[Impeller] Store the root stencil on iOS

impeller/entity/entity_pass.cc

@@ -148,6 +148,15 @@ EntityPass* EntityPass::AddSubpass(std::unique_ptr<EntityPass> pass) {
   return subpass_pointer;
 }
 
+static RenderTarget::AttachmentConfig GetDefaultStencilConfig(bool readable) {
+  return RenderTarget::AttachmentConfig{
+      .storage_mode = readable ? StorageMode::kDevicePrivate
+                               : StorageMode::kDeviceTransient,
+      .load_action = LoadAction::kDontCare,
+      .store_action = StoreAction::kDontCare,
+  };
+}
+
 static EntityPassTarget CreateRenderTarget(ContentContext& renderer,
                                            ISize size,
                                            bool readable,
@@ -170,13 +179,8 @@ static EntityPassTarget CreateRenderTarget(ContentContext& renderer,
             .resolve_storage_mode = StorageMode::kDevicePrivate,
             .load_action = LoadAction::kDontCare,
             .store_action = StoreAction::kMultisampleResolve,
-            .clear_color = clear_color},  // color_attachment_config
-        RenderTarget::AttachmentConfig{
-            .storage_mode = readable ? StorageMode::kDevicePrivate
-                                     : StorageMode::kDeviceTransient,
-            .load_action = LoadAction::kDontCare,
-            .store_action = StoreAction::kDontCare,
-        }  // stencil_attachment_config
+            .clear_color = clear_color},   // color_attachment_config
+        GetDefaultStencilConfig(readable)  // stencil_attachment_config
     );
   } else {
     target = RenderTarget::CreateOffscreen(
@@ -187,13 +191,8 @@ static EntityPassTarget CreateRenderTarget(ContentContext& renderer,
             .storage_mode = StorageMode::kDevicePrivate,
             .load_action = LoadAction::kDontCare,
             .store_action = StoreAction::kDontCare,
-        },  // color_attachment_config
-        RenderTarget::AttachmentConfig{
-            .storage_mode = readable ? StorageMode::kDevicePrivate
-                                     : StorageMode::kDeviceTransient,
-            .load_action = LoadAction::kDontCare,
-            .store_action = StoreAction::kDontCare,
-        }  // stencil_attachment_config
+        },                                 // color_attachment_config
+        GetDefaultStencilConfig(readable)  // stencil_attachment_config
     );
   }
 
@@ -215,16 +214,28 @@ bool EntityPass::Render(ContentContext& renderer,
     return false;
   }
 
+  if (!render_target.GetStencilAttachment().has_value()) {
+    VALIDATION_LOG << "The root RenderTarget must have a stencil attachment.";
+    return false;
+  }
+
+  auto stencil_texture = render_target.GetStencilAttachment()->texture;
+  if (!stencil_texture) {
+    VALIDATION_LOG << "The root RenderTarget must have a stencil texture.";
+    return false;
+  }
+
   StencilCoverageStack stencil_coverage_stack = {StencilCoverageLayer{
       .coverage = Rect::MakeSize(render_target.GetRenderTargetSize()),
       .stencil_depth = 0}};
 
-  //
   bool supports_root_pass_reads =
       renderer.GetDeviceCapabilities().SupportsReadFromOnscreenTexture() &&
       // If the backend doesn't have `SupportsReadFromResolve`, we need to flip
       // between two textures when restoring a previous MSAA pass.
-      renderer.GetDeviceCapabilities().SupportsReadFromResolve();
+      renderer.GetDeviceCapabilities().SupportsReadFromResolve() &&
+      stencil_texture->GetTextureDescriptor().storage_mode !=
+          StorageMode::kDeviceTransient;
   if (!supports_root_pass_reads && GetTotalPassReads(renderer) > 0) {
     auto offscreen_target =
         CreateRenderTarget(renderer, render_target.GetRenderTargetSize(), true,

impeller/renderer/backend/metal/surface_mtl.mm

@@ -83,7 +83,7 @@
   color0.resolve_texture = resolve_tex;
 
   TextureDescriptor stencil_tex_desc;
-  stencil_tex_desc.storage_mode = StorageMode::kDeviceTransient;
+  stencil_tex_desc.storage_mode = StorageMode::kDevicePrivate;
   stencil_tex_desc.type = TextureType::kTexture2DMultisample;
   stencil_tex_desc.sample_count = SampleCount::kCount4;
   stencil_tex_desc.format =

impeller/renderer/backend/vulkan/surface_vk.cc

@@ -61,8 +61,8 @@ std::unique_ptr<SurfaceVK> SurfaceVK::WrapSwapchainImage(
   color0.resolve_texture = resolve_tex;
 
   TextureDescriptor stencil0_tex;
-  stencil0_tex.storage_mode = StorageMode::kDeviceTransient;
-  stencil0_tex.type = TextureType::kTexture2D;
+  stencil0_tex.storage_mode = StorageMode::kDevicePrivate;
+  stencil0_tex.type = TextureType::kTexture2DMultisample;
   stencil0_tex.sample_count = SampleCount::kCount4;
   stencil0_tex.format = context->GetCapabilities()->GetDefaultStencilFormat();
   stencil0_tex.size = msaa_tex_desc.size;

impeller/renderer/render_target.cc

@@ -239,25 +239,8 @@ RenderTarget RenderTarget::CreateOffscreen(
   target.SetColorAttachment(color0, 0u);
 
   if (stencil_attachment_config.has_value()) {
-    TextureDescriptor stencil_tex0;
-    stencil_tex0.storage_mode = stencil_attachment_config->storage_mode;
-    stencil_tex0.format = context.GetCapabilities()->GetDefaultStencilFormat();
-    stencil_tex0.size = size;
-    stencil_tex0.usage =
-        static_cast<TextureUsageMask>(TextureUsage::kRenderTarget);
-
-    StencilAttachment stencil0;
-    stencil0.load_action = stencil_attachment_config->load_action;
-    stencil0.store_action = stencil_attachment_config->store_action;
-    stencil0.clear_stencil = 0u;
-    stencil0.texture =
-        context.GetResourceAllocator()->CreateTexture(stencil_tex0);
-
-    if (!stencil0.texture) {
-      return {};
-    }
-    stencil0.texture->SetLabel(SPrintF("%s Stencil Texture", label.c_str()));
-    target.SetStencilAttachment(std::move(stencil0));
+    target.SetupStencilAttachment(context, size, false, label,
+                                  stencil_attachment_config.value());
   } else {
     target.SetStencilAttachment(std::nullopt);
   }
@@ -331,34 +314,46 @@ RenderTarget RenderTarget::CreateOffscreenMSAA(
   // Create MSAA stencil texture.
 
   if (stencil_attachment_config.has_value()) {
-    TextureDescriptor stencil_tex0;
-    stencil_tex0.storage_mode = stencil_attachment_config->storage_mode;
-    stencil_tex0.type = TextureType::kTexture2DMultisample;
-    stencil_tex0.sample_count = SampleCount::kCount4;
-    stencil_tex0.format = context.GetCapabilities()->GetDefaultStencilFormat();
-    stencil_tex0.size = size;
-    stencil_tex0.usage =
-        static_cast<TextureUsageMask>(TextureUsage::kRenderTarget);
-
-    StencilAttachment stencil0;
-    stencil0.load_action = stencil_attachment_config->load_action;
-    stencil0.store_action = stencil_attachment_config->store_action;
-    stencil0.clear_stencil = 0u;
-    stencil0.texture =
-        context.GetResourceAllocator()->CreateTexture(stencil_tex0);
-
-    if (!stencil0.texture) {
-      return {};
-    }
-    stencil0.texture->SetLabel(SPrintF("%s Stencil Texture", label.c_str()));
-    target.SetStencilAttachment(std::move(stencil0));
+    target.SetupStencilAttachment(context, size, true, label,
+                                  stencil_attachment_config.value());
   } else {
     target.SetStencilAttachment(std::nullopt);
   }
 
   return target;
 }
 
+void RenderTarget::SetupStencilAttachment(
+    const Context& context,
+    ISize size,
+    bool msaa,
+    const std::string& label,
+    AttachmentConfig stencil_attachment_config) {
+  TextureDescriptor stencil_tex0;
+  stencil_tex0.storage_mode = stencil_attachment_config.storage_mode;
+  if (msaa) {
+    stencil_tex0.type = TextureType::kTexture2DMultisample;
+    stencil_tex0.sample_count = SampleCount::kCount4;
+  }
+  stencil_tex0.format = context.GetCapabilities()->GetDefaultStencilFormat();
+  stencil_tex0.size = size;
+  stencil_tex0.usage =
+      static_cast<TextureUsageMask>(TextureUsage::kRenderTarget);
+
+  StencilAttachment stencil0;
+  stencil0.load_action = stencil_attachment_config.load_action;
+  stencil0.store_action = stencil_attachment_config.store_action;
+  stencil0.clear_stencil = 0u;
+  stencil0.texture =
+      context.GetResourceAllocator()->CreateTexture(stencil_tex0);
+
+  if (!stencil0.texture) {
+    return;  // Error messages are handled by `Allocator::CreateTexture`.
+  }
+  stencil0.texture->SetLabel(SPrintF("%s Stencil Texture", label.c_str()));
+  SetStencilAttachment(std::move(stencil0));
+}
+
 size_t RenderTarget::GetTotalAttachmentCount() const {
   size_t count = 0u;
   for (const auto& [_, color] : colors_) {

impeller/renderer/render_target.h

@@ -76,6 +76,13 @@ class RenderTarget final {
 
   bool IsValid() const;
 
+  void SetupStencilAttachment(const Context& context,
+                              ISize size,
+                              bool msaa,
+                              const std::string& label = "Offscreen",
+                              AttachmentConfig stencil_attachment_config =
+                                  kDefaultStencilAttachmentConfig);
+
   SampleCount GetSampleCount() const;
 
   bool HasColorAttachment(size_t index) const;