Implement object drafting

Relates to #23.

crates/objects/src/draft.rs

@@ -0,0 +1,57 @@
+//! This module implements a Bevy plugin for drafting new objects on the map.
+//! An entity marked with a component [`Draft`] is automatically handled and
+//! visualized by the plugin.
+
+use bevy::prelude::*;
+use de_core::{objects::ObjectType, state::GameState};
+use iyes_loopless::prelude::*;
+
+use crate::ObjectCache;
+
+pub(crate) struct DraftPlugin;
+
+impl Plugin for DraftPlugin {
+    fn build(&self, app: &mut App) {
+        app.add_system(new_draft.run_in_state(GameState::Playing));
+    }
+}
+
+/// Bundle to spawn a construction draft.
+#[derive(Bundle)]
+pub struct DraftBundle {
+    object_type: ObjectType,
+    transform: Transform,
+    global_transform: GlobalTransform,
+    draft: Draft,
+}
+
+impl DraftBundle {
+    pub fn new(object_type: ObjectType, transform: Transform) -> Self {
+        Self {
+            object_type,
+            transform,
+            global_transform: transform.into(),
+            draft: Draft,
+        }
+    }
+}
+
+#[derive(Component)]
+pub struct Draft;
+
+#[derive(Component)]
+struct Ready;
+
+type NonReadyDrafts<'w, 's> =
+    Query<'w, 's, (Entity, &'static ObjectType), (With<Draft>, Without<Ready>)>;
+
+fn new_draft(mut commands: Commands, drafts: NonReadyDrafts, cache: Res<ObjectCache>) {
+    for (entity, object_type) in drafts.iter() {
+        commands
+            .entity(entity)
+            .insert(Ready)
+            .with_children(|parent| {
+                parent.spawn_scene(cache.get(*object_type).scene());
+            });
+    }
+}

crates/objects/src/lib.rs

@@ -5,12 +5,15 @@ use bevy::{app::PluginGroupBuilder, prelude::PluginGroup};
 use cache::CachePlugin;
 pub use cache::ObjectCache;
 pub use collider::{ColliderCache, ObjectCollider};
+use draft::DraftPlugin;
+pub use draft::{Draft, DraftBundle};
 pub use ichnography::{Ichnography, IchnographyCache};
 pub use spawner::SpawnBundle;
 use spawner::SpawnerPlugin;
 
 mod cache;
 mod collider;
+mod draft;
 mod ichnography;
 mod loader;
 mod spawner;
@@ -19,6 +22,6 @@ pub struct ObjectsPluginGroup;
 
 impl PluginGroup for ObjectsPluginGroup {
     fn build(&mut self, group: &mut PluginGroupBuilder) {
-        group.add(CachePlugin).add(SpawnerPlugin);
+        group.add(CachePlugin).add(SpawnerPlugin).add(DraftPlugin);
     }
 }