//! Mouse (Buttons)         | Touch (Fingers)         | Keyboard | Operation
//! ----------------------- | ----------------------- | -------- | ---------------------------------
//! Left Press + Drag       | One + Drag              | `ijkl`   | Orbits around target.
//! ↳ at trackball's border | Two + Roll              | `uo`     | Rolls about view direction.
//! Middle Press + Drag     | Any + Drag + Left Shift | `↑←↓→`   | First-person mode.
//! Right Press + Drag      | Two + Drag              | `esdf`   | Slides trackball on focus plane.
//!                    |                    | `gv`     | Slides trackball in/out.
//! Scroll In/Out           | Two + Pinch Out/In      | `hn`     | Scales distance zooming in/out.
//! Left Press + Release    | Any + Release           |     | Slides to cursor/finger position.
//!                    |                    | `m`      | Toggle `esdf`/`wasd` mapping.
//!                    |                    | `p`      | Toggle orthographic/perspective.
//!                    |                    | `Enter`  | Reset camera transform.
//!
//! A simple 3D scene with light shining over a cube sitting on a plane and a trackball camera
//! waiting for your input to orbit around.
//!
//! This is an alternative trackball technique using exponential map and parallel transport to
//! preserve distances and angles for inducing coherent and intuitive trackball rotations. For
//! instance, displacements on straight radial lines through the screen's center are carried to arcs
//! of the same length on great circles of the trackball (e.g., dragging the mouse along an eights
//! of the trackball's circumference rolls the camera by 360/8=45 degrees, dragging the mouse from
//! the screen's center to its further edge *linearly* rotates the camera by 1 [radian], where the
//! trackball's diameter is the maximum of the screen's width and height). This is in contrast to
//! state-of-the-art techniques using orthogonal projection which distorts radial distances further
//! away from the screen's center (e.g., the rotation accelerates towards the edge).
//!
//! [radian]: https://en.wikipedia.org/wiki/Radian

use bevy::prelude::*;
use bevy_trackball::prelude::*;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins.set(WindowPlugin {
            primary_window: Some(Window {
                canvas: Some("#bevy".to_owned()),
                ..default()
            }),
            ..default()
        }))
        .add_plugins(TrackballPlugin)
        .add_systems(Startup, setup)
        .run();
}

/// set up a simple 3D scene
fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    // circular base
    commands.spawn((
        Mesh3d(meshes.add(Circle::new(4.0))),
        MeshMaterial3d(materials.add(Color::WHITE)),
        Transform::from_rotation(Quat::from_rotation_x(-std::f32::consts::FRAC_PI_2)),
    ));
    // cube
    commands.spawn((
        Mesh3d(meshes.add(Cuboid::new(1.0, 1.0, 1.0))),
        MeshMaterial3d(materials.add(Color::srgb_u8(124, 144, 255))),
        Transform::from_xyz(0.0, 0.5, 0.0),
    ));
    // light
    commands.spawn((
        PointLight {
            shadow_maps_enabled: true,
            ..default()
        },
        Transform::from_xyz(4.0, 8.0, 4.0),
    ));
    // camera
    commands.spawn((
        TrackballController::default(),
        TrackballCamera::look_at(Vec3::new(-2.5, 4.5, 9.0), Vec3::Y * 0.5, Vec3::Y),
        Camera3d::default(),
    ));
}