1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273
use bevy_math::{primitives::Cone, Vec3};
use wgpu::PrimitiveTopology;
use crate::{
mesh::{Indices, Mesh, MeshBuilder, Meshable},
render_asset::RenderAssetUsages,
};
/// Anchoring options for [`ConeMeshBuilder`]
#[derive(Debug, Copy, Clone, Default)]
pub enum ConeAnchor {
#[default]
/// Midpoint between the tip of the cone and the center of its base.
MidPoint,
/// The Tip of the triangle
Tip,
/// The center of the base circle
Base,
}
/// A builder used for creating a [`Mesh`] with a [`Cone`] shape.
#[derive(Clone, Copy, Debug)]
pub struct ConeMeshBuilder {
/// The [`Cone`] shape.
pub cone: Cone,
/// The number of vertices used for the base of the cone.
///
/// The default is `32`.
pub resolution: u32,
/// The anchor point for the cone mesh, defaults to the midpoint between
/// the tip of the cone and the center of its base
pub anchor: ConeAnchor,
}
impl Default for ConeMeshBuilder {
fn default() -> Self {
Self {
cone: Cone::default(),
resolution: 32,
anchor: ConeAnchor::default(),
}
}
}
impl ConeMeshBuilder {
/// Creates a new [`ConeMeshBuilder`] from a given radius, height,
/// and number of vertices used for the base of the cone.
#[inline]
pub const fn new(radius: f32, height: f32, resolution: u32) -> Self {
Self {
cone: Cone { radius, height },
resolution,
anchor: ConeAnchor::MidPoint,
}
}
/// Sets the number of vertices used for the base of the cone.
#[inline]
pub const fn resolution(mut self, resolution: u32) -> Self {
self.resolution = resolution;
self
}
/// Sets a custom anchor point for the mesh
#[inline]
pub const fn anchor(mut self, anchor: ConeAnchor) -> Self {
self.anchor = anchor;
self
}
}
impl MeshBuilder for ConeMeshBuilder {
fn build(&self) -> Mesh {
let half_height = self.cone.height / 2.0;
// `resolution` vertices for the base, `resolution` vertices for the bottom of the lateral surface,
// and one vertex for the tip.
let num_vertices = self.resolution as usize * 2 + 1;
let num_indices = self.resolution as usize * 6 - 6;
let mut positions = Vec::with_capacity(num_vertices);
let mut normals = Vec::with_capacity(num_vertices);
let mut uvs = Vec::with_capacity(num_vertices);
let mut indices = Vec::with_capacity(num_indices);
// Tip
positions.push([0.0, half_height, 0.0]);
// The tip doesn't have a singular normal that works correctly.
// We use an invalid normal here so that it becomes NaN in the fragment shader
// and doesn't affect the overall shading. This might seem hacky, but it's one of
// the only ways to get perfectly smooth cones without creases or other shading artefacts.
//
// Note that this requires that normals are not normalized in the vertex shader,
// as that would make the entire triangle invalid and make the cone appear as black.
normals.push([0.0, 0.0, 0.0]);
// The UVs of the cone are in polar coordinates, so it's like projecting a circle texture from above.
// The center of the texture is at the center of the lateral surface, at the tip of the cone.
uvs.push([0.5, 0.5]);
// Now we build the lateral surface, the side of the cone.
// The vertex normals will be perpendicular to the surface.
//
// Here we get the slope of a normal and use it for computing
// the multiplicative inverse of the length of a vector in the direction
// of the normal. This allows us to normalize vertex normals efficiently.
let normal_slope = self.cone.radius / self.cone.height;
// Equivalent to Vec2::new(1.0, slope).length().recip()
let normalization_factor = (1.0 + normal_slope * normal_slope).sqrt().recip();
// How much the angle changes at each step
let step_theta = std::f32::consts::TAU / self.resolution as f32;
// Add vertices for the bottom of the lateral surface.
for segment in 0..self.resolution {
let theta = segment as f32 * step_theta;
let (sin, cos) = theta.sin_cos();
// The vertex normal perpendicular to the side
let normal = Vec3::new(cos, normal_slope, sin) * normalization_factor;
positions.push([self.cone.radius * cos, -half_height, self.cone.radius * sin]);
normals.push(normal.to_array());
uvs.push([0.5 + cos * 0.5, 0.5 + sin * 0.5]);
}
// Add indices for the lateral surface. Each triangle is formed by the tip
// and two vertices at the base.
for j in 1..self.resolution {
indices.extend_from_slice(&[0, j + 1, j]);
}
// Close the surface with a triangle between the tip, first base vertex, and last base vertex.
indices.extend_from_slice(&[0, 1, self.resolution]);
// Now we build the actual base of the cone.
let index_offset = positions.len() as u32;
// Add base vertices.
for i in 0..self.resolution {
let theta = i as f32 * step_theta;
let (sin, cos) = theta.sin_cos();
positions.push([cos * self.cone.radius, -half_height, sin * self.cone.radius]);
normals.push([0.0, -1.0, 0.0]);
uvs.push([0.5 * (cos + 1.0), 1.0 - 0.5 * (sin + 1.0)]);
}
// Add base indices.
for i in 1..(self.resolution - 1) {
indices.extend_from_slice(&[index_offset, index_offset + i, index_offset + i + 1]);
}
// Offset the vertex positions Y axis to match the anchor
match self.anchor {
ConeAnchor::Tip => positions.iter_mut().for_each(|p| p[1] -= half_height),
ConeAnchor::Base => positions.iter_mut().for_each(|p| p[1] += half_height),
ConeAnchor::MidPoint => (),
};
Mesh::new(
PrimitiveTopology::TriangleList,
RenderAssetUsages::default(),
)
.with_inserted_indices(Indices::U32(indices))
.with_inserted_attribute(Mesh::ATTRIBUTE_POSITION, positions)
.with_inserted_attribute(Mesh::ATTRIBUTE_NORMAL, normals)
.with_inserted_attribute(Mesh::ATTRIBUTE_UV_0, uvs)
}
}
impl Meshable for Cone {
type Output = ConeMeshBuilder;
fn mesh(&self) -> Self::Output {
ConeMeshBuilder {
cone: *self,
..Default::default()
}
}
}
impl From<Cone> for Mesh {
fn from(cone: Cone) -> Self {
cone.mesh().build()
}
}
#[cfg(test)]
mod tests {
use bevy_math::{primitives::Cone, Vec2};
use crate::mesh::{primitives::MeshBuilder, Mesh, Meshable, VertexAttributeValues};
/// Rounds floats to handle floating point error in tests.
fn round_floats<const N: usize>(points: &mut [[f32; N]]) {
for point in points.iter_mut() {
for coord in point.iter_mut() {
let round = (*coord * 100.0).round() / 100.0;
if (*coord - round).abs() < 0.00001 {
*coord = round;
}
}
}
}
#[test]
fn cone_mesh() {
let mut mesh = Cone {
radius: 0.5,
height: 1.0,
}
.mesh()
.resolution(4)
.build();
let Some(VertexAttributeValues::Float32x3(mut positions)) =
mesh.remove_attribute(Mesh::ATTRIBUTE_POSITION)
else {
panic!("Expected positions f32x3");
};
let Some(VertexAttributeValues::Float32x3(mut normals)) =
mesh.remove_attribute(Mesh::ATTRIBUTE_NORMAL)
else {
panic!("Expected normals f32x3");
};
round_floats(&mut positions);
round_floats(&mut normals);
// Vertex positions
assert_eq!(
[
// Tip
[0.0, 0.5, 0.0],
// Lateral surface
[0.5, -0.5, 0.0],
[0.0, -0.5, 0.5],
[-0.5, -0.5, 0.0],
[0.0, -0.5, -0.5],
// Base
[0.5, -0.5, 0.0],
[0.0, -0.5, 0.5],
[-0.5, -0.5, 0.0],
[0.0, -0.5, -0.5],
],
&positions[..]
);
// Vertex normals
let [x, y] = Vec2::new(0.5, -1.0).perp().normalize().to_array();
assert_eq!(
&[
// Tip
[0.0, 0.0, 0.0],
// Lateral surface
[x, y, 0.0],
[0.0, y, x],
[-x, y, 0.0],
[0.0, y, -x],
// Base
[0.0, -1.0, 0.0],
[0.0, -1.0, 0.0],
[0.0, -1.0, 0.0],
[0.0, -1.0, 0.0],
],
&normals[..]
);
}
}