Manually construct Mesh from IcoSphere to do noise displacement.

Cargo.lock

@@ -1066,8 +1066,10 @@ dependencies = [
  "bevy",
  "bevy_polyline",
  "bevy_rapier3d",
+ "hexasphere",
  "noise",
  "rand 0.8.5",
+ "wgpu",
 ]
 
 [[package]]

Cargo.toml

@@ -7,6 +7,8 @@ edition = "2021"
 rand = "0.8"
 bevy_polyline = "0.1"
 noise = { git = "https://github.com/Razaekel/noise-rs" }
+hexasphere = "6.0.0"
+wgpu = "0.12.0"
 
 [dependencies.bevy]
 version = "0.6"

src/geometry.rs

@@ -1,4 +1,10 @@
-use bevy::prelude::*;
+use bevy::{
+    prelude::{shape::Icosphere, *},
+    render::mesh::Indices,
+};
+use hexasphere::shapes::IcoSphere;
+use noise::{HybridMulti, NoiseFn, Perlin};
+use wgpu::PrimitiveTopology;
 
 use crate::Label;
 
@@ -17,13 +23,18 @@ fn spawn_giant_sphere(
     mut materials: ResMut<Assets<StandardMaterial>>,
 ) {
     let mut color = Color::DARK_GRAY;
-    color.set_a(0.8);
+    color.set_a(0.92);
+
+    let isphere = shape::Icosphere {
+        radius: PLANET_RADIUS,
+        subdivisions: 26,
+    };
+
+    let pmesh = gen_planet(isphere);
+
     commands
         .spawn_bundle(PbrBundle {
-            mesh: meshes.add(Mesh::from(shape::Icosphere {
-                radius: PLANET_RADIUS,
-                subdivisions: 24,
-            })),
+            mesh: meshes.add(pmesh),
             material: materials.add(StandardMaterial {
                 base_color: color,
                 metallic: 0.65,
@@ -60,3 +71,60 @@ impl Plugin for CyberGeomPlugin {
             .add_startup_system(spawn_cyberbike.label(Label::Geometry));
     }
 }
+
+//---------------------------------------------------------------------
+// utils
+//---------------------------------------------------------------------
+
+fn gen_planet(sphere: Icosphere) -> Mesh {
+    // straight-up stolen from Bevy's impl of Mesh from Icosphere, so I can do the
+    // displacement before normals are calculated.
+    let generated = IcoSphere::new(sphere.subdivisions, |point| {
+        let inclination = point.y.acos();
+        let azimuth = point.z.atan2(point.x);
+
+        let norm_inclination = inclination / std::f32::consts::PI;
+        let norm_azimuth = 0.5 - (azimuth / std::f32::consts::TAU);
+
+        [norm_azimuth, norm_inclination]
+    });
+
+    // TODO: use displaced points for normals by replacing raw_points with
+    // noise-displaced points.
+    let noise = HybridMulti::<Perlin>::default();
+    let raw_points = generated.raw_points();
+
+    let points = raw_points
+        .iter()
+        .map(|&p| {
+            let pt = p * sphere.radius;
+            let disp = noise.get(pt.as_dvec3().into()) as f32;
+            let disp = p * disp * 20.0;
+            let pt = pt + disp;
+            pt.into()
+        })
+        .collect::<Vec<[f32; 3]>>();
+
+    let normals = raw_points
+        .iter()
+        .copied()
+        .map(Into::into)
+        .collect::<Vec<[f32; 3]>>();
+
+    let uvs = generated.raw_data().to_owned();
+
+    let mut indices = Vec::with_capacity(generated.indices_per_main_triangle() * 20);
+
+    for i in 0..20 {
+        generated.get_indices(i, &mut indices);
+    }
+
+    let indices = Indices::U32(indices);
+
+    let mut mesh = Mesh::new(PrimitiveTopology::TriangleList);
+    mesh.set_indices(Some(indices));
+    mesh.set_attribute(Mesh::ATTRIBUTE_POSITION, points);
+    mesh.set_attribute(Mesh::ATTRIBUTE_NORMAL, normals);
+    mesh.set_attribute(Mesh::ATTRIBUTE_UV_0, uvs);
+    mesh
+}