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//! The bearing: what [`Direction::With`](crate::Direction) and [`Direction::Against`](crate::Direction) are measured against (§3.12).
use std::time::Duration;
use crate::protocol::opcode::{BEARING_PER_AXIS, BEARING_VECTOR};
/// How the box decides whether physical motion runs with or against its own injection.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default)]
pub enum BearingMode {
/// Each axis compares its own sign against its own bearing, independently (the default).
#[default]
PerAxis,
/// The aim is projected onto the injected XY vector: only the part of the physical delta lying
/// along the injection is weighed, and the part across it passes untouched. Smoother on
/// diagonals; X and Y stop being independent.
///
/// One relative scale governs the whole aim, the lower of X's and Y's, so setting only X's
/// weighs Y's motion too. `RESP(LOCKS)` reports that effective number on both relative entries.
///
/// The projection moves motion between the axes, and each axis's absolute scale then applies to
/// what the projection left rather than to the sign the report carried: an absolute scale is a
/// statement about what reaches the PC, so a block covers motion the projection put there.
Vector,
}
impl BearingMode {
/// The wire `mode` byte.
pub fn as_u8(self) -> u8 {
match self {
BearingMode::PerAxis => BEARING_PER_AXIS,
BearingMode::Vector => BEARING_VECTOR,
}
}
/// Map a wire `mode` byte to a [`BearingMode`], or `None` for an unknown value.
pub fn from_u8(v: u8) -> Option<BearingMode> {
Some(match v {
BEARING_PER_AXIS => BearingMode::PerAxis,
BEARING_VECTOR => BearingMode::Vector,
_ => return None,
})
}
}
/// The configured bearing (`RESP(OPTIONS, BEARING)`, §4.14).
///
/// [`Default`] is what a box holds out of the box, so a [`MockBox`](crate::MockBox) answers what real
/// hardware would: [`BEARING_WINDOW_DEFAULT`](crate::BEARING_WINDOW_DEFAULT) in
/// [`BearingMode::PerAxis`].
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct Bearing {
/// How long the direction of the last injected delta stays the thing
/// [`Direction::With`](crate::Direction) and [`Direction::Against`](crate::Direction) are measured
/// against. `None` = never, so the relative directions are inert whatever their scale. Whole
/// milliseconds on the wire, so this reads back rounded.
pub window: Option<Duration>,
/// Whether the bearing is read per axis or as one vector.
pub mode: BearingMode,
}
impl Default for Bearing {
fn default() -> Bearing {
Bearing {
window: Some(crate::BEARING_WINDOW_DEFAULT),
mode: BearingMode::PerAxis,
}
}
}
impl Bearing {
/// Decode a `RESP(OPTIONS, BEARING)` payload (§4.14): `[what][id][window u16 LE][mode]`.
pub(crate) fn from_payload(p: &[u8]) -> Option<Bearing> {
if p.len() < 5 {
return None;
}
let ms = u16::from_le_bytes([p[2], p[3]]);
Some(Bearing {
window: (ms != 0).then(|| Duration::from_millis(ms as u64)),
mode: BearingMode::from_u8(p[4])?,
})
}
/// Whether a bearing is held at all; the relative directions do nothing when it is not.
pub fn is_live(&self) -> bool {
self.window.is_some()
}
}