trackball/
first.rs

1use nalgebra::{Point2, RealField, Unit, Vector2, Vector3, convert};
2use simba::scalar::SubsetOf;
3
4/// First person view induced by displacement on screen.
5///
6/// Implements [`Default`] and can be created with `First::default()`.
7///
8/// All methods except [`Self::enabled()`] must be invoked on matching events fired by your 3D
9/// graphics library of choice.
10#[derive(Debug, Clone, Default)]
11pub struct First<N: Copy + RealField> {
12	/// Caches captured yaw axis.
13	ray: Option<Unit<Vector3<N>>>,
14}
15
16impl<N: Copy + RealField> First<N> {
17	/// Captures current yaw axis when entering first person view.
18	pub const fn capture(&mut self, yaw_axis: Unit<Vector3<N>>) {
19		self.ray = Some(yaw_axis);
20	}
21	/// Computes pitch and yaw from cursor/finger displacement vector in screen space.
22	///
23	/// Carries cursor/finger displacements to arcs of the same length on great circles of an
24	/// eye-centered trackball with radius of maximum of half the screen's width and height in
25	/// compliance with [`crate::Orbit`] except that its trackball is target-centered.
26	pub fn compute(&self, vec: &Vector2<N>, max: &Point2<N>) -> Option<(N, N, &Unit<Vector3<N>>)> {
27		self.ray.as_ref().map(|ray| {
28			let max = max.x.max(max.y) * convert(0.5);
29			(vec.y / max, vec.x / max, ray)
30		})
31	}
32	/// Discards captured yaw axis when leaving first person view.
33	pub const fn discard(&mut self) {
34		self.ray = None;
35	}
36	/// Whether a yaw axis has been captured.
37	#[must_use]
38	pub const fn enabled(&self) -> bool {
39		self.ray.is_some()
40	}
41	/// Captured yaw axis.
42	#[must_use]
43	pub const fn yaw_axis(&self) -> Option<&Unit<Vector3<N>>> {
44		self.ray.as_ref()
45	}
46	/// Casts components to another type, e.g., between [`f32`] and [`f64`].
47	#[must_use]
48	pub fn cast<M: Copy + RealField>(self) -> First<M>
49	where
50		N: SubsetOf<M>,
51	{
52		First {
53			ray: self.ray.map(Unit::<Vector3<N>>::cast),
54		}
55	}
56}
trackball/first.rs

trackball/
first.rs
