Make the iter_combinators examples more pretty (#3075)

# Objective

- More colours

## Solution

- Various changes
- Would have a video here, but don't have an easy way to record one before I go to sleep
- I intend to additionally change the distribution of the satellites, to be more uniform in space.

examples/ecs/iter_combinations.rs

@@ -1,4 +1,4 @@
-use bevy::{core::FixedTimestep, prelude::*};
+use bevy::{core::FixedTimestep, pbr::AmbientLight, prelude::*, render::camera::Camera};
 use rand::{thread_rng, Rng};
 
 #[derive(Debug, Hash, PartialEq, Eq, Clone, StageLabel)]
@@ -10,6 +10,10 @@ fn main() {
     App::new()
         .insert_resource(Msaa { samples: 4 })
         .add_plugins(DefaultPlugins)
+        .insert_resource(AmbientLight {
+            brightness: 0.03,
+            ..Default::default()
+        })
         .add_startup_system(generate_bodies)
         .add_stage_after(
             CoreStage::Update,
@@ -19,11 +23,12 @@ fn main() {
                 .with_system(interact_bodies)
                 .with_system(integrate),
         )
+        .add_system(look_at_star)
+        .insert_resource(ClearColor(Color::BLACK))
         .run();
 }
 
 const GRAVITY_CONSTANT: f32 = 0.001;
-const SOFTENING: f32 = 0.01;
 const NUM_BODIES: usize = 100;
 
 #[derive(Component, Default)]
@@ -32,6 +37,8 @@ struct Mass(f32);
 struct Acceleration(Vec3);
 #[derive(Component, Default)]
 struct LastPos(Vec3);
+#[derive(Component)]
+struct Star;
 
 #[derive(Bundle, Default)]
 struct BodyBundle {
@@ -52,33 +59,33 @@ fn generate_bodies(
         subdivisions: 3,
     }));
 
-    let pos_range = 1.0..15.0;
     let color_range = 0.5..1.0;
     let vel_range = -0.5..0.5;
 
     let mut rng = thread_rng();
     for _ in 0..NUM_BODIES {
-        let mass_value_cube_root: f32 = rng.gen_range(0.5..4.0);
-        let mass_value: f32 = mass_value_cube_root * mass_value_cube_root * mass_value_cube_root;
+        let radius: f32 = rng.gen_range(0.1..0.7);
+        let mass_value = radius.powi(3) * 10.;
 
         let position = Vec3::new(
             rng.gen_range(-1.0..1.0),
             rng.gen_range(-1.0..1.0),
             rng.gen_range(-1.0..1.0),
         )
         .normalize()
-            * rng.gen_range(pos_range.clone());
+            * rng.gen_range(0.2f32..1.0).powf(1. / 3.)
+            * 15.;
 
         commands.spawn_bundle(BodyBundle {
             pbr: PbrBundle {
                 transform: Transform {
                     translation: position,
-                    scale: Vec3::splat(mass_value_cube_root * 0.1),
+                    scale: Vec3::splat(radius),
                     ..Default::default()
                 },
                 mesh: mesh.clone(),
                 material: materials.add(
-                    Color::rgb_linear(
+                    Color::rgb(
                         rng.gen_range(color_range.clone()),
                         rng.gen_range(color_range.clone()),
                         rng.gen_range(color_range.clone()),
@@ -101,29 +108,40 @@ fn generate_bodies(
     }
 
     // add bigger "star" body in the center
+    let star_radius = 1.;
     commands
         .spawn_bundle(BodyBundle {
             pbr: PbrBundle {
-                transform: Transform {
-                    scale: Vec3::splat(0.5),
-                    ..Default::default()
-                },
+                transform: Transform::from_scale(Vec3::splat(star_radius)),
                 mesh: meshes.add(Mesh::from(shape::Icosphere {
                     radius: 1.0,
                     subdivisions: 5,
                 })),
-                material: materials.add((Color::ORANGE_RED * 10.0).into()),
+                material: materials.add(StandardMaterial {
+                    base_color: Color::ORANGE_RED,
+                    emissive: (Color::ORANGE_RED * 2.),
+                    ..Default::default()
+                }),
                 ..Default::default()
             },
-            mass: Mass(1000.0),
+            mass: Mass(500.0),
             ..Default::default()
         })
-        .insert(PointLight {
-            color: Color::ORANGE_RED,
-            ..Default::default()
+        .insert(Star)
+        .with_children(|p| {
+            p.spawn_bundle(PointLightBundle {
+                point_light: PointLight {
+                    color: Color::WHITE,
+                    intensity: 400.0,
+                    range: 100.0,
+                    radius: star_radius,
+                    ..Default::default()
+                },
+                ..Default::default()
+            });
         });
     commands.spawn_bundle(PerspectiveCameraBundle {
-        transform: Transform::from_xyz(0.0, 10.5, -20.0).looking_at(Vec3::ZERO, Vec3::Y),
+        transform: Transform::from_xyz(0.0, 10.5, -30.0).looking_at(Vec3::ZERO, Vec3::Y),
         ..Default::default()
     });
 }
@@ -136,7 +154,7 @@ fn interact_bodies(mut query: Query<(&Mass, &GlobalTransform, &mut Acceleration)
         let delta = transform2.translation - transform1.translation;
         let distance_sq: f32 = delta.length_squared();
 
-        let f = GRAVITY_CONSTANT / (distance_sq * (distance_sq + SOFTENING).sqrt());
+        let f = GRAVITY_CONSTANT / distance_sq;
         let force_unit_mass = delta * f;
         acc1.0 += force_unit_mass * *m2;
         acc2.0 -= force_unit_mass * *m1;
@@ -156,3 +174,16 @@ fn integrate(mut query: Query<(&mut Acceleration, &mut Transform, &mut LastPos)>
         transform.translation = new_pos;
     }
 }
+
+fn look_at_star(
+    mut camera: Query<&mut Transform, (With<Camera>, Without<Star>)>,
+    star: Query<&Transform, With<Star>>,
+) {
+    let mut camera = camera.single_mut();
+    let star = star.single();
+    let new_rotation = camera
+        .looking_at(star.translation, Vec3::Y)
+        .rotation
+        .lerp(camera.rotation, 0.1);
+    camera.rotation = new_rotation;
+}