From d32d7dacd10f621e68ad74bd4a38849d8404ab78 Mon Sep 17 00:00:00 2001
From: VictorElHajj <hajjvictor@live.se>
Date: Mon, 22 Jun 2026 19:31:14 +0200
Subject: [PATCH] Add prepass_reads_material flag in material that sets
 PREPASS_READS_MATERIAL

---
 crates/bevy_material/src/lib.rs          |  2 ++
 crates/bevy_pbr/src/extended_material.rs |  9 +++++++++
 crates/bevy_pbr/src/material.rs          |  7 +++++++
 crates/bevy_pbr/src/prepass/mod.rs       | 13 +++++++++++--
 crates/bevy_pbr/src/render/light.rs      |  4 ++++
 5 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/crates/bevy_material/src/lib.rs b/crates/bevy_material/src/lib.rs
index 296554085a129..fcb1375ea0a71 100644
--- a/crates/bevy_material/src/lib.rs
+++ b/crates/bevy_material/src/lib.rs
@@ -94,6 +94,8 @@ pub struct MaterialProperties {
     pub shadows_enabled: bool,
     /// Whether prepass is enabled for this material
     pub prepass_enabled: bool,
+    /// Whether prepass needs to read the material
+    pub prepass_reads_material: bool,
 }
 
 impl MaterialProperties {
diff --git a/crates/bevy_pbr/src/extended_material.rs b/crates/bevy_pbr/src/extended_material.rs
index 088a81f65cb2f..24f7e76372ef9 100644
--- a/crates/bevy_pbr/src/extended_material.rs
+++ b/crates/bevy_pbr/src/extended_material.rs
@@ -61,6 +61,11 @@ pub trait MaterialExtension: Asset + AsBindGroup + Clone + Sized {
         true
     }
 
+    #[inline]
+    fn prepass_reads_material() -> bool {
+        false
+    }
+
     /// Returns this material's prepass vertex shader. If [`ShaderRef::Default`] is returned, the base material prepass vertex shader
     /// will be used.
     fn prepass_vertex_shader() -> ShaderRef {
@@ -355,6 +360,10 @@ impl<B: Material, E: MaterialExtension> Material for ExtendedMaterial<B, E> {
         E::enable_shadows()
     }
 
+    fn prepass_reads_material() -> bool {
+        E::prepass_reads_material()
+    }
+
     fn prepass_vertex_shader() -> ShaderRef {
         match E::prepass_vertex_shader() {
             ShaderRef::Default => B::prepass_vertex_shader(),
diff --git a/crates/bevy_pbr/src/material.rs b/crates/bevy_pbr/src/material.rs
index 967ccda522ace..fb7fe28342e8a 100644
--- a/crates/bevy_pbr/src/material.rs
+++ b/crates/bevy_pbr/src/material.rs
@@ -200,6 +200,11 @@ pub trait Material: Asset + AsBindGroup + Clone + Sized {
         true
     }
 
+    #[inline]
+    fn prepass_reads_material() -> bool {
+        false
+    }
+
     /// Returns this material's prepass vertex shader. If [`ShaderRef::Default`] is returned, the default prepass vertex shader
     /// will be used.
     ///
@@ -1690,6 +1695,7 @@ where
 
         let shadows_enabled = M::enable_shadows();
         let prepass_enabled = M::enable_prepass();
+        let prepass_reads_material = M::prepass_reads_material();
 
         let draw_opaque_pbr = opaque_draw_functions.read().id::<DrawMaterial>();
         let draw_alpha_mask_pbr = alpha_mask_draw_functions.read().id::<DrawMaterial>();
@@ -1790,6 +1796,7 @@ where
                 material_key,
                 shadows_enabled,
                 prepass_enabled,
+                prepass_reads_material,
             }),
         })
     }
diff --git a/crates/bevy_pbr/src/prepass/mod.rs b/crates/bevy_pbr/src/prepass/mod.rs
index 85a7f813ba448..308d6195f50ac 100644
--- a/crates/bevy_pbr/src/prepass/mod.rs
+++ b/crates/bevy_pbr/src/prepass/mod.rs
@@ -386,7 +386,9 @@ impl SpecializedMeshPipeline for PrepassPipelineSpecializer {
 }
 
 fn is_depth_only_opaque_prepass(mesh_key: MeshPipelineKey) -> bool {
-    mesh_key.intersection(MeshPipelineKey::ALL_PREPASS_BITS) == MeshPipelineKey::DEPTH_PREPASS
+    !mesh_key.contains(MeshPipelineKey::PREPASS_READS_MATERIAL)
+        && mesh_key.intersection(MeshPipelineKey::ALL_PREPASS_BITS)
+            == MeshPipelineKey::DEPTH_PREPASS
 }
 
 impl PrepassPipeline {
@@ -421,7 +423,10 @@ impl PrepassPipeline {
         // or emulated by setting depth in the fragment shader for GPUs that don't support it natively.
         let emulate_unclipped_depth = mesh_key.contains(MeshPipelineKey::UNCLIPPED_DEPTH_ORTHO)
             && !self.depth_clip_control_supported;
-        if is_depth_only_opaque_prepass(mesh_key) && !emulate_unclipped_depth {
+        if is_depth_only_opaque_prepass(mesh_key)
+            && !emulate_unclipped_depth
+            && !material_properties.prepass_reads_material
+        {
             bind_group_layouts.push(self.empty_layout.clone());
         } else {
             bind_group_layouts.push(
@@ -1114,6 +1119,10 @@ pub(crate) fn specialize_prepass_material_meshes(
                     mesh_key |= MeshPipelineKey::VISIBILITY_RANGE_DITHER;
                 }
 
+                if material.properties.prepass_reads_material {
+                    mesh_key |= MeshPipelineKey::PREPASS_READS_MATERIAL;
+                }
+
                 // If the previous frame has skins or morph targets, note that.
                 if motion_vector_prepass.is_some() {
                     if mesh_instance
diff --git a/crates/bevy_pbr/src/render/light.rs b/crates/bevy_pbr/src/render/light.rs
index 0188614a17623..dd1ccabed4baf 100644
--- a/crates/bevy_pbr/src/render/light.rs
+++ b/crates/bevy_pbr/src/render/light.rs
@@ -2448,6 +2448,10 @@ pub(crate) fn specialize_shadows(
                     _ => MeshPipelineKey::NONE,
                 };
 
+                if material.properties.prepass_reads_material {
+                    mesh_key |= MeshPipelineKey::PREPASS_READS_MATERIAL;
+                }
+
                 work_items.push(ShadowSpecializationWorkItem {
                     visible_entity: *visible_entity,
                     retained_view_entity: extracted_view_light.retained_view_entity,