From 94b8ee481ff868636de9ffebcc9af20f83fa89a8 Mon Sep 17 00:00:00 2001
From: Ben Doherty <bendoherty@google.com>
Date: Mon, 11 Aug 2025 17:30:07 -0400
Subject: [PATCH] Fix: webgpu error regarding mismatched pipeline  (#9056)

---
 filament/src/RenderPass.cpp     |  3 ++-
 filament/src/details/Engine.cpp |  3 +++
 filament/src/details/Material.h | 14 ++++++++++++--
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/filament/src/RenderPass.cpp b/filament/src/RenderPass.cpp
index 26ebc37121..2d005f2dd1 100644
--- a/filament/src/RenderPass.cpp
+++ b/filament/src/RenderPass.cpp
@@ -1067,7 +1067,8 @@ void RenderPass::Executor::execute(FEngine const& engine, DriverApi& driver,
                     // Each material has a per-material descriptor-set layout which encodes the
                     // material's parameters (ubo and samplers)
                     pipeline.pipelineLayout.setLayout[+DescriptorSetBindingPoints::PER_MATERIAL] =
-                            ma->getDescriptorSetLayout().getHandle();
+                            ma->getDescriptorSetLayout(info.materialVariant).getHandle();
+
 
                     if (UTILS_UNLIKELY(ma->getMaterialDomain() == MaterialDomain::POST_PROCESS)) {
                         // It is possible to get a post-process material here (even though it's
diff --git a/filament/src/details/Engine.cpp b/filament/src/details/Engine.cpp
index 58fc61a6d0..f4d217cb04 100644
--- a/filament/src/details/Engine.cpp
+++ b/filament/src/details/Engine.cpp
@@ -465,6 +465,9 @@ void FEngine::init() {
         }
         mDefaultMaterial = downcast(defaultMaterialBuilder.build(*this));
     }
+    // We must commit the default material instance here. It may not be used in a scene, but its
+    // descriptor set may still be used for shared variants.
+    mDefaultMaterial->getDefaultInstance()->commit(driverApi);
 
     if (UTILS_UNLIKELY(getSupportedFeatureLevel() >= FeatureLevel::FEATURE_LEVEL_1)) {
         mDefaultColorGrading = downcast(ColorGrading::Builder().build(*this));
diff --git a/filament/src/details/Material.h b/filament/src/details/Material.h
index 850a3d8ec8..a7eb90e65e 100644
--- a/filament/src/details/Material.h
+++ b/filament/src/details/Material.h
@@ -96,8 +96,18 @@ public:
     DescriptorSetLayout const& getPerViewDescriptorSetLayout(
             Variant const variant, bool const useVsmDescriptorSetLayout) const noexcept;
 
-    DescriptorSetLayout const& getDescriptorSetLayout() const noexcept {
-        return mDescriptorSetLayout;
+    // Returns the layout that should be used when this material is bound to the pipeline for the
+    // given variant. Shared variants use the Engine's default material's variants, so we should
+    // also use the default material's layout.
+    DescriptorSetLayout const& getDescriptorSetLayout(Variant variant = {}) const noexcept {
+        if (!isSharedVariant(variant)) {
+            return mDescriptorSetLayout;
+        }
+        FMaterial const* const pDefaultMaterial = mEngine.getDefaultMaterial();
+        if (UTILS_UNLIKELY(!pDefaultMaterial)) {
+            return mDescriptorSetLayout;
+        }
+        return pDefaultMaterial->getDescriptorSetLayout();
     }
 
     void compile(CompilerPriorityQueue priority,