Support topologies other than TriangleList (#3349)

# Objective

Fixes #3346

## Solution

I've encoded the topology in the `MeshKey` similar to how MSAA samples are handled.

crates/bevy_pbr/src/render/mesh.rs

@@ -370,12 +370,15 @@ bitflags::bitflags! {
  const VERTEX_TANGENTS = (1 << 0);
  const TRANSPARENT_MAIN_PASS = (1 << 1);
  const MSAA_RESERVED_BITS = MeshPipelineKey::MSAA_MASK_BITS << MeshPipelineKey::MSAA_SHIFT_BITS;
+ const PRIMITIVE_TOPOLOGY_RESERVED_BITS = MeshPipelineKey::PRIMITIVE_TOPOLOGY_MASK_BITS << MeshPipelineKey::PRIMITIVE_TOPOLOGY_SHIFT_BITS;
  }
 }
 
 impl MeshPipelineKey {
  const MSAA_MASK_BITS: u32 = 0b111111;
  const MSAA_SHIFT_BITS: u32 = 32 - 6;
+ const PRIMITIVE_TOPOLOGY_MASK_BITS: u32 = 0b111;
+ const PRIMITIVE_TOPOLOGY_SHIFT_BITS: u32 = Self::MSAA_SHIFT_BITS - 3;
 
  pub fn from_msaa_samples(msaa_samples: u32) -> Self {
  let msaa_bits = ((msaa_samples - 1) & Self::MSAA_MASK_BITS) << Self::MSAA_SHIFT_BITS;
@@ -385,6 +388,26 @@ impl MeshPipelineKey {
  pub fn msaa_samples(&self) -> u32 {
  ((self.bits >> Self::MSAA_SHIFT_BITS) & Self::MSAA_MASK_BITS) + 1
  }
+
+ pub fn from_primitive_topology(primitive_topology: PrimitiveTopology) -> Self {
+ let primitive_topology_bits = ((primitive_topology as u32)
+ & Self::PRIMITIVE_TOPOLOGY_MASK_BITS)
+ << Self::PRIMITIVE_TOPOLOGY_SHIFT_BITS;
+ MeshPipelineKey::from_bits(primitive_topology_bits).unwrap()
+ }
+
+ pub fn primitive_topology(&self) -> PrimitiveTopology {
+ let primitive_topology_bits =
+ (self.bits >> Self::PRIMITIVE_TOPOLOGY_SHIFT_BITS) & Self::PRIMITIVE_TOPOLOGY_MASK_BITS;
+ match primitive_topology_bits {
+ x if x == PrimitiveTopology::PointList as u32 => PrimitiveTopology::PointList,
+ x if x == PrimitiveTopology::LineList as u32 => PrimitiveTopology::LineList,
+ x if x == PrimitiveTopology::LineStrip as u32 => PrimitiveTopology::LineStrip,
+ x if x == PrimitiveTopology::TriangleList as u32 => PrimitiveTopology::TriangleList,
+ x if x == PrimitiveTopology::TriangleStrip as u32 => PrimitiveTopology::TriangleStrip,
+ _ => PrimitiveTopology::default(),
+ }
+ }
 }
 
 impl SpecializedPipeline for MeshPipeline {
@@ -496,7 +519,7 @@ impl SpecializedPipeline for MeshPipeline {
  polygon_mode: PolygonMode::Fill,
  clamp_depth: false,
  conservative: false,
- topology: PrimitiveTopology::TriangleList,
+ topology: key.primitive_topology(),
  strip_index_format: None,
  },
  depth_stencil: Some(DepthStencilState {

crates/bevy_pbr/src/render/mod.rs

@@ -269,6 +269,8 @@ pub fn queue_meshes(
  if mesh.has_tangents {
  pbr_key.mesh_key |= MeshPipelineKey::VERTEX_TANGENTS;
  }
+ pbr_key.mesh_key |=
+ MeshPipelineKey::from_primitive_topology(mesh.primitive_topology);
  }
 
  if let AlphaMode::Blend = material.alpha_mode {

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

@@ -593,6 +593,7 @@ pub struct GpuMesh {
  pub vertex_buffer: Buffer,
  pub index_info: Option<GpuIndexInfo>,
  pub has_tangents: bool,
+ pub primitive_topology: PrimitiveTopology,
 }
 
 /// The index info of a [`GpuMesh`].
@@ -640,6 +641,7 @@ impl RenderAsset for Mesh {
  vertex_buffer,
  index_info,
  has_tangents: mesh.attributes.contains_key(Mesh::ATTRIBUTE_TANGENT),
+ primitive_topology: mesh.primitive_topology(),
  })
  }
 }