WIP cull mode specialization

crates/bevy_pbr/src/material.rs

@@ -65,6 +65,12 @@ pub trait Material: Asset + RenderAsset {
         AlphaMode::Opaque
     }
 
+    /// Returns this material's [`AlphaMode`]. Defaults to [`AlphaMode::Opaque`].
+    #[allow(unused_variables)]
+    fn double_sided(material: &<Self as RenderAsset>::PreparedAsset) -> bool {
+        false
+    }
+
     /// The dynamic uniform indices to set for the given `material`'s [`BindGroup`].
     /// Defaults to an empty array / no dynamic uniform indices.
     #[allow(unused_variables)]
@@ -98,6 +104,11 @@ impl<M: Material> SpecializedMaterial for M {
         <M as Material>::alpha_mode(material)
     }
 
+    #[inline]
+    fn double_sided(material: &<Self as RenderAsset>::PreparedAsset) -> bool {
+        <M as Material>::double_sided(material)
+    }
+
     #[inline]
     fn vertex_shader(asset_server: &AssetServer) -> Option<Handle<Shader>> {
         <M as Material>::vertex_shader(asset_server)
@@ -158,6 +169,12 @@ pub trait SpecializedMaterial: Asset + RenderAsset {
         AlphaMode::Opaque
     }
 
+    /// Returns this material's [`AlphaMode`]. Defaults to [`AlphaMode::Opaque`].
+    #[allow(unused_variables)]
+    fn double_sided(material: &<Self as RenderAsset>::PreparedAsset) -> bool {
+        false
+    }
+
     /// The dynamic uniform indices to set for the given `material`'s [`BindGroup`].
     /// Defaults to an empty array / no dynamic uniform indices.
     #[allow(unused_variables)]
@@ -326,6 +343,9 @@ pub fn queue_material_meshes<M: SpecializedMaterial>(
                     if let AlphaMode::Blend = alpha_mode {
                         mesh_key |= MeshPipelineKey::TRANSPARENT_MAIN_PASS
                     }
+                    if M::double_sided(material) {
+                        mesh_key |= MeshPipelineKey::from_cull_mode(None)
+                    }
 
                     let specialized_key = M::key(material);
                     let pipeline_id = pipelines.specialize(

crates/bevy_pbr/src/pbr_material.rs

@@ -153,6 +153,7 @@ pub struct GpuStandardMaterial {
     pub flags: StandardMaterialFlags,
     pub base_color_texture: Option<Handle<Image>>,
     pub alpha_mode: AlphaMode,
+    pub double_sided: bool,
 }
 
 impl RenderAsset for StandardMaterial {
@@ -320,6 +321,7 @@ impl RenderAsset for StandardMaterial {
             has_normal_map,
             base_color_texture: material.base_color_texture,
             alpha_mode: material.alpha_mode,
+            double_sided: material.double_sided,
         })
     }
 }
@@ -477,4 +479,9 @@ impl SpecializedMaterial for StandardMaterial {
     fn alpha_mode(render_asset: &<Self as RenderAsset>::PreparedAsset) -> AlphaMode {
         render_asset.alpha_mode
     }
+
+    #[inline]
+    fn double_sided(render_asset: &<Self as RenderAsset>::PreparedAsset) -> bool {
+        render_asset.double_sided
+    }
 }

crates/bevy_pbr/src/render/mesh.rs

@@ -372,6 +372,7 @@ bitflags::bitflags! {
         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;
+        const CULL_MODE_RESERVED_BITS = MeshPipelineKey::CULL_MODE_MASK_BITS << MeshPipelineKey::CULL_MODE_SHIFT_BITS;
     }
 }
 
@@ -380,6 +381,8 @@ impl MeshPipelineKey {
     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;
+    const CULL_MODE_MASK_BITS: u32 = 0b11;
+    const CULL_MODE_SHIFT_BITS: u32 = Self::PRIMITIVE_TOPOLOGY_SHIFT_BITS - 2;
 
     pub fn from_msaa_samples(msaa_samples: u32) -> Self {
         let msaa_bits = ((msaa_samples - 1) & Self::MSAA_MASK_BITS) << Self::MSAA_SHIFT_BITS;
@@ -409,6 +412,26 @@ impl MeshPipelineKey {
             _ => PrimitiveTopology::default(),
         }
     }
+
+    pub fn from_cull_mode(cull_mode: Option<Face>) -> Self {
+        let cull_mode = match cull_mode {
+            Some(Face::Back) => 0,
+            Some(Face::Front) => 1,
+            None => 2,
+        };
+        let cull_mode_bits = (cull_mode & Self::CULL_MODE_MASK_BITS) << Self::CULL_MODE_SHIFT_BITS;
+        MeshPipelineKey::from_bits(cull_mode_bits).unwrap()
+    }
+
+    pub fn cull_mode(&self) -> Option<Face> {
+        let cull_mode_bits = (self.bits >> Self::CULL_MODE_SHIFT_BITS) & Self::CULL_MODE_MASK_BITS;
+        match cull_mode_bits {
+            0 => Some(Face::Back),
+            1 => Some(Face::Front),
+            2 => None,
+            _ => Some(Face::Back),
+        }
+    }
 }
 
 impl SpecializedPipeline for MeshPipeline {
@@ -519,7 +542,7 @@ impl SpecializedPipeline for MeshPipeline {
             layout: Some(vec![self.view_layout.clone(), self.mesh_layout.clone()]),
             primitive: PrimitiveState {
                 front_face: FrontFace::Ccw,
-                cull_mode: Some(Face::Back),
+                cull_mode: key.cull_mode(),
                 unclipped_depth: false,
                 polygon_mode: PolygonMode::Fill,
                 conservative: false,