Studio Headless Mode (#36)

This PR adds the capaibility to run Stroyteller studio from the command
line, rendering the result to images. This is the basic functionality,
and there are somethings that I am saving for later when we make this a
more fully fledged feature.

Limitations:
- Right now, you cannot do image output resolutions that aren't 2^n.
This is a bug I plan on tackling later.

If you have questions on how the command line works, use the --help
argument.

Let me know what you think!

---------

Co-authored-by: Danny McGee <dannymcgee@gmail.com>

studio/src/bvh/mod.rs

@@ -24,6 +24,7 @@ pub struct BvhPlugin;
 impl Plugin for BvhPlugin {
     fn build(&self, app: &mut App) {
         app.init_asset::<Bvh>()
+            .add_event::<BvhAnimCompleteEvent>()
             .register_asset_loader(BvhLoader)
             // FIXME: Need to add a state for this module (similar to scene
             //        module's `SceneState`) to manage the order/frequency at
@@ -106,6 +107,7 @@ fn compute_inverse_bindposes(
 pub fn animate_bvh(
     mut q_bvh_anims: Query<(&mut BvhAnim, &Children)>,
     mut q_bvh_joints: Query<JointQuery, Without<BvhAnim>>,
+    mut bvh_event_writer: EventWriter<BvhAnimCompleteEvent>,
     r_bvh_assets: Res<Assets<Bvh>>,
     r_time: Res<Time>,
 ) {
@@ -122,6 +124,9 @@ pub fn animate_bvh(
 
             if anim.timer.just_finished() {
                 anim.frame = (anim.frame + 1) % bvh_len;
+                if anim.frame == 0 {
+                    bvh_event_writer.send(BvhAnimCompleteEvent);
+                }
             }
 
             anim.timer.percent()
@@ -204,6 +209,16 @@ fn lerp_frames<T: ReadOnlyWorldQuery>(
     }
 }
 
+//==============================================================================
+//                        Bvh Anim Events
+//==============================================================================
+
+// This may seem weird, but this is for the Headless mode to
+// know when to stop recording.
+
+#[derive(Event)]
+pub struct BvhAnimCompleteEvent;
+
 //==============================================================================
 //                        Bvh Anim Component
 //==============================================================================