bevy_flora 0.3.3

//! Bevy integration: components, the `FloraPlugin`, and the systems that
//! grow trees and rebuild their meshes.
//!
//! A tree entity carries [`ProceduralTree`] (its parameters) and [`TreeAge`].
//! Whenever either changes, [`rebuild_trees`] regenerates the meshes and keeps
//! two child entities (wood and leaves) in sync. Adding [`Growing`] advances
//! `TreeAge` every frame until the tree is mature.
//!
//! Performance: a growing tree rebuilds both meshes every frame; `Growing` is
//! meant for a few hero trees, not a forest.

use bevy::asset::{Assets, Handle};
use bevy::ecs::prelude::*;
use bevy::mesh::{Mesh, Mesh3d};
use bevy::pbr::{MeshMaterial3d, StandardMaterial};
use bevy::reflect::Reflect;
use bevy::render::render_resource::Face;
use bevy::camera::visibility::Visibility;
use bevy::time::Time;
use bevy::transform::components::Transform;

use crate::mesh::MeshData;
use crate::params::TreeParams;
use crate::pipeline::build_tree;

/// Parameters of a procedural tree. Changing it rebuilds the meshes.
#[derive(Component, Clone, Debug, PartialEq, Reflect)]
#[reflect(Component)]
#[require(TreeAge, Transform, Visibility)]
pub struct ProceduralTree(pub TreeParams);

/// Age of the tree in growth units (see [`crate::GrowthParams`]).
/// Defaults to `f32::INFINITY`: fully grown.
#[derive(Component, Clone, Copy, Debug, PartialEq, Reflect)]
#[reflect(Component)]
pub struct TreeAge(pub f32);

impl Default for TreeAge {
    fn default() -> Self {
        Self(f32::INFINITY)
    }
}

/// Advances [`TreeAge`] by `rate` age units per second until mature.
#[derive(Component, Clone, Copy, Debug, PartialEq, Reflect)]
#[reflect(Component)]
pub struct Growing {
    /// Age units added to [`TreeAge`] per second.
    pub rate: f32,
}

impl Default for Growing {
    fn default() -> Self {
        Self { rate: 1.0 }
    }
}

/// Sent after a tree's meshes were (re)built.
#[derive(Message, Clone, Copy, Debug)]
pub struct TreeGenerated {
    /// The tree entity whose meshes were rebuilt.
    pub entity: Entity,
    /// Current trunk height (full height × growth progress).
    pub height: f32,
    /// Trunk radius parameter.
    pub radius: f32,
}

/// Render state owned by the plugin for one tree entity.
#[derive(Component)]
pub struct TreeRender {
    trunk: Entity,
    /// `None` until the trunk first has geometry.
    trunk_mesh: Option<Handle<Mesh>>,
    trunk_material: Handle<StandardMaterial>,
    foliage: Option<(Entity, Handle<Mesh>)>,
    foliage_material: Handle<StandardMaterial>,
    /// Age after which rebuilding changes nothing.
    pub mature_at: f32,
}

impl TreeRender {
    /// Child entity carrying the wood mesh.
    pub fn trunk_entity(&self) -> Entity {
        self.trunk
    }

    /// Child entity carrying the leaf mesh, if any leaves are currently visible.
    pub fn foliage_entity(&self) -> Option<Entity> {
        self.foliage.as_ref().map(|(e, _)| *e)
    }
}

/// Marker on the wood child entity.
#[derive(Component)]
pub struct TreeTrunkMesh;

/// Marker on the leaves child entity.
#[derive(Component)]
pub struct TreeFoliageMesh;

/// Registers the tree components and the grow/rebuild systems.
pub struct FloraPlugin;

impl bevy::app::Plugin for FloraPlugin {
    fn build(&self, app: &mut bevy::app::App) {
        app.add_message::<TreeGenerated>()
            .register_type::<ProceduralTree>()
            .register_type::<TreeAge>()
            .register_type::<Growing>()
            .add_systems(bevy::app::Update, (grow_trees, rebuild_trees).chain());
    }
}

/// Share of diffuse light a leaf lets through to its other side, so leaves
/// turned away from the sun are lit from behind instead of near-black.
const LEAF_TRANSLUCENCY: f32 = 0.5;

fn material(base_color: bevy::color::Color) -> StandardMaterial {
    StandardMaterial {
        base_color,
        perceptual_roughness: 1.0,
        cull_mode: Some(Face::Back),
        ..Default::default()
    }
}

fn leaf_material(base_color: bevy::color::Color) -> StandardMaterial {
    StandardMaterial {
        diffuse_transmission: LEAF_TRANSLUCENCY,
        ..material(base_color)
    }
}

/// Advance the age of every [`Growing`] tree that already has render state.
pub fn grow_trees(time: Res<Time>, mut trees: Query<(&mut TreeAge, &Growing, &TreeRender)>) {
    let dt = time.delta_secs();
    for (mut age, growing, render) in &mut trees {
        let next = (age.0 + growing.rate * dt).min(render.mature_at);
        if next != age.0 {
            age.0 = next;
        }
    }
}

/// Rebuild meshes for trees whose parameters or age changed.
#[allow(clippy::type_complexity)]
pub fn rebuild_trees(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
    mut generated: MessageWriter<TreeGenerated>,
    mut trees: Query<
        (Entity, &ProceduralTree, &TreeAge, Option<&mut TreeRender>),
        Or<(Changed<ProceduralTree>, Changed<TreeAge>)>,
    >,
) {
    for (entity, tree, age, render) in &mut trees {
        let params = &tree.0;
        let out = build_tree(params, age.0);
        let trunk_progress = out.skeleton.nodes[0].progress;

        match render {
            None => {
                let trunk_material = materials.add(material(params.trunk_color));
                let foliage_material = materials.add(leaf_material(params.foliage.color));
                let trunk = commands
                    .spawn((
                        MeshMaterial3d(trunk_material.clone()),
                        TreeTrunkMesh,
                        Visibility::Hidden,
                        ChildOf(entity),
                    ))
                    .id();
                let mut trunk_mesh = None;
                sync_trunk(&mut commands, &mut meshes, trunk, &mut trunk_mesh, out.trunk);
                let foliage = (!out.foliage.is_empty()).then(|| {
                    let handle = meshes.add(out.foliage.into_bevy_mesh());
                    let child = commands
                        .spawn((
                            Mesh3d(handle.clone()),
                            MeshMaterial3d(foliage_material.clone()),
                            TreeFoliageMesh,
                            ChildOf(entity),
                        ))
                        .id();
                    (child, handle)
                });
                commands.entity(entity).insert(TreeRender {
                    trunk,
                    trunk_mesh,
                    trunk_material,
                    foliage,
                    foliage_material,
                    mature_at: out.mature_at,
                });
            }
            Some(mut render) => {
                render.mature_at = out.mature_at;
                let trunk_entity = render.trunk;
                sync_trunk(
                    &mut commands,
                    &mut meshes,
                    trunk_entity,
                    &mut render.trunk_mesh,
                    out.trunk,
                );
                if let Some(mut m) = materials.get_mut(&render.trunk_material) {
                    m.base_color = params.trunk_color;
                }
                if let Some(mut m) = materials.get_mut(&render.foliage_material) {
                    m.base_color = params.foliage.color;
                }

                match (&mut render.foliage, out.foliage.is_empty()) {
                    (Some((child, handle)), false) => {
                        let child = *child;
                        replace_mesh(&mut commands, &mut meshes, child, handle, out.foliage.into_bevy_mesh());
                    }
                    (None, false) => {
                        let handle = meshes.add(out.foliage.into_bevy_mesh());
                        let child = commands
                            .spawn((
                                Mesh3d(handle.clone()),
                                MeshMaterial3d(render.foliage_material.clone()),
                                TreeFoliageMesh,
                                ChildOf(entity),
                            ))
                            .id();
                        render.foliage = Some((child, handle));
                    }
                    (Some((child, _)), true) => {
                        commands.entity(*child).despawn();
                        render.foliage = None;
                    }
                    (None, true) => {}
                }
            }
        }

        generated.write(TreeGenerated {
            entity,
            height: params.trunk.height * trunk_progress,
            radius: params.trunk.radius,
        });
    }
}

/// Bring the trunk child in sync with `data`. An empty trunk (age 0) hides the
/// child and uploads nothing; the mesh asset is created the first time the
/// trunk has geometry.
fn sync_trunk(
    commands: &mut Commands,
    meshes: &mut Assets<Mesh>,
    child: Entity,
    handle: &mut Option<Handle<Mesh>>,
    data: MeshData,
) {
    if data.is_empty() {
        commands.entity(child).insert(Visibility::Hidden);
        return;
    }
    commands.entity(child).insert(Visibility::Inherited);
    match handle {
        Some(handle) => replace_mesh(commands, meshes, child, handle, data.into_bevy_mesh()),
        None => {
            let new = meshes.add(data.into_bevy_mesh());
            commands.entity(child).insert(Mesh3d(new.clone()));
            *handle = Some(new);
        }
    }
}

/// Overwrite the asset behind `handle` in place; if it was removed externally,
/// allocate a new one and re-point `child`'s `Mesh3d` at it.
fn replace_mesh(
    commands: &mut Commands,
    meshes: &mut Assets<Mesh>,
    child: Entity,
    handle: &mut Handle<Mesh>,
    mesh: Mesh,
) {
    if let Some(mut slot) = meshes.get_mut(&*handle) {
        *slot = mesh;
        return;
    }
    *handle = meshes.add(mesh);
    commands.entity(child).insert(Mesh3d(handle.clone()));
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::presets::TreePreset;
    use bevy::app::App;
    use bevy::asset::{AssetApp, AssetPlugin};

    fn app() -> App {
        let mut app = App::new();
        app.add_plugins((bevy::MinimalPlugins, AssetPlugin::default()));
        app.init_asset::<Mesh>();
        app.init_asset::<StandardMaterial>();
        app.add_plugins(FloraPlugin);
        app
    }

    #[test]
    fn spawns_children_and_drops_foliage_at_age_zero() {
        let mut app = app();
        let tree = app
            .world_mut()
            .spawn((ProceduralTree(TreePreset::Oak.params()), TreeAge(f32::INFINITY)))
            .id();
        app.update();

        {
            let world = app.world();
            let render = world.get::<TreeRender>(tree).expect("TreeRender inserted");
            assert!(render.foliage.is_some());
            assert_eq!(world.get::<Children>(tree).unwrap().len(), 2);
            let meshes = world.resource::<Assets<Mesh>>();
            let trunk = meshes.get(render.trunk_mesh.as_ref().unwrap()).unwrap();
            assert!(trunk.count_vertices() > 0);
            assert_eq!(world.get::<Visibility>(render.trunk_entity()), Some(&Visibility::Inherited));
            assert!(render.mature_at.is_finite());
        }

        app.world_mut().get_mut::<TreeAge>(tree).unwrap().0 = 0.0;
        app.update();
        {
            let world = app.world();
            let render = world.get::<TreeRender>(tree).unwrap();
            assert!(render.foliage.is_none());
            assert_eq!(world.get::<Children>(tree).unwrap().len(), 1);
            assert_eq!(world.get::<Visibility>(render.trunk_entity()), Some(&Visibility::Hidden));
        }

        // Back to mature: foliage child returns.
        app.world_mut().get_mut::<TreeAge>(tree).unwrap().0 = f32::INFINITY;
        app.update();
        assert_eq!(app.world().get::<Children>(tree).unwrap().len(), 2);
        let world = app.world();
        let render = world.get::<TreeRender>(tree).unwrap();
        assert_eq!(world.get::<Visibility>(render.trunk_entity()), Some(&Visibility::Inherited));
    }

    #[test]
    fn trunk_born_empty_gets_its_mesh_once_it_grows() {
        let mut app = app();
        let tree = app
            .world_mut()
            .spawn((ProceduralTree(TreePreset::Oak.params()), TreeAge(0.0)))
            .id();
        app.update();
        let trunk = {
            let world = app.world();
            let render = world.get::<TreeRender>(tree).unwrap();
            assert!(render.trunk_mesh.is_none());
            let trunk = render.trunk_entity();
            assert_eq!(world.get::<Visibility>(trunk), Some(&Visibility::Hidden));
            assert!(world.get::<Mesh3d>(trunk).is_none());
            trunk
        };

        app.world_mut().get_mut::<TreeAge>(tree).unwrap().0 = 2.0;
        app.update();
        let world = app.world();
        let render = world.get::<TreeRender>(tree).unwrap();
        let handle = render.trunk_mesh.as_ref().expect("mesh created once the trunk exists");
        assert!(world.resource::<Assets<Mesh>>().get(handle).unwrap().count_vertices() > 0);
        assert_eq!(world.get::<Mesh3d>(trunk).map(|m| &m.0), Some(handle));
        assert_eq!(world.get::<Visibility>(trunk), Some(&Visibility::Inherited));
    }

    #[test]
    fn growing_stops_at_maturity() {
        let mut app = app();
        let tree = app
            .world_mut()
            .spawn((
                ProceduralTree(TreePreset::Oak.params()),
                TreeAge(0.0),
                Growing { rate: 1.0e7 },
            ))
            .id();
        app.update(); // first build at age 0 (no TreeRender yet when grow runs)
        app.update(); // grows to mature_at
        let age = app.world().get::<TreeAge>(tree).unwrap().0;
        let mature_at = app.world().get::<TreeRender>(tree).unwrap().mature_at;
        assert_eq!(age, mature_at);
        app.update();
        assert_eq!(app.world().get::<TreeAge>(tree).unwrap().0, mature_at);
    }
}