bevy_render/mesh/primitives/extrusion.rs
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use bevy_math::{
primitives::{Annulus, Capsule2d, Circle, Ellipse, Extrusion, Primitive2d},
Vec2, Vec3,
};
use crate::mesh::{Indices, Mesh, VertexAttributeValues};
use super::{MeshBuilder, Meshable};
/// A type representing a segment of the perimeter of an extrudable mesh.
pub enum PerimeterSegment {
/// This segment of the perimeter will be shaded smooth.
///
/// This has the effect of rendering the segment's faces with softened edges, so it is appropriate for curved shapes.
///
/// The normals for the vertices that are part of this segment will be calculated based on the positions of their neighbours.
/// Each normal is interpolated between the normals of the two line segments connecting it with its neighbours.
/// Closer vertices have a stronger effect on the normal than more distant ones.
///
/// Since the vertices corresponding to the first and last indices do not have two neighbouring vertices, their normals must be provided manually.
Smooth {
/// The normal of the first vertex.
first_normal: Vec2,
/// The normal of the last vertex.
last_normal: Vec2,
/// A list of indices representing this segment of the perimeter of the mesh.
///
/// The indices must be ordered such that the *outside* of the mesh is to the right
/// when walking along the vertices of the mesh in the order provided by the indices.
///
/// For geometry to be rendered, you must provide at least two indices.
indices: Vec<u32>,
},
/// This segment of the perimeter will be shaded flat.
///
/// This has the effect of rendering the segment's faces with hard edges.
Flat {
/// A list of indices representing this segment of the perimeter of the mesh.
///
/// The indices must be ordered such that the *outside* of the mesh is to the right
/// when walking along the vertices of the mesh in the order provided by indices.
///
/// For geometry to be rendered, you must provide at least two indices.
indices: Vec<u32>,
},
}
impl PerimeterSegment {
/// Returns the amount of vertices each 'layer' of the extrusion should include for this perimeter segment.
///
/// A layer is the set of vertices sharing a common Z value or depth.
fn vertices_per_layer(&self) -> usize {
match self {
PerimeterSegment::Smooth { indices, .. } => indices.len(),
PerimeterSegment::Flat { indices } => 2 * (indices.len() - 1),
}
}
/// Returns the amount of indices each 'segment' of the extrusion should include for this perimeter segment.
///
/// A segment is the set of faces on the mantel of the extrusion between two layers of vertices.
fn indices_per_segment(&self) -> usize {
match self {
PerimeterSegment::Smooth { indices, .. } | PerimeterSegment::Flat { indices } => {
6 * (indices.len() - 1)
}
}
}
}
/// A trait for required for implementing `Meshable` for `Extrusion<T>`.
///
/// ## Warning
///
/// By implementing this trait you guarantee that the `primitive_topology` of the mesh returned by
/// this builder is [`PrimitiveTopology::TriangleList`](wgpu::PrimitiveTopology::TriangleList)
/// and that your mesh has a [`Mesh::ATTRIBUTE_POSITION`] attribute.
pub trait Extrudable: MeshBuilder {
/// A list of the indices each representing a part of the perimeter of the mesh.
fn perimeter(&self) -> Vec<PerimeterSegment>;
}
impl<P> Meshable for Extrusion<P>
where
P: Primitive2d + Meshable,
P::Output: Extrudable,
{
type Output = ExtrusionBuilder<P>;
fn mesh(&self) -> Self::Output {
ExtrusionBuilder {
base_builder: self.base_shape.mesh(),
half_depth: self.half_depth,
segments: 1,
}
}
}
/// A builder used for creating a [`Mesh`] with an [`Extrusion`] shape.
pub struct ExtrusionBuilder<P>
where
P: Primitive2d + Meshable,
P::Output: Extrudable,
{
pub base_builder: P::Output,
pub half_depth: f32,
pub segments: usize,
}
impl<P> ExtrusionBuilder<P>
where
P: Primitive2d + Meshable,
P::Output: Extrudable,
{
/// Create a new `ExtrusionBuilder<P>` from a given `base_shape` and the full `depth` of the extrusion.
pub fn new(base_shape: &P, depth: f32) -> Self {
Self {
base_builder: base_shape.mesh(),
half_depth: depth / 2.,
segments: 1,
}
}
/// Sets the number of segments along the depth of the extrusion.
/// Must be greater than `0` for the geometry of the mantel to be generated.
pub fn segments(mut self, segments: usize) -> Self {
self.segments = segments;
self
}
}
impl ExtrusionBuilder<Circle> {
/// Sets the number of vertices used for the circle mesh at each end of the extrusion.
pub fn resolution(mut self, resolution: usize) -> Self {
self.base_builder.resolution = resolution;
self
}
}
impl ExtrusionBuilder<Ellipse> {
/// Sets the number of vertices used for the ellipse mesh at each end of the extrusion.
pub fn resolution(mut self, resolution: usize) -> Self {
self.base_builder.resolution = resolution;
self
}
}
impl ExtrusionBuilder<Annulus> {
/// Sets the number of vertices used in constructing the concentric circles of the annulus mesh at each end of the extrusion.
pub fn resolution(mut self, resolution: usize) -> Self {
self.base_builder.resolution = resolution;
self
}
}
impl ExtrusionBuilder<Capsule2d> {
/// Sets the number of vertices used for each hemicircle at the ends of the extrusion.
pub fn resolution(mut self, resolution: usize) -> Self {
self.base_builder.resolution = resolution;
self
}
}
impl<P> MeshBuilder for ExtrusionBuilder<P>
where
P: Primitive2d + Meshable,
P::Output: Extrudable,
{
fn build(&self) -> Mesh {
// Create and move the base mesh to the front
let mut front_face =
self.base_builder
.build()
.translated_by(Vec3::new(0., 0., self.half_depth));
// Move the uvs of the front face to be between (0., 0.) and (0.5, 0.5)
if let Some(VertexAttributeValues::Float32x2(uvs)) =
front_face.attribute_mut(Mesh::ATTRIBUTE_UV_0)
{
for uv in uvs {
*uv = uv.map(|coord| coord * 0.5);
}
}
let back_face = {
let topology = front_face.primitive_topology();
// Flip the normals, etc. and move mesh to the back
let mut back_face = front_face.clone().scaled_by(Vec3::new(1., 1., -1.));
// Move the uvs of the back face to be between (0.5, 0.) and (1., 0.5)
if let Some(VertexAttributeValues::Float32x2(uvs)) =
back_face.attribute_mut(Mesh::ATTRIBUTE_UV_0)
{
for uv in uvs {
*uv = [uv[0] + 0.5, uv[1]];
}
}
// By swapping the first and second indices of each triangle we invert the winding order thus making the mesh visible from the other side
if let Some(indices) = back_face.indices_mut() {
match topology {
wgpu::PrimitiveTopology::TriangleList => match indices {
Indices::U16(indices) => {
indices.chunks_exact_mut(3).for_each(|arr| arr.swap(1, 0));
}
Indices::U32(indices) => {
indices.chunks_exact_mut(3).for_each(|arr| arr.swap(1, 0));
}
},
_ => {
panic!("Meshes used with Extrusions must have a primitive topology of `PrimitiveTopology::TriangleList`");
}
};
}
back_face
};
// An extrusion of depth 0 does not need a mantel
if self.half_depth == 0. {
front_face.merge(&back_face);
return front_face;
}
let mantel = {
let Some(VertexAttributeValues::Float32x3(cap_verts)) =
front_face.attribute(Mesh::ATTRIBUTE_POSITION)
else {
panic!("The base mesh did not have vertex positions");
};
debug_assert!(self.segments > 0);
let layers = self.segments + 1;
let layer_depth_delta = self.half_depth * 2.0 / self.segments as f32;
let perimeter = self.base_builder.perimeter();
let (vert_count, index_count) =
perimeter
.iter()
.fold((0, 0), |(verts, indices), perimeter| {
(
verts + layers * perimeter.vertices_per_layer(),
indices + self.segments * perimeter.indices_per_segment(),
)
});
let mut positions = Vec::with_capacity(vert_count);
let mut normals = Vec::with_capacity(vert_count);
let mut indices = Vec::with_capacity(index_count);
let mut uvs = Vec::with_capacity(vert_count);
// Compute the amount of horizontal space allocated to each segment of the perimeter.
let uv_segment_delta = 1. / perimeter.len() as f32;
for (i, segment) in perimeter.into_iter().enumerate() {
// The start of the x range of the area of the current perimeter-segment.
let uv_start = i as f32 * uv_segment_delta;
match segment {
PerimeterSegment::Flat {
indices: segment_indices,
} => {
let uv_delta = uv_segment_delta / (segment_indices.len() - 1) as f32;
for i in 0..(segment_indices.len() - 1) {
let uv_x = uv_start + uv_delta * i as f32;
// Get the positions for the current and the next index.
let a = cap_verts[segment_indices[i] as usize];
let b = cap_verts[segment_indices[i + 1] as usize];
// Get the index of the next vertex added to the mantel.
let index = positions.len() as u32;
// Push the positions of the two indices and their equivalent points on each layer.
for i in 0..layers {
let i = i as f32;
let z = a[2] - layer_depth_delta * i;
positions.push([a[0], a[1], z]);
positions.push([b[0], b[1], z]);
// UVs for the mantel are between (0, 0.5) and (1, 1).
let uv_y = 0.5 + 0.5 * i / self.segments as f32;
uvs.push([uv_x, uv_y]);
uvs.push([uv_x + uv_delta, uv_y]);
}
// The normal is calculated to be the normal of the line segment connecting a and b.
let n = Vec3::from_array([b[1] - a[1], a[0] - b[0], 0.])
.normalize_or_zero()
.to_array();
normals.extend_from_slice(&vec![n; 2 * layers]);
// Add the indices for the vertices created above to the mesh.
for i in 0..self.segments as u32 {
let base_index = index + 2 * i;
indices.extend_from_slice(&[
base_index,
base_index + 2,
base_index + 1,
base_index + 1,
base_index + 2,
base_index + 3,
]);
}
}
}
PerimeterSegment::Smooth {
first_normal,
last_normal,
indices: segment_indices,
} => {
let uv_delta = uv_segment_delta / (segment_indices.len() - 1) as f32;
// Since the indices for this segment will be added after its vertices have been added,
// we need to store the index of the first vertex that is part of this segment.
let base_index = positions.len() as u32;
// If there is a first vertex, we need to add it and its counterparts on each layer.
// The normal is provided by `segment.first_normal`.
if let Some(i) = segment_indices.first() {
let p = cap_verts[*i as usize];
for i in 0..layers {
let i = i as f32;
let z = p[2] - layer_depth_delta * i;
positions.push([p[0], p[1], z]);
let uv_y = 0.5 + 0.5 * i / self.segments as f32;
uvs.push([uv_start, uv_y]);
}
normals.extend_from_slice(&vec![
first_normal.extend(0.).to_array();
layers
]);
}
// For all points inbetween the first and last vertices, we can automatically compute the normals.
for i in 1..(segment_indices.len() - 1) {
let uv_x = uv_start + uv_delta * i as f32;
// Get the positions for the last, current and the next index.
let a = cap_verts[segment_indices[i - 1] as usize];
let b = cap_verts[segment_indices[i] as usize];
let c = cap_verts[segment_indices[i + 1] as usize];
// Add the current vertex and its counterparts on each layer.
for i in 0..layers {
let i = i as f32;
let z = b[2] - layer_depth_delta * i;
positions.push([b[0], b[1], z]);
let uv_y = 0.5 + 0.5 * i / self.segments as f32;
uvs.push([uv_x, uv_y]);
}
// The normal for the current vertices can be calculated based on the two neighbouring vertices.
// The normal is interpolated between the normals of the two line segments connecting the current vertex with its neighbours.
// Closer vertices have a stronger effect on the normal than more distant ones.
let n = {
let ab = Vec2::from_slice(&b) - Vec2::from_slice(&a);
let bc = Vec2::from_slice(&c) - Vec2::from_slice(&b);
let n = ab.normalize_or_zero() + bc.normalize_or_zero();
Vec2::new(n.y, -n.x)
.normalize_or_zero()
.extend(0.)
.to_array()
};
normals.extend_from_slice(&vec![n; layers]);
}
// If there is a last vertex, we need to add it and its counterparts on each layer.
// The normal is provided by `segment.last_normal`.
if let Some(i) = segment_indices.last() {
let p = cap_verts[*i as usize];
for i in 0..layers {
let i = i as f32;
let z = p[2] - layer_depth_delta * i;
positions.push([p[0], p[1], z]);
let uv_y = 0.5 + 0.5 * i / self.segments as f32;
uvs.push([uv_start + uv_segment_delta, uv_y]);
}
normals.extend_from_slice(&vec![
last_normal.extend(0.).to_array();
layers
]);
}
let columns = segment_indices.len() as u32;
let segments = self.segments as u32;
let layers = segments + 1;
for s in 0..segments {
for column in 0..(columns - 1) {
let index = base_index + s + column * layers;
indices.extend_from_slice(&[
index,
index + 1,
index + layers,
index + layers,
index + 1,
index + layers + 1,
]);
}
}
}
}
}
Mesh::new(
wgpu::PrimitiveTopology::TriangleList,
front_face.asset_usage,
)
.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)
};
front_face.merge(&back_face);
front_face.merge(&mantel);
front_face
}
}
impl<P> From<Extrusion<P>> for Mesh
where
P: Primitive2d + Meshable,
P::Output: Extrudable,
{
fn from(value: Extrusion<P>) -> Self {
value.mesh().build()
}
}