OneCAD-Draft/src/scene/view/camera.rs

// Arcball orbit camera — quaternion-based rotation, no gimbal lock.
//
// The camera orbits around a `target` point using a unit quaternion (`rotation`)
// that maps the canonical "camera looks down -Z" pose to the current view.
//
// Pan:       translates `target` in the view-plane (no rotation change).
// Orbit:     updates `rotation` via arcball delta — converts screen drag delta
//            to a rotation axis/angle, then pre-multiplies the current quaternion.
// Zoom:      adjusts `distance` (exponential feel).
// Snap:      directly assigns yaw+pitch encoded as a quaternion (for ViewCube).
//
// Coordinate convention: Z-up world space (same as the rest of OpenCADStudio).

use glam::{vec3, DVec3, Mat4, Quat, Vec3};
use iced::{Point, Rectangle};

#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub enum Projection {
    Orthographic,
    Perspective,
}

#[derive(Clone)]
pub struct Camera {
    /// World-space pivot point the camera orbits around. Kept in f64 so a far
    /// pan (large offset-relative coordinate) doesn't lose precision in the
    /// pivot itself — the eventual relative-to-eye render path needs an exact
    /// eye, which derives from this target.
    pub target: DVec3,
    /// Arcball rotation: maps canonical pose to current orientation.
    pub rotation: Quat,
    /// Distance from eye to target.
    pub distance: f32,
    /// Vertical field of view in radians (perspective only).
    pub fov_y: f32,
    pub projection: Projection,

    // --- Legacy yaw/pitch exposed only for ViewCube hit-test compatibility ---
    // Kept in sync with `rotation` whenever orbit() or snap_angles() is called.
    pub yaw: f32,
    pub pitch: f32,
}

impl Default for Camera {
    fn default() -> Self {
        // Default: look straight down at the XY drawing plane (top view, Z-up).
        // yaw = 0, pitch = PI/2  →  eye is directly above target.
        let yaw = 0.0_f32;
        let pitch = std::f32::consts::FRAC_PI_2;
        Self {
            target: DVec3::ZERO,
            rotation: yaw_pitch_to_quat(yaw, pitch, 0.0),
            distance: 60.36,
            fov_y: 45.0_f32.to_radians(),
            projection: Projection::Orthographic,
            yaw,
            pitch,
        }
    }
}

pub const OPENGL_TO_WGPU: Mat4 = glam::mat4(
    glam::vec4(1.0, 0.0, 0.0, 0.0),
    glam::vec4(0.0, 1.0, 0.0, 0.0),
    glam::vec4(0.0, 0.0, 0.5, 0.0),
    glam::vec4(0.0, 0.0, 0.5, 1.0),
);

impl Camera {
    // ── Eye position ───────────────────────────────────────────────────────

    pub fn eye(&self) -> Vec3 {
        // The canonical eye direction is +Z (looking at origin from above).
        // The rotation maps that canonical pose to the current orientation.
        let eye_dir = self.rotation * Vec3::Z;
        self.target.as_vec3() + eye_dir * self.distance
    }

    /// Eye position in full f64 precision (offset-relative world space). Used
    /// by the relative-to-eye render path; the f32 [`eye`] stays for ray/pick
    /// math that operates at human scale.
    #[allow(dead_code)] // consumed by the relative-to-eye uniform (next phase)
    pub fn eye_f64(&self) -> DVec3 {
        let eye_dir = (self.rotation * Vec3::Z).as_dvec3();
        self.target + eye_dir * self.distance as f64
    }

    /// Half-height of the orthographic frustum in world units.
    pub fn ortho_size(&self) -> f32 {
        self.distance * (self.fov_y * 0.5).tan()
    }

    // ── Projection matrices ────────────────────────────────────────────────

    pub fn view_proj(&self, bounds: Rectangle) -> Mat4 {
        let near = self.distance * 0.001;
        let far = self.distance * 1000.0;
        let aspect = bounds.width / bounds.height;

        // Up vector: use the rotation to find which world direction is "up"
        // in the current camera frame.
        let up_dir = self.rotation * Vec3::Y;

        let view = Mat4::look_at_rh(self.eye(), self.target.as_vec3(), up_dir);
        let proj = match self.projection {
            Projection::Perspective => Mat4::perspective_rh(self.fov_y, aspect, near, far),
            Projection::Orthographic => {
                let h = self.ortho_size();
                let w = h * aspect;
                Mat4::orthographic_rh(-w, w, -h, h, near, far)
            }
        };
        OPENGL_TO_WGPU * proj * view
    }

    /// Relative-to-eye view-projection: identical projection, but the view
    /// matrix carries rotation only (translation zeroed). Positions fed to it
    /// must already be expressed relative to the eye (done per-vertex with
    /// double-single precision in the shader), so the large eye translation
    /// never enters the f32 matrix and large-coordinate jitter disappears.
    pub fn view_proj_rte(&self, bounds: Rectangle) -> Mat4 {
        let near = self.distance * 0.001;
        let far = self.distance * 1000.0;
        let aspect = bounds.width / bounds.height;
        let up_dir = self.rotation * Vec3::Y;

        let mut view = Mat4::look_at_rh(self.eye(), self.target.as_vec3(), up_dir);
        // Zero the translation column → pure rotation (world→view basis).
        view.w_axis = glam::vec4(0.0, 0.0, 0.0, 1.0);

        let proj = match self.projection {
            Projection::Perspective => Mat4::perspective_rh(self.fov_y, aspect, near, far),
            Projection::Orthographic => {
                let h = self.ortho_size();
                let w = h * aspect;
                Mat4::orthographic_rh(-w, w, -h, h, near, far)
            }
        };
        OPENGL_TO_WGPU * proj * view
    }

    /// Project a world point to screen pixels with full f64 precision: the
    /// point is made eye-relative in f64 (small numbers near the view) before
    /// the rotation-only projection, so it stays exact at large absolute
    /// coordinates — the CPU equivalent of the GPU's relative-to-eye path.
    /// Returns `None` for points at/behind the eye plane (w ≈ 0).
    #[allow(dead_code)] // consumed by the world_offset-removal CPU migration
    pub fn project_f64(&self, p: glam::DVec3, bounds: Rectangle) -> Option<glam::Vec2> {
        let rel = (p - self.eye_f64()).as_vec3();
        let clip = self.view_proj_rte(bounds) * rel.extend(1.0);
        if clip.w.abs() < 1e-9 {
            return None;
        }
        let ndc = clip.truncate() / clip.w;
        Some(glam::vec2(
            (ndc.x * 0.5 + 0.5) * bounds.width,
            (0.5 - ndc.y * 0.5) * bounds.height,
        ))
    }

    /// Unproject a screen point onto an arbitrary world plane in f64. The ray
    /// is built in eye-relative space (precise), intersected with the plane
    /// expressed relative to the eye, then shifted back by the f64 eye — so the
    /// returned world point keeps full precision at large absolute coordinates.
    #[allow(dead_code)] // consumed by the world_offset-removal CPU migration
    pub fn unproject_on_plane_f64(
        &self,
        screen: Point,
        bounds: Rectangle,
        plane_normal: Vec3,
        plane_point: glam::DVec3,
    ) -> glam::DVec3 {
        let eye = self.eye_f64();
        let ndc_x = (screen.x / bounds.width) * 2.0 - 1.0;
        let ndc_y = 1.0 - (screen.y / bounds.height) * 2.0;
        let inv = self.view_proj_rte(bounds).inverse();
        // Ray origin / direction in eye-relative space.
        let (ray_origin, ray_dir) = match self.projection {
            Projection::Perspective => {
                let near_pt = inv.project_point3(Vec3::new(ndc_x, ndc_y, 0.0));
                let far_pt = inv.project_point3(Vec3::new(ndc_x, ndc_y, 1.0));
                (near_pt, (far_pt - near_pt).normalize())
            }
            Projection::Orthographic => {
                let origin = inv.project_point3(Vec3::new(ndc_x, ndc_y, 0.0));
                let forward = self.rotation * Vec3::NEG_Z;
                (origin, forward)
            }
        };
        // Plane point relative to the eye (small) for a precise intersection.
        let plane_rel = (plane_point - eye).as_vec3();
        let denom = ray_dir.dot(plane_normal);
        let rel_hit = if denom.abs() < 1e-6 {
            plane_rel
        } else {
            let t = (plane_rel - ray_origin).dot(plane_normal) / denom;
            ray_origin + ray_dir * t
        };
        eye + rel_hit.as_dvec3()
    }

    /// Eye position split into two f32 (high + low) emulating f64, for the
    /// double-single relative-to-eye shaders. `high + low ≈ eye` to ~f64
    /// precision; the shader subtracts these from each vertex's own high/low.
    pub fn eye_high_low(&self) -> ([f32; 3], [f32; 3]) {
        let e = self.eye_f64();
        let high = [e.x as f32, e.y as f32, e.z as f32];
        let low = [
            (e.x - high[0] as f64) as f32,
            (e.y - high[1] as f64) as f32,
            (e.z - high[2] as f64) as f32,
        ];
        (high, low)
    }

    /// Project a screen point onto an arbitrary world-space plane.
    ///
    /// The plane is defined by `plane_normal` (unit vector) and a `plane_point`
    /// that lies on it.  Returns the intersection of the view ray with the plane;
    /// falls back to `plane_point` when the ray is nearly parallel to the plane.
    pub fn pick_on_plane(
        &self,
        screen: Point,
        bounds: Rectangle,
        plane_normal: Vec3,
        plane_point: Vec3,
    ) -> Vec3 {
        // Delegate to the eye-relative f64 unproject so the cursor stays
        // precise at UTM-scale coordinates (the old full view_proj.inverse()
        // cancelled catastrophically in f32).
        self.unproject_on_plane_f64(screen, bounds, plane_normal, plane_point.as_dvec3())
            .as_vec3()
    }

    pub fn pick_on_target_plane(&self, screen: Point, bounds: Rectangle) -> Vec3 {
        self.pick_on_target_plane_f64(screen, bounds).as_vec3()
    }

    /// f64 variant of [`pick_on_plane`] — keeps the cursor precise at UTM-scale.
    pub fn pick_on_plane_f64(
        &self,
        screen: Point,
        bounds: Rectangle,
        plane_normal: Vec3,
        plane_point: glam::DVec3,
    ) -> glam::DVec3 {
        self.unproject_on_plane_f64(screen, bounds, plane_normal, plane_point)
    }

    /// f64 variant of [`pick_on_target_plane`].
    pub fn pick_on_target_plane_f64(&self, screen: Point, bounds: Rectangle) -> glam::DVec3 {
        let forward = (self.target.as_vec3() - self.eye()).normalize_or(Vec3::NEG_Z);
        self.unproject_on_plane_f64(screen, bounds, forward, self.target)
    }


    // ── ViewCube rotation matrix ───────────────────────────────────────────

    /// Returns the rotation matrix for the ViewCube.
    ///
    /// The camera quaternion maps canonical pose (+Z eye) → current view.
    /// The ViewCube needs the inverse so the cube stays world-aligned.
    /// Inverse of a unit quaternion = its conjugate.
    pub fn view_rotation_mat(&self) -> Mat4 {
        Mat4::from_quat(self.rotation.conjugate())
    }

    /// The camera's roll — rotation about the view axis, in radians — the
    /// inverse of the `roll` argument to [`yaw_pitch_to_quat`]. Recovered by
    /// removing the yaw/pitch frame from the live rotation, so a saved view can
    /// store its twist and round-trip it. Exact for a plan view (the twisted-
    /// UCS case); approximate after a free 3D orbit.
    pub fn roll(&self) -> f32 {
        let q_yp = yaw_pitch_to_quat(self.yaw, self.pitch, 0.0);
        let q_roll = q_yp.conjugate() * self.rotation;
        // q_roll is (nominally) a rotation about Z; extract its angle.
        2.0 * q_roll.z.atan2(q_roll.w)
    }

    // ── Navigation ────────────────────────────────────────────────────────

    /// Arcball orbit: drag delta (dx, dy) in screen pixels.
    pub fn orbit(&mut self, delta_x: f32, delta_y: f32) {
        if delta_x.abs() < 1e-6 && delta_y.abs() < 1e-6 {
            return;
        }

        let speed = 0.005_f32;
        let angle = (delta_x * delta_x + delta_y * delta_y).sqrt() * speed;

        // Screen drag → rotation axis: right drag = rotate around cam_up (Y),
        // down drag = rotate around cam_right (X). Negate so drag direction
        // matches intuitive "grab and spin" arcball behaviour.
        let screen_axis = vec3(-delta_y, -delta_x, 0.0).normalize_or_zero();

        let cam_right = self.rotation * Vec3::X;
        let cam_up = self.rotation * Vec3::Y;
        let world_axis = (cam_right * screen_axis.x + cam_up * screen_axis.y).normalize_or_zero();

        if world_axis.length_squared() < 1e-12 {
            return;
        }

        let delta_rot = Quat::from_axis_angle(world_axis, angle);
        self.rotation = (delta_rot * self.rotation).normalize();

        // Sync legacy yaw/pitch for hit-test functions.
        self.sync_yaw_pitch();
    }

    pub fn zoom(&mut self, delta: f32) {
        self.distance = (self.distance * (1.0 - delta * 0.1)).max(0.001);
    }

    /// World-space offset from `target` to the point under `screen` on the
    /// target plane. Computed in the camera frame (small numbers) and rotated
    /// to world — it never touches the large absolute target, so it stays
    /// precise at UTM-scale coordinates. For perspective this is the offset
    /// evaluated at the target plane (the correct pivot for zoom-to-cursor).
    fn cursor_offset_on_target_plane(&self, screen: Point, bounds: Rectangle) -> Vec3 {
        let ndc_x = (screen.x / bounds.width) * 2.0 - 1.0;
        let ndc_y = 1.0 - (screen.y / bounds.height) * 2.0;
        let aspect = bounds.width / bounds.height;
        let half_h = self.ortho_size();
        let half_w = half_h * aspect;
        let cam_right = self.rotation * Vec3::X;
        let cam_up = self.rotation * Vec3::Y;
        cam_right * (ndc_x * half_w) + cam_up * (ndc_y * half_h)
    }

    pub fn zoom_about_point(&mut self, screen: Point, bounds: Rectangle, delta: f32) {
        if bounds.width <= 0.0 || bounds.height <= 0.0 {
            self.zoom(delta);
            return;
        }

        // Keep the point under the cursor fixed by working with its offset
        // *relative to target* before and after the zoom. Both offsets are
        // small (camera-frame) numbers, so their difference is exact even at
        // UTM coordinates — the old absolute view_proj.inverse() picks each
        // carried ~0.5 m of f32 error that didn't cancel, making the whole
        // scene jump on every zoom step.
        let before = self.cursor_offset_on_target_plane(screen, bounds);
        self.zoom(delta);
        let after = self.cursor_offset_on_target_plane(screen, bounds);
        self.target += (before - after).as_dvec3();
    }

    /// Pan so the world point under the cursor tracks it: screen pixels are
    /// converted to world units via the ortho world-per-pixel scale of a
    /// viewport `viewport_height` pixels tall. Used by tiled panes where the
    /// pane height differs from the full canvas.
    pub fn pan_screen(&mut self, delta_x: f32, delta_y: f32, viewport_height: f32) {
        let wpp = if viewport_height > 0.0 {
            (2.0 * self.ortho_size()) / viewport_height
        } else {
            0.0
        };
        let cam_right = self.rotation * Vec3::X;
        let cam_up = self.rotation * Vec3::Y;
        self.target -= (cam_right * delta_x * wpp).as_dvec3();
        self.target += (cam_up * delta_y * wpp).as_dvec3();
    }

    pub fn fit_to_bounds(&mut self, min: Vec3, max: Vec3) {
        self.target = ((min + max) * 0.5).as_dvec3();
        let size = (max - min).length();
        self.distance = size * 1.5;
    }

    // ── ViewCube snap ─────────────────────────────────────────────────────

    /// Snap to a canonical view direction (called by ViewCubeSnap).
    /// `eye_dir` is the unit vector from the target toward the camera.
    ///
    /// Up vector resolution:
    ///  1. Take the current up.
    ///  2. Pick the world axis (±X, ±Y, ±Z) whose dot product with the
    ///     current up is highest — skipping any axis (anti-)parallel to
    ///     the new gaze direction.
    ///  3. Project that axis onto the plane ⊥ `new_eye` and use that as
    ///     the new up.
    ///
    /// Result: small tilts collapse onto the nearest world axis (so the
    /// view always lands cleanly aligned), while genuine flips of the
    /// up-sense (e.g. orbited upside-down) are preserved.
    pub fn snap_to_direction(&mut self, eye_dir: Vec3, ucs: glam::Mat4) {
        let new_eye = eye_dir.normalize_or(Vec3::Z);
        let cur_up = self.rotation * Vec3::Y;
        // Candidate up axes are the UCS axes, not world X/Y/Z, so a face snap
        // lands the view square to the user's coordinate system (in-plane roll
        // included). Identity `ucs` reproduces the world-aligned snap.
        let ux = ucs.transform_vector3(Vec3::X).normalize_or(Vec3::X);
        let uy = ucs.transform_vector3(Vec3::Y).normalize_or(Vec3::Y);
        let uz = ucs.transform_vector3(Vec3::Z).normalize_or(Vec3::Z);
        let cardinals = [ux, -ux, uy, -uy, uz, -uz];
        let mut best_score = f32::NEG_INFINITY;
        let mut best_up = uz;
        for axis in cardinals {
            // Skip axes (nearly) collinear with the new gaze — they can't
            // serve as up because the projection onto the plane would
            // vanish.
            if axis.dot(new_eye).abs() > 0.999 {
                continue;
            }
            let score = axis.dot(cur_up);
            if score > best_score {
                best_score = score;
                best_up = axis;
            }
        }
        // Project the chosen axis onto the plane ⊥ new_eye and normalize.
        let projected = best_up - new_eye * best_up.dot(new_eye);
        let new_up = projected.normalize_or(if new_eye.dot(uz).abs() < 0.99 {
            (uz - new_eye * uz.dot(new_eye)).normalize()
        } else {
            (uy - new_eye * uy.dot(new_eye)).normalize()
        });
        let new_right = new_up.cross(new_eye).normalize();
        // Camera rotation columns: [cam_x | cam_y | cam_z] where
        // cam_z = eye_dir (canonical "+Z is toward eye"), cam_y = up.
        let mat = glam::Mat3::from_cols(new_right, new_up, new_eye);
        self.rotation = Quat::from_mat3(&mat).normalize();
        self.sync_yaw_pitch();
    }

    // ── Internal helpers ───────────────────────────────────────────────────

    /// Derive yaw and pitch from the current quaternion for the ViewCube
    /// hit-test functions (hit_test / hover_id). These use yaw/pitch to
    /// compute the same rotation matrix as the shader, so they must match.
    fn sync_yaw_pitch(&mut self) {
        // Eye direction in world space (canonical eye dir is +Z).
        let eye_dir = self.rotation * Vec3::Z;
        // pitch: angle above/below the XY plane.
        self.pitch = eye_dir.z.clamp(-0.999, 0.999).asin();
        // yaw: atan2(x, y) matches from_rotation_z(yaw) used in view_rotation_mat.
        self.yaw = eye_dir.x.atan2(eye_dir.y);
    }
}

// ── Free helpers ───────────────────────────────────────────────────────────

/// Build a rotation quaternion from yaw (rotation around Z) and pitch
/// (tilt toward Z). Matches the coordinate convention of the ViewCube
/// so snap angles continue to work unchanged.
///
/// Convention (Z-up, Y-forward):
///   yaw   = 0          → camera looks along +Y axis (front view)
///   pitch = PI/2       → camera looks down -Z (top view)
///   pitch = 0          → camera in the XY plane
/// Build a rotation quaternion from yaw, pitch and roll.
/// Positive yaw rotates the view direction clockwise when seen from above (Z-up).
/// Roll rotates the camera around its own view axis (post-multiplied so it
/// composes after the yaw/pitch gaze direction is set).
pub fn yaw_pitch_to_quat(yaw: f32, pitch: f32, roll: f32) -> Quat {
    // +yaw so ViewCube faces match camera direction (FRONT at yaw=0 = +Y world axis).
    let q_yaw = Quat::from_rotation_z(yaw);
    let q_pitch = Quat::from_rotation_x(std::f32::consts::FRAC_PI_2 - pitch);
    let q_roll = Quat::from_rotation_z(roll);
    (q_yaw * q_pitch * q_roll).normalize()
}