {
    gas: GasMotion,
}

impl Lesson {
    fn new() -> Self {
        let setup = GasSetup {
            seed: 7,
            count: 60,
            seconds: 7.0,
            heat: Some(Heat { at: 2.5, to: 3.0, over: 1.5 }),
            ..GasSetup::default()
        };
        Self { gas: GasMotion::new(setup) }
    }

    fn figure<'a>(&'a self, ui: &mut Ui<'a, '_, '_>) -> Svgr<'a> {
        ui.show(GasBox {
            motion: Some(&self.gas),
            scale: 1.4,
            ..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`).

### GasBox

| Field | Type | Default | Description |
| --- | --- | --- | --- |
| `motion` | `Option<&GasMotion>` | `None` | The simulated particles to draw, built once in the video's constructor; `None` draws nothing. |
| `center` | `(f64, f64)` | `(0.0, 0.0)` | The middle of the box, in units of `ui.space`. |
| `scale` | `f64` | `1.0` | Units of `ui.space` per meter. |
| `delay` | `f32` | `0.0` | Seconds after the container's start before the particles start to move. |
| `time_scale` | `f32` | `1.0` | Speed of the motion over local time; 2 runs twice as fast, 1 is real time. |
| `thermometer` | `bool` | `true` | Draws a bar right of the box that fills with the temperature, up to the highest one the motion reaches. |
| `labels` | `bool` | `true` | Writes the temperature factor over the start (`T × 1.5`) above the thermometer. |
| `box_color` | `Color` | `theme.colors.text` | Colour of the box walls and the thermometer frame and label. |
| `slow_color` | `Color` | `theme.colors.accent` | Colour of particles at or below the start's root mean square speed. |
| `fast_color` | `Color` | `theme.colors.highlight` | Colour of faster particles and of the thermometer's level. |
| `stroke_width` | `f32` | `theme.stroke.regular` | Width of the box walls in pixels. |
| `enter` | `Option<EnterAnim>` | `None` | How the box and the thermometer frame draw in; `None` shows them from the start. |
| `exit` | `Option<ExitAnim>` | `None` | How the box and the thermometer frame leave at the end of the container; `None` stays. |
| `parts_enter` | `Option<FadeIn>` | `None` | How the particles and the level fade in; `None` for none. |
| `parts_exit` | `Option<FadeOut>` | `None` | How the particles and the level fade out before the end; `None` for none. |

Feature `physics` · [Source](https://github.com/khanhthanhdev/fframes-kit/blob/main/fframes-kit/src/kits/physics/gas.rs#L218)