physics: fix drag, volume, density, and buoyancy

docs/devlog.md

@@ -2,7 +2,87 @@
 
 ## 2024-11-26
 
-- Added a `GasMonitor` to the UI for displaying the gas properties in real time.
+I added a `GasMonitor` to the UI for displaying the gas properties in real time.
+With that in place, I can now notice that the balloon's density is reported as
+NaN, which is probably why buoyancy is not working. I think I found the bug. The
+density was not being updated in the system that updates gas properties from
+the atmosphere. Fixed that, but buoyancy is still pegged at 0. Curious, the
+buoyant system was querying `With<SimulatedBody>`, maybe something is messed up
+with the query because this system is definitely running every frame. A default
+`ForceBundle` is supposed to be added to the balloon when it is added to the
+world, so I'm curious why the buoyancy component is not being added. The
+`Weight` component is being added... Ah, the buoyancy system is also querying
+`Volume` components, weight is not. Maybe the query isn't turning up the bodies
+because the `Volume` component is not being added? With Bevy 0.15 we can enforce
+such a thing with the `#[require(x)]` attribute. Turns out there's no system
+that updates the volume because I wanted to calculate it from the balloon's
+primitive shape. I'll change buoyancy to query the balloon and get its volume
+instead. That fixed the buoyancy system so it runs, but the force results might
+not be correct.
+
+```sh
+INFO yahs::simulator::forces: Weight [0, -5.1347504, 0]
+INFO yahs::simulator::forces: Buoyancy [0, 3888.388, 0]
+INFO yahs::simulator::forces: Drag [NaN, NaN, NaN]
+```
+
+I traced the drag force NaN to the drag area returning nan from
+`balloon.shape.diameter()` at startup before the shape is set up.
+
+```sh
+ INFO yahs::simulator::forces::aero: balloon shape: Sphere { radius: NaN }
+ERROR yahs::simulator::forces: Drag has NaN magnitude!
+ERROR yahs::simulator::forces: Buoyancy has NaN magnitude!
+ INFO yahs::simulator::forces::aero: balloon shape: Sphere { radius: 4.2564797 }
+ INFO yahs::simulator::forces::aero: balloon shape: Sphere { radius: 4.2810054 }
+ INFO yahs::simulator::forces::aero: balloon shape: Sphere { radius: 4.2810054 }
+```
+
+I enforced that the mesh volumes are updated before the forces are calculated,
+but there might be a few frames at the beginning where the Mesh isn't
+initialized yet. Maybe it works a little differently because it's an asset?
+I noticed that the balloon was being spawned after the ground plane, and scene
+setup was not constrained to run in any system set. So the forces probably ran
+before the scene was done loading. I added a few conditions:
+
+- The app starts in the `Loading` state.
+- The scene advances to the `Running` state when it is done setting up the scene.
+- The physics systems only run when the app is in the `Running` state.
+
+Weird, something else is going on. The balloon shape is a real number when it is
+spawned and before the forces run, but when the forces run it is NaN.
+
+```sh
+ INFO bevy_winit::system: Creating new window "🎈" (0v1#4294967296)
+ INFO yahs::app3d::scene: sphere: Sphere { radius: 0.5 }
+ INFO bevy_dev_tools::states: yahs::simulator::core::SimState transition: Some(Loading) => Some(Running)
+ INFO yahs::app3d::scene: sim state: Res(State(Running))
+ INFO yahs::app3d::scene: balloon spawned: 19v1 Balloon { material_properties: BalloonMaterial { name: "Latex", max_temperature: 373.0, density: 920.0, emissivity: 0.9, absorptivity: 0.9, thermal_conductivity: 0.13, specific_heat: 2000.0, poissons_ratio: 0.5, elasticity: 10000000.0, max_strain: 0.8, max_stress: 500000.0, thickness: 0.0001 }, shape: Sphere { radius: 0.5 } } Sphere { radius: 0.5 }
+ INFO yahs::simulator::forces::aero: balloon shape: Sphere { radius: NaN }
+ERROR yahs::simulator::forces: Drag has NaN magnitude!
+ERROR yahs::simulator::forces: Buoyancy has NaN magnitude!
+ WARN avian3d::collision::narrow_phase: 18v1#4294967314 (Ground) and 19v1#4294967315 (Balloon) are overlapping at spawn, which can result in explosive behavior.
+ INFO yahs::app3d::scene: sim state: Res(State(Running))
+ INFO yahs::simulator::forces::aero: balloon shape: Sphere { radius: 4.2564797 }
+ INFO yahs::app3d::scene: sim state: Res(State(Running))
+ INFO yahs::simulator::forces::aero: balloon shape: Sphere { radius: 4.2810054 }
+ INFO yahs::app3d::scene: sim state: Res(State(Running))
+ INFO yahs::simulator::forces::aero: balloon shape: Sphere { radius: 4.2810054 }
+```
+
+I noticed that density is initialized to NaN with the ideal gas and the volume
+of the balloon is derived from the ideal gas volume. The volume is calculated
+before the force, so that explains where this NaN is coming from.
+
+Found it. Ideal gas law has pressure in the denominator of the volume equation.
+Pressure initializes to zero by default, so the volume is NaN. Changing the
+default from zero to the standard atmospheric pressure fixes that issue.
+
+I think the sim was crashing because it kept defaulting to use way too much
+mass in the balloon. I added `with_volume()` to the ideal gas to fix that, so we
+can spawn the balloon with a known volume at the default density.
+
+It works!
 
 ## 2024-11-24
 

src/app3d/scene.rs

@@ -7,7 +7,10 @@ pub struct ScenePlugin;
 
 impl Plugin for ScenePlugin {
     fn build(&self, app: &mut App) {
-        app.add_systems(Startup, (simple_scene, spawn_balloon));
+        app.add_systems(Startup, (spawn_balloon, simple_scene));
+        // app.add_systems(PostStartup, |mut commands: Commands| {
+        //     commands.set_state(SimState::Running);
+        // });
     }
 }
 
@@ -35,7 +38,7 @@ fn simple_scene(
     ));
 }
 
-pub fn spawn_balloon(
+fn spawn_balloon(
     mut commands: Commands,
     mut meshes: ResMut<Assets<Mesh>>,
     mut materials: ResMut<Assets<StandardMaterial>>,
@@ -57,7 +60,7 @@ pub fn spawn_balloon(
                 material_properties: BalloonMaterial::default(),
                 shape: sphere,
             },
-            gas: IdealGas::new(species),
+            gas: IdealGas::new(species).with_mass(Mass::new(0.01)),
         },
         RigidBody::Dynamic,
         Collider::sphere(sphere.radius),

src/app3d/ui/core.rs

@@ -51,7 +51,7 @@ fn toggle_pause(
         match sim_state.as_ref().get() {
             SimState::Stopped => next_state.set(SimState::Running),
             SimState::Running => next_state.set(SimState::Stopped),
-            _ => ()
+            _ => next_state.set(SimState::Running)
         }
     }
 }

src/app3d/ui/dev_tools.rs

@@ -15,7 +15,7 @@ use bevy::{
 };
 use iyes_perf_ui::prelude::*;
 
-use crate::app3d::controls::KeyBindingsConfig;
+use crate::{app3d::controls::KeyBindingsConfig, simulator::SimState};
 
 pub(super) fn plugin(app: &mut App) {
     // Toggle the debug overlay for UI.
@@ -36,6 +36,8 @@ pub(super) fn plugin(app: &mut App) {
     app.add_observer(spawn_perf_ui);
     app.add_observer(despawn_perf_ui);
 
+    app.add_systems(Update, log_transitions::<SimState>);
+
     // Wireframe doesn't work on WASM
     #[cfg(not(target_arch = "wasm32"))]
     app.add_systems(Update, toggle_debug_ui);

src/app3d/ui/monitors.rs

@@ -10,6 +10,7 @@ use crate::simulator::{
     forces::{Buoyancy, Drag, Force, Weight},
     SimState, SimulatedBody,
     ideal_gas::IdealGas,
+    balloon::Balloon,
 };
 
 pub struct MonitorsPlugin;
@@ -21,8 +22,6 @@ impl Plugin for MonitorsPlugin {
         app.add_perf_ui_simple_entry::<ForceMonitor>();
         app.add_perf_ui_simple_entry::<GasMonitor>();
         app.add_systems(Startup, spawn_monitors);
-        app.add_systems(Update, update_force_monitor_values);
-        app.init_resource::<ForceMonitorResource>();
     }
 }
 
@@ -62,7 +61,7 @@ impl Default for SimStateMonitor {
             label: String::new(),
             display_units: false,
             threshold_highlight: Some(10.0),
-            color_gradient: ColorGradient::new_preset_gyr(0.0, 10.0, 100.0).unwrap(),
+            color_gradient: ColorGradient::new_preset_gyr(0.0, 5.0, 10.0).unwrap(),
             digits: 7,
             precision: 0,
             sort_key: iyes_perf_ui::utils::next_sort_key(),
@@ -88,9 +87,9 @@ impl PerfUiEntry for SimStateMonitor {
 
     fn format_value(&self, value: &Self::Value) -> String {
         match value {
+            SimState::Loading => String::from("Loading"),
             SimState::Running => String::from("Running"),
             SimState::Stopped => String::from("Stopped"),
-            SimState::Anomaly => String::from("ANOMALY")
         }
     }
 
@@ -120,7 +119,7 @@ impl PerfUiEntry for SimStateMonitor {
         match *value {
             SimState::Running => self.color_gradient.get_color_for_value(0.0),
             SimState::Stopped => self.color_gradient.get_color_for_value(10.0),
-            _ => self.color_gradient.get_color_for_value(100.0),
+            _ => self.color_gradient.get_color_for_value(5.0),
         }
     }
 
@@ -132,25 +131,6 @@ impl PerfUiEntry for SimStateMonitor {
     }
 }
 
-#[derive(Resource, Reflect, Default)]
-struct ForceMonitorResource {
-    pub weight: Vec3,
-    pub buoyancy: Vec3,
-    pub drag: Vec3,
-}
-
-fn update_force_monitor_values(
-    mut force_resource: ResMut<ForceMonitorResource>,
-    forces: Query<(&Weight, &Buoyancy, &Drag), With<SimulatedBody>>,
-) {
-    for (weight, bouyancy, drag) in forces.iter() {
-        // assume there's only one simulated body for now
-        force_resource.weight = weight.force();
-        force_resource.buoyancy = bouyancy.force();
-        force_resource.drag = drag.force();
-    }
-}
-
 #[derive(Component)]
 struct ForceMonitor {
     /// The label text to display, to allow customization
@@ -179,15 +159,15 @@ impl Default for ForceMonitor {
             threshold_highlight: Some(10.0),
             color_gradient: ColorGradient::new_preset_gyr(0.0, 10.0, 100.0).unwrap(),
             digits: 5,
-            precision: 2,
+            precision: 3,
             sort_key: iyes_perf_ui::utils::next_sort_key(),
         }
     }
 }
 
 impl PerfUiEntry for ForceMonitor {
     type Value = (f32, f32, f32);
-    type SystemParam = SRes<ForceMonitorResource>; // FIXME: use &(dyn Force + 'static) instead
+    type SystemParam = SQuery<(&'static Weight, &'static Buoyancy, &'static Drag), With<SimulatedBody>>;
 
     fn label(&self) -> &str {
         if self.label.is_empty() {
@@ -217,13 +197,16 @@ impl PerfUiEntry for ForceMonitor {
 
     fn update_value(
         &self,
-        force_resource: &mut <Self::SystemParam as SystemParam>::Item<'_, '_>,
+        force_resources: &mut <Self::SystemParam as SystemParam>::Item<'_, '_>,
     ) -> Option<Self::Value> {
-        Some((
-            force_resource.weight.length(),
-            force_resource.buoyancy.length(),
-            force_resource.drag.length(),
-        ))
+        for (weight, buoyancy, drag) in force_resources.iter() {
+            return Some((
+                weight.force().y,
+                buoyancy.force().y,
+                drag.force().y,
+            ))
+        }
+        None
     }
 
     // (optional) We should add a width hint, so that the displayed
@@ -277,7 +260,7 @@ impl Default for GasMonitor {
 
 impl PerfUiEntry for GasMonitor {
     type Value = (f32, f32, f32, f32, f32, String);
-    type SystemParam = SQuery<&'static IdealGas>;
+    type SystemParam = SQuery<(&'static Balloon, &'static IdealGas)>;
 
     fn label(&self) -> &str {
         if self.label.is_empty() {
@@ -309,21 +292,21 @@ impl PerfUiEntry for GasMonitor {
             mass.push_str(" kg");
             species.push_str("");
         }
-        format!("{}\n{}\n{}\n{}\n{}\n{}", volume, pressure, temperature, density, mass, species)
+        format!("{}\n{}\n{}\n{}\n{}\n{}", species, volume, pressure, temperature, density, mass)
     }
 
     fn update_value(
         &self,
-        gas: &mut <Self::SystemParam as SystemParam>::Item<'_, '_>,
+        items: &mut <Self::SystemParam as SystemParam>::Item<'_, '_>,
     ) -> Option<Self::Value> {
-        let instance = gas.get_single().unwrap();
+        let (balloon, gas) = items.get_single().unwrap();
         Some((
-            instance.volume().m3(),
-            instance.pressure.kilopascals(),
-            instance.temperature.kelvin(),
-            instance.density.kilograms_per_cubic_meter(),
-            instance.mass.value(),
-            instance.species.name.clone(),
+            balloon.shape.volume(),
+            gas.pressure.kilopascals(),
+            gas.temperature.kelvin(),
+            gas.density.kilograms_per_cubic_meter(),
+            gas.mass.value(),
+            gas.species.name.clone(),
         ))
     }