orbit-camera 0.1.0

#![deny(missing_docs)]
//! A third-person orbit camera.
//!
//! The camera orbits a focus point that smoothly follows a target. Yaw and
//! pitch are controlled directly; the orbit distance scales with pitch (looking
//! down pulls the camera in, looking up pushes it out) and can be zoomed. The
//! focus point and distance interpolate frame-rate independently. An optional
//! clipping pass pulls the camera in when geometry blocks the line of sight to
//! the focus.
//!
//! The camera produces geometry (eye, focus, up) and projection parameters; it
//! does not depend on any matrix type. Build the view-projection matrix with
//! whatever math library the renderer uses.
//!
//! ```
//! use ga3::Vector;
//! use orbit_camera::OrbitCamera;
//!
//! let mut camera = OrbitCamera::new(Vector::new(0.0, 0.0, 0.0));
//! camera.rotate([0.02, 0.0]);
//! camera.follow(Vector::new(1.0, 0.0, 0.0), 1.0 / 60.0);
//! let view = camera.view();
//! let _eye = view.eye;
//! ```

use collide_ray::Ray;
use ga3::Vector;

/// A source of geometry the camera can clip against.
///
/// Implemented for any collision world that can cast a ray and return the
/// distance to the nearest hit within `max_distance`. With the `collide-mesh`
/// feature this is implemented for [`collide_mesh::CollisionWorld`].
pub trait Clip {
    /// Casts `ray` and returns the distance to the nearest hit no farther than
    /// `max_distance`, or `None` if nothing is hit.
    fn raycast(&self, ray: &Ray<Vector<f32>>, max_distance: f32) -> Option<f32>;
}

#[cfg(feature = "collide-mesh")]
impl Clip for collide_mesh::CollisionWorld {
    fn raycast(&self, ray: &Ray<Vector<f32>>, max_distance: f32) -> Option<f32> {
        collide_mesh::CollisionWorld::raycast(self, ray, max_distance)
    }
}

/// Tunable parameters of an [`OrbitCamera`].
///
/// [`CameraConfig::default`] matches a Zelda-style action-adventure camera. Each
/// field can be overridden for a different feel.
#[derive(Copy, Clone, Debug, PartialEq)]
pub struct CameraConfig {
    /// Lowest pitch in radians (looking up the most). Negative looks up.
    pub min_pitch: f32,
    /// Highest pitch in radians (looking down the most).
    pub max_pitch: f32,
    /// Orbit distance at `min_pitch`.
    pub low_distance: f32,
    /// Orbit distance at `max_pitch`.
    pub high_distance: f32,
    /// Distance the camera never clips below.
    pub min_distance: f32,
    /// Smallest zoom multiplier.
    pub min_zoom: f32,
    /// Largest zoom multiplier.
    pub max_zoom: f32,
    /// Multiplicative zoom step applied per unit of [`OrbitCamera::zoom`] input.
    pub zoom_step: f32,
    /// Height of the focus point above the followed target.
    pub focus_height: f32,
    /// Smoothing strength of the focus point. Larger follows faster.
    pub focus_strength: f32,
    /// Smoothing strength of the orbit distance. Larger reaches the goal faster.
    pub distance_strength: f32,
    /// Distance below which clipping is skipped.
    pub clip_start: f32,
    /// Gap kept between the camera and clipped geometry.
    pub clip_margin: f32,
    /// Initial pitch of a freshly created camera.
    pub default_pitch: f32,
    /// Vertical field of view in radians.
    pub field_of_view: f32,
    /// Near clip plane.
    pub near_plane: f32,
    /// Far clip plane.
    pub far_plane: f32,
}

impl Default for CameraConfig {
    fn default() -> Self {
        Self {
            min_pitch: -0.524,
            max_pitch: 1.047,
            low_distance: 4.0,
            high_distance: 9.0,
            min_distance: 1.0,
            min_zoom: 0.5,
            max_zoom: 2.0,
            zoom_step: 0.2,
            focus_height: 1.5,
            focus_strength: 4.0,
            distance_strength: 8.0,
            clip_start: 0.5,
            clip_margin: 0.2,
            default_pitch: 0.4,
            field_of_view: std::f32::consts::FRAC_PI_3,
            near_plane: 0.1,
            far_plane: 200.0,
        }
    }
}

/// The horizontal movement basis derived from the camera yaw.
///
/// Both vectors lie in the ground plane, so movement input stays level
/// regardless of pitch.
#[derive(Copy, Clone, Debug)]
pub struct MovementBasis {
    /// Direction the camera faces, projected onto the ground plane.
    pub forward: Vector<f32>,
    /// Direction to the camera's right, projected onto the ground plane.
    pub right: Vector<f32>,
}

/// Everything needed to build a view-projection matrix.
#[derive(Copy, Clone, Debug)]
pub struct ViewParameters {
    /// Camera position.
    pub eye: Vector<f32>,
    /// Point the camera looks at.
    pub focus: Vector<f32>,
    /// Up direction (world +Y).
    pub up: Vector<f32>,
    /// Vertical field of view in radians.
    pub field_of_view: f32,
    /// Near clip plane.
    pub near_plane: f32,
    /// Far clip plane.
    pub far_plane: f32,
}

/// A third-person camera that orbits a smoothly following focus point.
#[derive(Copy, Clone, Debug)]
pub struct OrbitCamera {
    yaw: f32,
    pitch: f32,
    zoom_factor: f32,
    distance: f32,
    focus: Vector<f32>,
    config: CameraConfig,
}

impl OrbitCamera {
    /// Creates a camera looking at `target` from the default yaw.
    pub fn new(target: Vector<f32>) -> Self {
        Self::facing(target, 0.0, CameraConfig::default())
    }

    /// Creates a camera looking at `target` from `yaw`, with `config`.
    pub fn facing(target: Vector<f32>, yaw: f32, config: CameraConfig) -> Self {
        let mut camera = Self {
            yaw,
            pitch: config.default_pitch,
            zoom_factor: 1.0,
            distance: 0.0,
            focus: target + Vector::y(config.focus_height),
            config,
        };
        camera.distance = camera.goal_distance();
        camera
    }

    /// Returns the configuration.
    pub fn config(&self) -> &CameraConfig {
        &self.config
    }

    /// Replaces the configuration. The next [`follow`](Self::follow) eases the
    /// camera toward the new distance.
    pub fn set_config(&mut self, config: CameraConfig) {
        self.config = config;
    }

    /// Rotates the camera by `[yaw, pitch]` deltas in radians. Pitch is clamped
    /// to the configured range.
    pub fn rotate(&mut self, delta: [f32; 2]) {
        let [delta_yaw, delta_pitch] = delta;
        self.yaw -= delta_yaw;
        self.pitch = (self.pitch - delta_pitch).clamp(self.config.min_pitch, self.config.max_pitch);
    }

    /// Current yaw in radians.
    pub fn yaw(&self) -> f32 {
        self.yaw
    }

    /// Sets the yaw directly in radians. Use this when the consumer drives the
    /// orientation absolutely (spherical coordinates, snap-to-step yaw) instead
    /// of through [`rotate`](Self::rotate) deltas.
    pub fn set_yaw(&mut self, yaw: f32) {
        self.yaw = yaw;
    }

    /// Current pitch in radians.
    pub fn pitch(&self) -> f32 {
        self.pitch
    }

    /// Sets the pitch directly in radians, clamped to the configured range.
    pub fn set_pitch(&mut self, pitch: f32) {
        self.pitch = pitch.clamp(self.config.min_pitch, self.config.max_pitch);
    }

    /// Current focus point.
    pub fn focus(&self) -> Vector<f32> {
        self.focus
    }

    /// Sets the focus point directly, bypassing the easing in
    /// [`follow`](Self::follow). Use this when the consumer drives the look-at
    /// target itself (cutscenes, custom focus logic).
    pub fn set_focus(&mut self, focus: Vector<f32>) {
        self.focus = focus;
    }

    /// Current orbit distance from the focus point to the eye.
    pub fn distance(&self) -> f32 {
        self.distance
    }

    /// Sets the orbit distance directly, bypassing the easing in
    /// [`follow`](Self::follow). Use this to drive the distance from a custom
    /// model (absolute zoom, aim modes) or a custom clip pass.
    pub fn set_distance(&mut self, distance: f32) {
        self.distance = distance;
    }

    /// Zooms by `amount`. Positive zooms in. Clamped to the configured range.
    pub fn zoom(&mut self, amount: f32) {
        self.zoom_factor = (self.zoom_factor * (-amount * self.config.zoom_step).exp2())
            .clamp(self.config.min_zoom, self.config.max_zoom);
    }

    /// Eases the focus point toward `target` and the orbit distance toward its
    /// pitch-derived goal, frame-rate independently over `timestep` seconds.
    pub fn follow(&mut self, target: Vector<f32>, timestep: f32) {
        let goal_focus = target + Vector::y(self.config.focus_height);
        self.focus +=
            (goal_focus - self.focus) * timed_friction(self.config.focus_strength, timestep);

        let goal_distance = self.goal_distance();
        self.distance += (goal_distance - self.distance)
            * timed_friction(self.config.distance_strength, timestep);
    }

    /// Pulls the camera in if `world` blocks the line of sight from the focus
    /// point to the eye.
    pub fn clip<C: Clip>(&mut self, world: &C) {
        if self.distance <= self.config.clip_start {
            return;
        }
        let direction = (self.eye() - self.focus) / self.distance;
        let ray = Ray::new(self.focus + direction * self.config.clip_start, direction);
        if let Some(hit) = world.raycast(&ray, self.distance - self.config.clip_start) {
            let clipped = (self.config.clip_start + hit - self.config.clip_margin)
                .max(self.config.min_distance);
            if clipped < self.distance {
                self.distance = clipped;
            }
        }
    }

    /// Current eye position.
    pub fn eye(&self) -> Vector<f32> {
        self.eye_at(self.distance)
    }

    /// Eye position the camera would have at an arbitrary orbit `distance`,
    /// using the current yaw, pitch and focus. Useful for custom clip passes
    /// that probe a candidate distance before committing it via
    /// [`set_distance`](Self::set_distance).
    pub fn eye_at(&self, distance: f32) -> Vector<f32> {
        let (sin_pitch, cos_pitch) = self.pitch.sin_cos();
        let (sin_yaw, cos_yaw) = self.yaw.sin_cos();
        self.focus + Vector::new(cos_pitch * sin_yaw, sin_pitch, cos_pitch * cos_yaw) * distance
    }

    /// Eases the yaw toward `look_direction` (projected onto the ground plane),
    /// frame-rate independently. Useful for lock-on steering. `strength`
    /// controls how fast.
    pub fn steer_toward(&mut self, look_direction: Vector<f32>, strength: f32, timestep: f32) {
        use std::f32::consts::{PI, TAU};
        let length = look_direction.x.hypot(look_direction.z);
        if length < 1e-4 {
            return;
        }
        let target_yaw = (-look_direction.x).atan2(-look_direction.z);
        let difference = (target_yaw - self.yaw + PI).rem_euclid(TAU) - PI;
        self.yaw += difference * timed_friction(strength, timestep);
    }

    /// Forward direction projected onto the ground plane.
    pub fn forward_xz(&self) -> Vector<f32> {
        Vector::new(-self.yaw.sin(), 0.0, -self.yaw.cos())
    }

    /// Right direction projected onto the ground plane.
    pub fn right_xz(&self) -> Vector<f32> {
        Vector::new(self.yaw.cos(), 0.0, -self.yaw.sin())
    }

    /// The horizontal movement basis for character input.
    pub fn basis(&self) -> MovementBasis {
        MovementBasis {
            forward: self.forward_xz(),
            right: self.right_xz(),
        }
    }

    /// The parameters needed to build a view-projection matrix.
    pub fn view(&self) -> ViewParameters {
        ViewParameters {
            eye: self.eye(),
            focus: self.focus,
            up: Vector::y(1.0),
            field_of_view: self.config.field_of_view,
            near_plane: self.config.near_plane,
            far_plane: self.config.far_plane,
        }
    }

    fn goal_distance(&self) -> f32 {
        let pitch_ratio =
            (self.pitch - self.config.min_pitch) / (self.config.max_pitch - self.config.min_pitch);
        (self.config.low_distance
            + (self.config.high_distance - self.config.low_distance) * pitch_ratio)
            * self.zoom_factor
    }
}

fn timed_friction(strength: f32, timestep: f32) -> f32 {
    1.0 - (-strength * timestep).exp2()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn eye_sits_above_and_behind_focus() {
        let camera = OrbitCamera::new(Vector::new(0.0, 0.0, 0.0));
        let offset = camera.eye() - camera.focus();
        let length = (offset.x * offset.x + offset.y * offset.y + offset.z * offset.z).sqrt();
        assert!(length > 0.0);
        assert!(offset.y > 0.0);
    }

    #[test]
    fn rotate_clamps_pitch() {
        let mut camera = OrbitCamera::new(Vector::new(0.0, 0.0, 0.0));
        camera.rotate([0.0, 100.0]);
        assert!((camera.pitch() - camera.config().min_pitch).abs() < 1e-5);
        camera.rotate([0.0, -100.0]);
        assert!((camera.pitch() - camera.config().max_pitch).abs() < 1e-5);
    }

    #[test]
    fn follow_moves_focus_toward_target() {
        let mut camera = OrbitCamera::new(Vector::new(0.0, 0.0, 0.0));
        let start = camera.focus();
        camera.follow(Vector::new(10.0, 0.0, 0.0), 1.0 / 60.0);
        assert!(camera.focus().x > start.x);
        assert!(camera.focus().x < 10.0);
    }

    #[test]
    fn set_focus_and_distance_bypass_easing() {
        let mut camera = OrbitCamera::new(Vector::new(0.0, 0.0, 0.0));
        let focus = Vector::new(3.0, 1.0, -2.0);
        camera.set_focus(focus);
        camera.set_distance(5.0);
        assert_eq!(camera.focus(), focus);
        assert_eq!(camera.distance(), 5.0);
    }

    #[test]
    fn set_yaw_is_absolute_and_set_pitch_clamps() {
        let mut camera = OrbitCamera::new(Vector::new(0.0, 0.0, 0.0));
        camera.set_yaw(1.25);
        assert_eq!(camera.yaw(), 1.25);
        camera.set_pitch(100.0);
        assert!((camera.pitch() - camera.config().max_pitch).abs() < 1e-6);
    }

    #[test]
    fn eye_at_matches_eye_for_current_distance() {
        let camera = OrbitCamera::new(Vector::new(1.0, 2.0, 3.0));
        let eye = camera.eye();
        let probed = camera.eye_at(camera.distance());
        assert!((eye - probed).x.abs() < 1e-6);
        assert!((eye - probed).y.abs() < 1e-6);
        assert!((eye - probed).z.abs() < 1e-6);
    }
}