Add meshing for Cone

crates/bevy_math/src/primitives/dim3.rs

@@ -520,6 +520,16 @@ pub struct Cone {
 }
 impl Primitive3d for Cone {}
 
+impl Default for Cone {
+    /// Returns the default [`Cone`] with a base radius of `0.5` and a height of `1.0`.
+    fn default() -> Self {
+        Self {
+            radius: 0.5,
+            height: 1.0,
+        }
+    }
+}
+
 impl Cone {
     /// Get the base of the cone as a [`Circle`]
     #[inline(always)]

crates/bevy_render/src/mesh/primitives/dim3/cone.rs

@@ -0,0 +1,247 @@
+use bevy_math::{primitives::Cone, Vec3};
+use wgpu::PrimitiveTopology;
+
+use crate::{
+    mesh::{Indices, Mesh, Meshable},
+    render_asset::RenderAssetUsages,
+};
+
+/// 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,
+}
+
+impl Default for ConeMeshBuilder {
+    fn default() -> Self {
+        Self {
+            cone: Cone::default(),
+            resolution: 32,
+        }
+    }
+}
+
+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,
+        }
+    }
+
+    /// 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
+    }
+
+    /// Builds a [`Mesh`] based on the configuration in `self`.
+    pub 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]);
+        }
+
+        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()
+    }
+}
+
+impl From<ConeMeshBuilder> for Mesh {
+    fn from(cone: ConeMeshBuilder) -> Self {
+        cone.build()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use bevy_math::{primitives::Cone, Vec2};
+
+    use crate::mesh::{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[..]
+        );
+    }
+}

crates/bevy_render/src/mesh/primitives/dim3/mod.rs

@@ -1,4 +1,5 @@
 mod capsule;
+mod cone;
 mod cuboid;
 mod cylinder;
 mod plane;
@@ -7,6 +8,7 @@ mod torus;
 pub(crate) mod triangle3d;
 
 pub use capsule::*;
+pub use cone::*;
 pub use cylinder::*;
 pub use plane::*;
 pub use sphere::*;

examples/3d/3d_shapes.rs

@@ -42,6 +42,7 @@ fn setup(
         meshes.add(Capsule3d::default()),
         meshes.add(Torus::default()),
         meshes.add(Cylinder::default()),
+        meshes.add(Cone::default()),
         meshes.add(Sphere::default().mesh().ico(5).unwrap()),
         meshes.add(Sphere::default().mesh().uv(32, 18)),
     ];