Primitive 3d custom tangents

crates/bevy_mesh/src/mesh.rs

@@ -237,6 +237,35 @@ impl Mesh {
             .insert(attribute.id, MeshAttributeData { attribute, values });
     }
 
+    /// Sets the data for a vertex attribute (position, normal, etc.) if not empty.
+    /// The name will often be one of the associated constants such
+    /// as [`Mesh::ATTRIBUTE_POSITION`].
+    ///
+    /// `Aabb` of entities with modified mesh are not updated automatically.
+    ///
+    /// # Panics
+    /// Panics when the format of the values does not match the attribute's format.
+    #[inline]
+    pub fn insert_attribute_if_not_empty(
+        &mut self,
+        attribute: MeshVertexAttribute,
+        values: impl Into<VertexAttributeValues>,
+    ) {
+        let values = values.into();
+        if !values.is_empty() {
+            let values_format = VertexFormat::from(&values);
+            if values_format != attribute.format {
+                panic!(
+                "Failed to insert attribute. Invalid attribute format for {}. Given format is {values_format:?} but expected {:?}",
+                attribute.name, attribute.format
+            );
+            }
+
+            self.attributes
+                .insert(attribute.id, MeshAttributeData { attribute, values });
+        }
+    }
+
     /// Consumes the mesh and returns a mesh with data set for a vertex attribute (position, normal, etc.).
     /// The name will often be one of the associated constants such as [`Mesh::ATTRIBUTE_POSITION`].
     ///
@@ -257,6 +286,27 @@ impl Mesh {
         self
     }
 
+    /// Consumes the mesh and returns a mesh with data set for a vertex attribute (position, normal, etc.)
+    /// if it is not empty.
+    /// The name will often be one of the associated constants such as [`Mesh::ATTRIBUTE_POSITION`].
+    ///
+    /// (Alternatively, you can use [`Mesh::insert_attribute`] to mutate an existing mesh in-place)
+    ///
+    /// `Aabb` of entities with modified mesh are not updated automatically.
+    ///
+    /// # Panics
+    /// Panics when the format of the values does not match the attribute's format.
+    #[must_use]
+    #[inline]
+    pub fn with_inserted_attribute_if_not_empty(
+        mut self,
+        attribute: MeshVertexAttribute,
+        values: impl Into<VertexAttributeValues>,
+    ) -> Self {
+        self.insert_attribute_if_not_empty(attribute, values);
+        self
+    }
+
     /// Removes the data for a vertex attribute
     pub fn remove_attribute(
         &mut self,

crates/bevy_mesh/src/primitives/dim3/mod.rs

@@ -19,3 +19,13 @@ pub use sphere::*;
 pub use tetrahedron::*;
 pub use torus::*;
 pub use triangle3d::*;
+
+use bevy_math::{Dir3, Vec3};
+
+fn calculate_tangents_around_axis(normals: &[[f32; 3]], tangent_axis: &Dir3) -> Vec<[f32; 4]> {
+    normals
+        .iter()
+        .map(|normal| Vec3::from_array(*normal))
+        .map(|normal| tangent_axis.cross(normal).extend(1.).to_array())
+        .collect()
+}

crates/bevy_mesh/src/primitives/dim3/sphere.rs

@@ -1,6 +1,6 @@
 use crate::{Indices, Mesh, MeshBuilder, Meshable, PrimitiveTopology};
 use bevy_asset::RenderAssetUsages;
-use bevy_math::{ops, primitives::Sphere};
+use bevy_math::{ops, primitives::Sphere, Dir3};
 use bevy_reflect::prelude::*;
 use core::f32::consts::PI;
 use hexasphere::shapes::IcoSphere;
@@ -55,6 +55,8 @@ pub struct SphereMeshBuilder {
     pub sphere: Sphere,
     /// The type of sphere mesh that will be built.
     pub kind: SphereKind,
+    /// Axis around which the tangents will be calculated
+    pub tangent_axis: Option<Dir3>,
 }
 
 impl SphereMeshBuilder {
@@ -64,6 +66,7 @@ impl SphereMeshBuilder {
         Self {
             sphere: Sphere { radius },
             kind,
+            tangent_axis: None,
         }
     }
 
@@ -74,6 +77,13 @@ impl SphereMeshBuilder {
         self
     }
 
+    /// Sets the tangent axis that will be used to calculate mesh tangents.
+    #[inline]
+    pub const fn with_tangent_axis(mut self, axis: Dir3) -> Self {
+        self.tangent_axis.replace(axis);
+        self
+    }
+
     /// Creates an icosphere mesh with the given number of subdivisions.
     ///
     /// The number of faces quadruples with each subdivision.
@@ -151,14 +161,21 @@ impl SphereMeshBuilder {
 
         let indices = Indices::U32(indices);
 
+        let tangent = if let Some(tangent_axis) = self.tangent_axis {
+            super::calculate_tangents_around_axis(normals.as_slice(), &tangent_axis)
+        } else {
+            vec![]
+        };
+
         Ok(Mesh::new(
             PrimitiveTopology::TriangleList,
             RenderAssetUsages::default(),
         )
         .with_inserted_indices(indices)
         .with_inserted_attribute(Mesh::ATTRIBUTE_POSITION, points)
         .with_inserted_attribute(Mesh::ATTRIBUTE_NORMAL, normals)
-        .with_inserted_attribute(Mesh::ATTRIBUTE_UV_0, uvs))
+        .with_inserted_attribute(Mesh::ATTRIBUTE_UV_0, uvs)
+        .with_inserted_attribute_if_not_empty(Mesh::ATTRIBUTE_TANGENT, tangent))
     }
 
     /// Creates a UV sphere [`Mesh`] with the given number of
@@ -220,6 +237,12 @@ impl SphereMeshBuilder {
             }
         }
 
+        let tangents = if let Some(tangent_axis) = self.tangent_axis {
+            super::calculate_tangents_around_axis(normals.as_slice(), &tangent_axis)
+        } else {
+            vec![]
+        };
+
         Mesh::new(
             PrimitiveTopology::TriangleList,
             RenderAssetUsages::default(),
@@ -228,6 +251,7 @@ impl SphereMeshBuilder {
         .with_inserted_attribute(Mesh::ATTRIBUTE_POSITION, vertices)
         .with_inserted_attribute(Mesh::ATTRIBUTE_NORMAL, normals)
         .with_inserted_attribute(Mesh::ATTRIBUTE_UV_0, uvs)
+        .with_inserted_attribute_if_not_empty(Mesh::ATTRIBUTE_TANGENT, tangents)
     }
 }