BVH animation loading / retargeting (#25)

This PR adds support for BVH animation files, with a custom animation
player and retargeting solution for our Blender Rigify-based skeletal
meshes.

---------

Co-authored-by: Brooks Palin <brookspalin710@gmail.com>

studio/src/debug.rs

@@ -7,7 +7,9 @@ use bevy_mod_picking::debug::DebugPickingMode;
 use crate::{
     camera_controller::{CameraController, CameraMotionSystem},
     input::{Action, InputAction, Lifecycle},
-    is_editor, MainCamera,
+    is_editor,
+    scene::SkeletalJoint,
+    MainCamera,
 };
 
 #[derive(Resource, Deref, DerefMut)]
@@ -40,7 +42,7 @@ impl Plugin for DebugPlugin {
                         .run_if(is_editor)
                         .run_if(resource_changed::<DebugMode>()),
                     update_gizmo_line_thickness,
-                    (draw_world_axes, draw_debug_points)
+                    (draw_world_axes, draw_debug_points, draw_skeletal_joints)
                         .after(CameraMotionSystem)
                         .run_if(is_debug_mode),
                 ),
@@ -110,6 +112,34 @@ fn draw_debug_points(
     }
 }
 
+fn draw_skeletal_joints(
+    mut gizmos: Gizmos,
+    q_joints: Query<(&GlobalTransform, Option<&Parent>, &SkeletalJoint)>,
+) {
+    for (world_xform, parent, joint) in q_joints.iter() {
+        let (_, rotation, xlation) = world_xform.to_scale_rotation_translation();
+
+        if let Some((parent_xform, _, _)) = parent.and_then(|parent| q_joints.get(**parent).ok()) {
+            let parent_xlation = parent_xform.translation();
+            let bone_len = Vec3::distance(xlation, parent_xlation);
+            let joint_radius = f32::min(0.01, bone_len / 6.);
+
+            gizmos.sphere(xlation, rotation, joint_radius, joint.0);
+            gizmos.line(xlation, parent_xlation, joint.0);
+
+            let local_x = world_xform.right() * 0.05;
+            let local_y = world_xform.up() * 0.05;
+            let local_z = world_xform.back() * 0.05;
+
+            gizmos.line(xlation, xlation + local_x, Color::RED);
+            gizmos.line(xlation, xlation + local_y, Color::GREEN);
+            gizmos.line(xlation, xlation + local_z, Color::BLUE);
+        } else {
+            gizmos.sphere(xlation, rotation, 0.01, joint.0);
+        }
+    }
+}
+
 #[rustfmt::skip]
 #[allow(dead_code)]
 pub fn write_mat3(w: &mut impl fmt::Write, m: &Mat3) -> fmt::Result {