first attempt at jovian ring with shader

assets/shaders/jupiters_rings.wgsl

@@ -0,0 +1,33 @@
+#import bevy_pbr::{
+    mesh_view_bindings::globals,
+    forward_io::VertexOutput,
+}
+
+@group(2) @binding(0) var<uniform> ring_radius: f32;
+@group(2) @binding(1) var<uniform> jupiter_radius: f32;
+
+@fragment
+fn fragment(in: VertexOutput) -> @location(0) vec4<f32> {
+    let jupiter_percent = jupiter_radius / ring_radius;
+    let color = vec3<f32>(0.3, 0.3, 0.3);
+    var alpha = 0.01;
+    let r = distance(in.uv, vec2<f32>(0.5));
+
+    alpha *= (sin(11*r / 0.71 * 3.1415) + 1) / 2;
+    alpha *= (cos(r / 0.72 * 3.1415) + 1) / 2;
+
+    if in.uv[0] < 0.5 {
+        let dist = (0.5 - in.uv[0]) * 2.0; // 0.0=jupiter's center, 1.0=edge of the ring
+        let side_dist = abs(in.uv[1] - 0.5);
+
+        let cutoff = 0.5 * jupiter_percent * cos(dist);
+        if side_dist < cutoff {
+            return vec4<f32>(color, 0.0);
+        }
+        let fuzzy_boundary = 0.01;
+        if side_dist < cutoff + fuzzy_boundary {
+            return vec4<f32>(color, alpha * (side_dist - cutoff) / fuzzy_boundary);
+        }
+    }
+    return vec4<f32>(color, alpha);
+}

assets/shaders/testshader.wgsl

@@ -1,22 +0,0 @@
-#import bevy_pbr::{
-    mesh_view_bindings::globals,
-    forward_io::VertexOutput,
-}
-
-@fragment
-fn fragment(in: VertexOutput) -> @location(0) vec4<f32> {
-    let speed = 3.0;
-    let t_1 = sin(globals.time * speed) * 0.5 + 0.5;
-    let t_2 = cos(globals.time * speed);
-
-    let distance_to_center = distance(in.uv, vec2<f32>(0.5)) * 1.4;
-
-    let red = vec3<f32>(0.627955, 0.224863, 0.125846);
-    let green = vec3<f32>(0.86644, -0.233887, 0.179498);
-    let blue = vec3<f32>(0.701674, 0.274566, -0.169156);
-    let white = vec3<f32>(1.0, 0.0, 0.0);
-    let pos = vec3<f32>(in.position[0], in.position[1], in.position[2]);
-    let mixed = mix(pos, mix(green, white, t_2), distance_to_center);
-
-    return vec4<f32>(mixed, 1.0);
-}

src/world.rs

@@ -40,18 +40,27 @@ impl Plugin for WorldPlugin {
         //app.add_systems(Update, asset_loaded.after(load_cubemap_asset));
         //app.add_systems(Update, swap_world_on_ar_toggle);
         app.add_plugins(PhysicsPlugins::default());
-        app.add_plugins(MaterialPlugin::<CustomMaterial>::default());
+        app.add_plugins(MaterialPlugin::<RingMaterial>::default());
         //app.add_plugins(PhysicsDebugPlugin::default());
         app.insert_resource(Gravity(Vec3::splat(0.0)));
     }
 }
 
 #[derive(Asset, TypePath, AsBindGroup, Debug, Clone)]
-pub struct CustomMaterial {}
+pub struct RingMaterial {
+    alpha_mode: AlphaMode,
+    #[uniform(0)]
+    ring_radius: f32,
+    #[uniform(1)]
+    jupiter_radius: f32,
+}
 
-impl Material for CustomMaterial {
+impl Material for RingMaterial {
     fn fragment_shader() -> ShaderRef {
-        "shaders/testshader.wgsl".into()
+        "shaders/jupiters_rings.wgsl".into()
+    }
+    fn alpha_mode(&self) -> AlphaMode {
+        self.alpha_mode
     }
 }
 
@@ -79,7 +88,7 @@ pub fn setup(
     mut commands: Commands,
     mut meshes: ResMut<Assets<Mesh>>,
     mut materials: ResMut<Assets<StandardMaterial>>,
-    mut materials_custom: ResMut<Assets<CustomMaterial>>,
+    mut materials_custom: ResMut<Assets<RingMaterial>>,
     asset_server: Res<AssetServer>,
 ) {
 //    let cubemap_handle = asset_server.load(ASSET_CUBEMAP);
@@ -175,26 +184,43 @@ pub fn setup(
     info!("Generated {starcount} stars");
 
     // Add shaded ring
-    let max = 20;
-    for i in 0..max {
-        let f = i as f32;
-        let maxf = max as f32;
-        let ringmesh = Mesh::from(Cylinder::new(400000.0 + f * 10000.0, 5000.0 - 150.0 * f));
-        let clr = 0.4 + (f/maxf).clamp(0.0,0.6);
-        commands.spawn(MaterialMeshBundle {
-            mesh: meshes.add(ringmesh),
-            transform: Transform::from_xyz(300000.0, 0.0, 500000.0),
-            //material: materials_custom.add(CustomMaterial {}),
-            material: materials.add(StandardMaterial {
-                base_color: Color::rgba(clr, clr, clr, 0.0001),
-                unlit: true,
-                cull_mode: None,
-                alpha_mode: AlphaMode::Blend,
-                ..default()
-            }),
-            ..default()
-        });
-    }
+    let ring_radius = 900000.0;
+    let jupiter_radius = 200000.0;
+    commands.spawn(MaterialMeshBundle {
+        mesh: meshes.add(Mesh::from(Cylinder::new(ring_radius, 1.0))),
+        transform: Transform::from_xyz(300000.0, -4000.0, 500000.0)
+            .with_rotation(Quat::from_rotation_z(PI*0.05))
+        ,
+        //transform: Transform::from_xyz(300000.0, 0.0, 500000.0)),
+        material: materials_custom.add(RingMaterial {
+            alpha_mode: AlphaMode::Blend,
+            ring_radius: ring_radius,
+            jupiter_radius: jupiter_radius,
+        }),
+        ..default()
+    });
+    //let max = 20;
+    //for i in 0..max {
+    //    let f = i as f32;
+    //    let maxf = max as f32;
+    //    let ringmesh = Mesh::from(Cylinder::new(400000.0 + f * 10000.0, 5000.0 - 150.0 * f));
+    //    let clr = 0.4 + (f/maxf).clamp(0.0,0.6);
+    //    commands.spawn(MaterialMeshBundle {
+    //        mesh: meshes.add(ringmesh),
+    //        transform: Transform::from_xyz(300000.0, 0.0, 500000.0),
+    //        material: materials_custom.add(RingMaterial {
+    //            alpha_mode: AlphaMode::Blend,
+    //        }),
+    //        material: materials.add(StandardMaterial {
+    //            base_color: Color::rgba(clr, clr, clr, 0.0001),
+    //            unlit: true,
+    //            cull_mode: None,
+    //            alpha_mode: AlphaMode::Blend,
+    //            ..default()
+    //        }),
+    //        ..default()
+    //    });
+    //}
 
     // Add Light from the Sun
     commands.spawn(DirectionalLightBundle {