Gracefully fallback to not using MSAA when normal MSAA is not supported.

Author: bdero

lib/gpu/context.cc

@@ -10,11 +10,18 @@
 #include "flutter/lib/ui/ui_dart_state.h"
 #include "fml/make_copyable.h"
 #include "impeller/core/platform.h"
+#include "impeller/renderer/context.h"
 #include "tonic/converter/dart_converter.h"
 
 namespace flutter {
 namespace gpu {
 
+bool SupportsNormalOffscreenMSAA(const impeller::Context& context) {
+  auto& capabilities = context.GetCapabilities();
+  return capabilities->SupportsOffscreenMSAA() &&
+         !capabilities->SupportsImplicitResolvingMSAA();
+}
+
 IMPLEMENT_WRAPPERTYPEINFO(flutter_gpu, Context);
 
 std::shared_ptr<impeller::Context> Context::default_context_;
@@ -114,5 +121,5 @@ extern int InternalFlutterGpu_Context_GetMinimumUniformByteAlignment(
 
 extern bool InternalFlutterGpu_Context_GetSupportsOffscreenMSAA(
     flutter::gpu::Context* wrapper) {
-  return wrapper->GetContext()->GetCapabilities()->SupportsOffscreenMSAA();
+  return flutter::gpu::SupportsNormalOffscreenMSAA(*wrapper->GetContext());
 }

lib/gpu/context.h

@@ -13,6 +13,8 @@
 namespace flutter {
 namespace gpu {
 
+bool SupportsNormalOffscreenMSAA(const impeller::Context& context);
+
 class Context : public RefCountedDartWrappable<Context> {
   DEFINE_WRAPPERTYPEINFO();
   FML_FRIEND_MAKE_REF_COUNTED(Context);

lib/gpu/render_pass.cc

@@ -20,6 +20,7 @@
 #include "impeller/renderer/pipeline.h"
 #include "impeller/renderer/pipeline_descriptor.h"
 #include "impeller/renderer/pipeline_library.h"
+#include "lib/gpu/context.h"
 #include "lib/ui/ui_dart_state.h"
 #include "tonic/converter/dart_converter.h"
 
@@ -242,6 +243,14 @@ Dart_Handle InternalFlutterGpu_RenderPass_SetColorAttachment(
         tonic::DartConverter<flutter::gpu::Texture*>::FromDart(
             resolve_texture_wrapper);
     desc.resolve_texture = resolve_texture->GetTexture();
+
+    // If the backend doesn't support normal MSAA, gracefully fallback to
+    // rendering without MSAA.
+    if (!flutter::gpu::SupportsNormalOffscreenMSAA(*wrapper->GetContext())) {
+      desc.texture = desc.resolve_texture;
+      desc.resolve_texture = nullptr;
+      desc.store_action = impeller::StoreAction::kStore;
+    }
   }
   wrapper->GetRenderTarget().SetColorAttachment(desc, color_attachment_index);
   return Dart_Null();