Mixamo animation support (#37)

This PR adds support for Mixamo FBX imports (via backend conversion to
glTF/glB) and some miscellaneous improvements to the animation systems.

### User-facing improvements
* Retargeting math has been fixed to eliminate jittering issues
* Retargeter can now handle animated bone translations when present
  (generally this is only used for root motion)

### Housekeeping / Code improvements

* Animation-related components and system logic have been moved to a
  dedicated `anim` module and `AnimPlugin`
* Retargeting stuff has been moved from the `bvh` module to
  `anim::retargeting`
* Component-based solution for marking an entity as an animation
  retargeting source makes it easy to extend the retargeting functionality
  to new types of source animations

### Limitations

Currently the code assumes that there will be at most one animation
source at a time. That single animation (if present) will be retargeted
to all other skeletons in the scene. A component-based solution for
directing a specific target skeleton to use a specific source animation
is possible, but will require some additional consideration around the
implementation design for the read-only "viewer" modes.

### Test animations:

* Hip-Hop Dancing (Mixamo): ?mode=viewer&mixamo=mocap/hip-hop-dancing.gltf
* Shuffle (MocapNET): ?mode=viewer&bvh=mocap/shuffle.bvh
* Scott (MocapNET): ?mode=viewer&bvh=mocap/scott.bvh
* Scott 1 (MocapNET): ?mode=viewer&bvh=mocap/scott1.bvh

studio/src/scene.rs

@@ -6,22 +6,18 @@ use bevy::{
         tonemapping::Tonemapping,
     },
     gltf::Gltf,
-    math::{vec2, Affine3A},
+    math::vec2,
     pbr::ShadowFilteringMethod,
     prelude::*,
-    render::{mesh::skinning::SkinnedMesh, primitives::Aabb, view::NoFrustumCulling},
+    render::primitives::Aabb,
     scene::InstanceId,
 };
 
-use space_editor::{
-    prelude::PrefabMarker,
-    space_prefab::{component::SceneAutoChild, editor_registry::EditorRegistryExt},
-};
+use space_editor::{prelude::PrefabMarker, space_prefab::component::SceneAutoChild};
 #[cfg(feature = "wasm")]
 use wasm_bindgen::prelude::wasm_bindgen;
 
 use crate::{
-    bvh::{Bvh, CommandsSpawnBvhExt},
     camera_controller::{CameraController, CameraControllerBundle},
     debug::DebugPoint,
     math::{Combinable, Extrema},
@@ -40,14 +36,7 @@ impl Plugin for ScenePlugin {
             .add_state::<SceneState>()
             .add_event::<LoadSceneEvent>()
             .add_systems(Startup, initialize)
-            .add_systems(
-                Update,
-                (
-                    spawn_test_bvh.run_if(resource_exists::<TestBvh>()), // TODO
-                    init_scene_loading,
-                )
-                    .in_set(SceneSpawnerSystem),
-            )
+            .add_systems(Update, init_scene_loading.in_set(SceneSpawnerSystem))
             .add_systems(
                 OnEnter(SceneState::Active),
                 (tag_scene_elements, frame_scene_in_view).in_set(SceneSpawnerSystem),
@@ -71,10 +60,6 @@ impl Plugin for ScenePlugin {
         //setup default light
         app.add_systems(Startup, minimal_scene_setup);
 
-        app.editor_registry::<BindPoseLocal>();
-        app.editor_registry::<BindPoseGlobal>();
-        app.editor_registry::<InvBindPose>();
-
         #[cfg(feature = "wasm")]
         app.add_systems(
             Update,
@@ -190,25 +175,8 @@ pub struct SceneData {
     pub scene_path: String,
 }
 
-#[derive(Component)]
-pub struct SkeletalJoint(pub Color);
-
 #[derive(Component)]
 pub struct SceneRoot;
-#[derive(Resource, Deref, DerefMut)]
-pub struct TestBvh(pub Handle<Bvh>); // TODO
-
-#[derive(Component, Clone, Copy, Debug, Default, Deref, DerefMut, Reflect)]
-#[reflect(Component)]
-pub struct BindPoseLocal(pub Transform);
-
-#[derive(Component, Clone, Copy, Debug, Default, Deref, DerefMut, Reflect)]
-#[reflect(Component)]
-pub struct BindPoseGlobal(pub Affine3A);
-
-#[derive(Component, Clone, Copy, Debug, Default, Deref, DerefMut, Reflect)]
-#[reflect(Component)]
-pub struct InvBindPose(pub Affine3A);
 
 fn initialize(mut cmd: Commands) {
     // Camera, graphics settings
@@ -242,23 +210,6 @@ fn initialize(mut cmd: Commands) {
     ));
 }
 
-// TODO
-fn spawn_test_bvh(
-    mut commands: Commands,
-    mut er_bvh_events: EventReader<AssetEvent<Bvh>>,
-    r_bvh: Res<TestBvh>,
-) {
-    for event in er_bvh_events.read() {
-        if matches!(event, AssetEvent::LoadedWithDependencies { .. }) {
-            commands.spawn_bvh_with_transform(
-                &r_bvh.0,
-                Transform::from_scale(Vec3::splat(0.06))
-                    .with_translation(Vec3::new(0., 1.0, 0.524)),
-            );
-        }
-    }
-}
-
 fn init_scene_loading(mut cmd: Commands, mut er: EventReader<LoadSceneEvent>) {
     if let Some(id) = er.read().last() {
         info!("Loading scene: {}", id.0);
@@ -299,8 +250,6 @@ fn tag_scene_elements(
             Without<NoMeshElement>,
         ),
     >,
-    q_skinned_meshes: Query<(Entity, &SkinnedMesh), Without<InitedKointSkinnedMesh>>,
-    mut q_xforms: ParamSet<(TransformHelper, Query<&Transform>)>,
     mesh_entities: Query<Entity, With<Handle<Mesh>>>,
 ) {
     for (e, children) in q_named_non_primitives.iter() {
@@ -317,24 +266,6 @@ fn tag_scene_elements(
             cmd.entity(e).insert(NoMeshElement);
         }
     }
-
-    for (ent, skinned_mesh) in q_skinned_meshes.iter() {
-        cmd.entity(ent)
-            .insert(NoFrustumCulling)
-            .insert(InitedKointSkinnedMesh);
-
-        for &joint in skinned_mesh.joints.iter() {
-            let global_bind_pose = q_xforms.p0().compute_global_transform(joint).unwrap();
-            let local_bind_pose = *q_xforms.p1().get(joint).unwrap();
-
-            cmd.entity(joint).insert((
-                SkeletalJoint(Color::BLACK),
-                BindPoseLocal(local_bind_pose),
-                BindPoseGlobal(global_bind_pose.affine()),
-                InvBindPose(global_bind_pose.affine().inverse()),
-            ));
-        }
-    }
 }
 
 fn frame_scene_in_view(