impeller/entity/entity_pass.cc - mirrors/engine - Git at Google

 // Copyright 2013 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #include "impeller/entity/entity_pass.h"

 #include <memory>
 #include <utility>
 #include <variant>

 #include "flutter/fml/logging.h"
 #include "flutter/fml/macros.h"
 #include "flutter/fml/trace_event.h"
 #include "impeller/base/validation.h"
 #include "impeller/entity/contents/content_context.h"
 #include "impeller/entity/contents/filters/color_filter_contents.h"
 #include "impeller/entity/contents/filters/inputs/filter_input.h"
 #include "impeller/entity/contents/texture_contents.h"
 #include "impeller/entity/entity.h"
 #include "impeller/entity/inline_pass_context.h"
 #include "impeller/geometry/path_builder.h"
 #include "impeller/renderer/allocator.h"
 #include "impeller/renderer/command.h"
 #include "impeller/renderer/command_buffer.h"
 #include "impeller/renderer/formats.h"
 #include "impeller/renderer/render_pass.h"
 #include "impeller/renderer/texture.h"

 namespace impeller {

 EntityPass::EntityPass() = default;

 EntityPass::~EntityPass() = default;

 void EntityPass::SetDelegate(std::unique_ptr<EntityPassDelegate> delegate) {
   if (!delegate) {
     return;
   }
   delegate_ = std::move(delegate);
 }

 void EntityPass::AddEntity(Entity entity) {
   if (entity.GetBlendMode() > Entity::kLastPipelineBlendMode) {
     reads_from_pass_texture_ += 1;
   }

   elements_.emplace_back(std::move(entity));
 }

 void EntityPass::SetElements(std::vector<Element> elements) {
   elements_ = std::move(elements);
 }

 size_t EntityPass::GetSubpassesDepth() const {
   size_t max_subpass_depth = 0u;
   for (const auto& element : elements_) {
     if (auto subpass = std::get_if<std::unique_ptr<EntityPass>>(&element)) {
       max_subpass_depth =
           std::max(max_subpass_depth, subpass->get()->GetSubpassesDepth());
     }
   }
   return max_subpass_depth + 1u;
 }

 const std::shared_ptr<LazyGlyphAtlas>& EntityPass::GetLazyGlyphAtlas() const {
   return lazy_glyph_atlas_;
 }

 std::optional<Rect> EntityPass::GetElementsCoverage(
     std::optional<Rect> coverage_crop) const {
   std::optional<Rect> result;
   for (const auto& element : elements_) {
     std::optional<Rect> coverage;

     if (auto entity = std::get_if<Entity>(&element)) {
       coverage = entity->GetCoverage();

       if (coverage.has_value() && coverage_crop.has_value()) {
         coverage = coverage->Intersection(coverage_crop.value());
       }
     } else if (auto subpass =
                    std::get_if<std::unique_ptr<EntityPass>>(&element)) {
       coverage = GetSubpassCoverage(*subpass->get(), coverage_crop);
     } else {
       FML_UNREACHABLE();
     }

     if (!result.has_value() && coverage.has_value()) {
       result = coverage;
       continue;
     }
     if (!coverage.has_value()) {
       continue;
     }
     result = result->Union(coverage.value());
   }
   return result;
 }

 std::optional<Rect> EntityPass::GetSubpassCoverage(
     const EntityPass& subpass,
     std::optional<Rect> coverage_clip) const {
   auto entities_coverage = subpass.GetElementsCoverage(coverage_clip);
   // The entities don't cover anything. There is nothing to do.
   if (!entities_coverage.has_value()) {
     return std::nullopt;
   }

   // The delegates don't have an opinion on what the entity coverage has to be.
   // Just use that as-is.
   auto delegate_coverage = subpass.delegate_->GetCoverageRect();
   if (!delegate_coverage.has_value()) {
     return entities_coverage;
   }
   // The delegate coverage hint is in given in local space, so apply the subpass
   // transformation.
   delegate_coverage = delegate_coverage->TransformBounds(subpass.xformation_);

   // If the delegate tells us the coverage is smaller than it needs to be, then
   // great. OTOH, if the delegate is being wasteful, limit coverage to what is
   // actually needed.
   return entities_coverage->Intersection(delegate_coverage.value());
 }

 EntityPass* EntityPass::GetSuperpass() const {
   return superpass_;
 }

 EntityPass* EntityPass::AddSubpass(std::unique_ptr<EntityPass> pass) {
   if (!pass) {
     return nullptr;
   }
   FML_DCHECK(pass->superpass_ == nullptr);
   pass->superpass_ = this;

   if (pass->blend_mode_ > Entity::kLastPipelineBlendMode ||
       pass->backdrop_filter_proc_.has_value()) {
     reads_from_pass_texture_ += 1;
   }

   auto subpass_pointer = pass.get();
   elements_.emplace_back(std::move(pass));
   return subpass_pointer;
 }

 static RenderTarget CreateRenderTarget(ContentContext& renderer,
                                        ISize size,
                                        bool readable) {
   auto context = renderer.GetContext();

   /// All of the load/store actions are managed by `InlinePassContext` when
   /// `RenderPasses` are created, so we just set them to `kDontCare` here.
   /// What's important is the `StorageMode` of the textures, which cannot be
   /// changed for the lifetime of the textures.

   if (context->SupportsOffscreenMSAA()) {
     return RenderTarget::CreateOffscreenMSAA(
         *context,                          // context
         size,                              // size
         "EntityPass",                      // label
         StorageMode::kDeviceTransient,     // color_storage_mode
         StorageMode::kDevicePrivate,       // color_resolve_storage_mode
         LoadAction::kDontCare,             // color_load_action
         StoreAction::kMultisampleResolve,  // color_store_action
         readable ? StorageMode::kDevicePrivate
                  : StorageMode::kDeviceTransient,  // stencil_storage_mode
         LoadAction::kDontCare,                     // stencil_load_action
         StoreAction::kDontCare                     // stencil_store_action
     );
   }

   return RenderTarget::CreateOffscreen(
       *context,                     // context
       size,                         // size
       "EntityPass",                 // label
       StorageMode::kDevicePrivate,  // color_storage_mode
       LoadAction::kDontCare,        // color_load_action
       StoreAction::kDontCare,       // color_store_action
       readable ? StorageMode::kDevicePrivate
                : StorageMode::kDeviceTransient,  // stencil_storage_mode
       LoadAction::kDontCare,                     // stencil_load_action
       StoreAction::kDontCare                     // stencil_store_action
   );
 }

 bool EntityPass::Render(ContentContext& renderer,
                         const RenderTarget& render_target) const {
   if (reads_from_pass_texture_ > 0) {
     auto offscreen_target =
         CreateRenderTarget(renderer, render_target.GetRenderTargetSize(), true);
     if (!OnRender(renderer, offscreen_target.GetRenderTargetSize(),
                   offscreen_target, Point(), Point(), 0)) {
       return false;
     }

     auto command_buffer = renderer.GetContext()->CreateCommandBuffer();
     command_buffer->SetLabel("EntityPass Root Command Buffer");
     auto render_pass = command_buffer->CreateRenderPass(render_target);
     render_pass->SetLabel("EntityPass Root Render Pass");

     {
       auto size_rect = Rect::MakeSize(offscreen_target.GetRenderTargetSize());
       auto contents = TextureContents::MakeRect(size_rect);
       contents->SetTexture(offscreen_target.GetRenderTargetTexture());
       contents->SetSourceRect(size_rect);

       Entity entity;
       entity.SetContents(contents);
       entity.SetBlendMode(BlendMode::kSource);

       entity.Render(renderer, *render_pass);
     }

     if (!render_pass->EncodeCommands()) {
       return false;
     }
     if (!command_buffer->SubmitCommands()) {
       return false;
     }

     return true;
   }

   return OnRender(renderer, render_target.GetRenderTargetSize(), render_target,
                   Point(), Point(), 0);
 }

 EntityPass::EntityResult EntityPass::GetEntityForElement(
     const EntityPass::Element& element,
     ContentContext& renderer,
     InlinePassContext& pass_context,
     ISize root_pass_size,
     Point position,
     uint32_t pass_depth,
     size_t stencil_depth_floor) const {
   Entity element_entity;

   //--------------------------------------------------------------------------
   /// Setup entity element.
   ///

   if (const auto& entity = std::get_if<Entity>(&element)) {
     element_entity = *entity;
     if (!position.IsZero()) {
       // If the pass image is going to be rendered with a non-zero position,
       // apply the negative translation to entity copies before rendering them
       // so that they'll end up rendering to the correct on-screen position.
       element_entity.SetTransformation(
           Matrix::MakeTranslation(Vector3(-position)) *
           element_entity.GetTransformation());
     }
   }

   //--------------------------------------------------------------------------
   /// Setup subpass element.
   ///

   else if (const auto& subpass_ptr =
                std::get_if<std::unique_ptr<EntityPass>>(&element)) {
     auto subpass = subpass_ptr->get();

     if (subpass->delegate_->CanElide()) {
       return EntityPass::EntityResult::Skip();
     }

     if (subpass->delegate_->CanCollapseIntoParentPass() &&
         !subpass->backdrop_filter_proc_.has_value()) {
       // Directly render into the parent target and move on.
       if (!subpass->OnRender(renderer, root_pass_size,
                              pass_context.GetRenderTarget(), position, position,
                              stencil_depth_floor)) {
         return EntityPass::EntityResult::Failure();
       }
       return EntityPass::EntityResult::Skip();
     }

     std::shared_ptr<Contents> backdrop_filter_contents = nullptr;
     if (subpass->backdrop_filter_proc_.has_value()) {
       auto texture = pass_context.GetTexture();
       // Render the backdrop texture before any of the pass elements.
       const auto& proc = subpass->backdrop_filter_proc_.value();
       backdrop_filter_contents =
           proc(FilterInput::Make(std::move(texture)), subpass->xformation_);

       // The subpass will need to read from the current pass texture when
       // rendering the backdrop, so if there's an active pass, end it prior to
       // rendering the subpass.
       pass_context.EndPass();
     }

     auto subpass_coverage =
         GetSubpassCoverage(*subpass, Rect::MakeSize(root_pass_size));
     if (subpass->cover_whole_screen_) {
       subpass_coverage = Rect(
           position, Size(pass_context.GetRenderTarget().GetRenderTargetSize()));
     }
     if (backdrop_filter_contents) {
       auto backdrop_coverage = backdrop_filter_contents->GetCoverage(Entity{});
       if (backdrop_coverage.has_value()) {
         backdrop_coverage->origin += position;

         if (subpass_coverage.has_value()) {
           subpass_coverage = subpass_coverage->Union(backdrop_coverage.value());
         } else {
           subpass_coverage = backdrop_coverage;
         }
       }
     }

     if (subpass_coverage.has_value()) {
       subpass_coverage =
           subpass_coverage->Intersection(Rect::MakeSize(root_pass_size));
     }

     if (!subpass_coverage.has_value()) {
       return EntityPass::EntityResult::Skip();
     }

     if (subpass_coverage->size.IsEmpty()) {
       // It is not an error to have an empty subpass. But subpasses that can't
       // create their intermediates must trip errors.
       return EntityPass::EntityResult::Skip();
     }

     RenderTarget subpass_target;
     if (subpass->reads_from_pass_texture_ > 0) {
       subpass_target = CreateRenderTarget(
           renderer, ISize::Ceil(subpass_coverage->size), true);
     } else {
       subpass_target = CreateRenderTarget(
           renderer, ISize::Ceil(subpass_coverage->size), false);
     }

     auto subpass_texture = subpass_target.GetRenderTargetTexture();

     if (!subpass_texture) {
       return EntityPass::EntityResult::Failure();
     }

     auto offscreen_texture_contents =
         subpass->delegate_->CreateContentsForSubpassTarget(
             subpass_texture, subpass->xformation_);

     if (!offscreen_texture_contents) {
       // This is an error because the subpass delegate said the pass couldn't
       // be collapsed into its parent. Yet, when asked how it want's to
       // postprocess the offscreen texture, it couldn't give us an answer.
       //
       // Theoretically, we could collapse the pass now. But that would be
       // wasteful as we already have the offscreen texture and we don't want
       // to discard it without ever using it. Just make the delegate do the
       // right thing.
       return EntityPass::EntityResult::Failure();
     }

     // Stencil textures aren't shared between EntityPasses (as much of the
     // time they are transient).
     if (!subpass->OnRender(renderer, root_pass_size, subpass_target,
                            subpass_coverage->origin, position, ++pass_depth,
                            subpass->stencil_depth_, backdrop_filter_contents)) {
       return EntityPass::EntityResult::Failure();
     }

     element_entity.SetContents(std::move(offscreen_texture_contents));
     element_entity.SetStencilDepth(subpass->stencil_depth_);
     element_entity.SetBlendMode(subpass->blend_mode_);
     element_entity.SetTransformation(
         Matrix::MakeTranslation(Vector3(subpass_coverage->origin - position)));
   } else {
     FML_UNREACHABLE();
   }

   return EntityPass::EntityResult::Success(element_entity);
 }

 struct StencilLayer {
   std::optional<Rect> coverage;
   size_t stencil_depth;
 };

 bool EntityPass::OnRender(
     ContentContext& renderer,
     ISize root_pass_size,
     const RenderTarget& render_target,
     Point position,
     Point parent_position,
     uint32_t pass_depth,
     size_t stencil_depth_floor,
     std::shared_ptr<Contents> backdrop_filter_contents) const {
   TRACE_EVENT0("impeller", "EntityPass::OnRender");

   auto context = renderer.GetContext();
   InlinePassContext pass_context(context, render_target,
                                  reads_from_pass_texture_);
   if (!pass_context.IsValid()) {
     return false;
   }

   std::vector<StencilLayer> stencil_stack = {StencilLayer{
       .coverage = Rect::MakeSize(render_target.GetRenderTargetSize()),
       .stencil_depth = stencil_depth_floor}};

   auto render_element = [&stencil_depth_floor, &pass_context, &pass_depth,
                          &renderer, &stencil_stack](Entity& element_entity) {
     auto result = pass_context.GetRenderPass(pass_depth);

     if (!result.pass) {
       return false;
     }

     // If the pass context returns a texture, we need to draw it to the current
     // pass. We do this because it's faster and takes significantly less memory
     // than storing/loading large MSAA textures.
     if (result.backdrop_texture) {
       auto size_rect = Rect::MakeSize(result.pass->GetRenderTargetSize());
       auto msaa_backdrop_contents = TextureContents::MakeRect(size_rect);
       msaa_backdrop_contents->SetStencilEnabled(false);
       msaa_backdrop_contents->SetLabel("MSAA backdrop");
       msaa_backdrop_contents->SetSourceRect(size_rect);
       msaa_backdrop_contents->SetTexture(result.backdrop_texture);

       Entity msaa_backdrop_entity;
       msaa_backdrop_entity.SetContents(std::move(msaa_backdrop_contents));
       msaa_backdrop_entity.SetBlendMode(BlendMode::kSource);
       if (!msaa_backdrop_entity.Render(renderer, *result.pass)) {
         return false;
       }
     }

     if (!element_entity.ShouldRender(stencil_stack.back().coverage)) {
       return true;  // Nothing to render.
     }

     auto stencil_coverage =
         element_entity.GetStencilCoverage(stencil_stack.back().coverage);

     switch (stencil_coverage.type) {
       case Contents::StencilCoverage::Type::kNone:
         break;
       case Contents::StencilCoverage::Type::kAppend: {
         auto op = stencil_stack.back().coverage;
         stencil_stack.push_back(StencilLayer{
             .coverage = stencil_coverage.coverage,
             .stencil_depth = element_entity.GetStencilDepth() + 1});

         if (!op.has_value()) {
           // Running this append op won't impact the stencil because the whole
           // screen is already being clipped, so skip it.
           return true;
         }
       } break;
       case Contents::StencilCoverage::Type::kRestore: {
         if (stencil_stack.back().stencil_depth <=
             element_entity.GetStencilDepth()) {
           // Drop stencil restores that will do nothing.
           return true;
         }

         FML_DCHECK(stencil_stack.size() > 1);

         stencil_stack.pop_back();

         if (!stencil_stack.back().coverage.has_value()) {
           // Running this restore op won't make anything renderable, so skip it.
           return true;
         }
       } break;
     }

     element_entity.SetStencilDepth(element_entity.GetStencilDepth() -
                                    stencil_depth_floor);
     if (!element_entity.Render(renderer, *result.pass)) {
       return false;
     }
     return true;
   };

   if (backdrop_filter_proc_.has_value()) {
     if (!backdrop_filter_contents) {
       return false;
     }

     Entity backdrop_entity;
     backdrop_entity.SetContents(std::move(backdrop_filter_contents));
     backdrop_entity.SetTransformation(
         Matrix::MakeTranslation(Vector3(parent_position - position)));
     backdrop_entity.SetStencilDepth(stencil_depth_floor);

     render_element(backdrop_entity);
   }

   for (const auto& element : elements_) {
     EntityResult result =
         GetEntityForElement(element, renderer, pass_context, root_pass_size,
                             position, pass_depth, stencil_depth_floor);

     switch (result.status) {
       case EntityResult::kSuccess:
         break;
       case EntityResult::kFailure:
         return false;
       case EntityResult::kSkip:
         continue;
     };

     //--------------------------------------------------------------------------
     /// Setup advanced blends.
     ///

     if (result.entity.GetBlendMode() > Entity::kLastPipelineBlendMode) {
       // End the active pass and flush the buffer before rendering "advanced"
       // blends. Advanced blends work by binding the current render target
       // texture as an input ("destination"), blending with a second texture
       // input ("source"), writing the result to an intermediate texture, and
       // finally copying the data from the intermediate texture back to the
       // render target texture. And so all of the commands that have written
       // to the render target texture so far need to execute before it's bound
       // for blending (otherwise the blend pass will end up executing before
       // all the previous commands in the active pass).
       if (!pass_context.EndPass()) {
         return false;
       }

       // Amend an advanced blend filter to the contents, attaching the pass
       // texture.
       auto texture = pass_context.GetTexture();
       if (!texture) {
         return false;
       }

       FilterInput::Vector inputs = {
           FilterInput::Make(result.entity.GetContents()),
           FilterInput::Make(texture,
                             result.entity.GetTransformation().Invert())};
       auto contents =
           ColorFilterContents::MakeBlend(result.entity.GetBlendMode(), inputs);
       contents->SetCoverageCrop(result.entity.GetCoverage());
       result.entity.SetContents(std::move(contents));
       result.entity.SetBlendMode(BlendMode::kSource);
     }

     //--------------------------------------------------------------------------
     /// Render the Element.
     ///

     if (!render_element(result.entity)) {
       return false;
     }
   }

   return true;
 }

 void EntityPass::IterateAllEntities(
     const std::function<bool(Entity&)>& iterator) {
   if (!iterator) {
     return;
   }

   for (auto& element : elements_) {
     if (auto entity = std::get_if<Entity>(&element)) {
       if (!iterator(*entity)) {
         return;
       }
       continue;
     }
     if (auto subpass = std::get_if<std::unique_ptr<EntityPass>>(&element)) {
       subpass->get()->IterateAllEntities(iterator);
       continue;
     }
     FML_UNREACHABLE();
   }
 }

 std::unique_ptr<EntityPass> EntityPass::Clone() const {
   std::vector<Element> new_elements;
   new_elements.reserve(elements_.size());

   for (const auto& element : elements_) {
     if (auto entity = std::get_if<Entity>(&element)) {
       new_elements.push_back(*entity);
       continue;
     }
     if (auto subpass = std::get_if<std::unique_ptr<EntityPass>>(&element)) {
       new_elements.push_back(subpass->get()->Clone());
       continue;
     }
     FML_UNREACHABLE();
   }

   auto pass = std::make_unique<EntityPass>();
   pass->SetElements(std::move(new_elements));
   return pass;
 }

 void EntityPass::SetTransformation(Matrix xformation) {
   xformation_ = xformation;
 }

 void EntityPass::SetStencilDepth(size_t stencil_depth) {
   stencil_depth_ = stencil_depth;
 }

 void EntityPass::SetBlendMode(BlendMode blend_mode) {
   blend_mode_ = blend_mode;
   cover_whole_screen_ = Entity::BlendModeShouldCoverWholeScreen(blend_mode);
 }

 void EntityPass::SetBackdropFilter(std::optional<BackdropFilterProc> proc) {
   if (superpass_) {
     VALIDATION_LOG << "Backdrop filters cannot be set on EntityPasses that "
                       "have already been appended to another pass.";
   }

   backdrop_filter_proc_ = std::move(proc);
 }

 }  // namespace impeller
	// Copyright 2013 The Flutter Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#include "impeller/entity/entity_pass.h"

	#include <memory>
	#include <utility>
	#include <variant>

	#include "flutter/fml/logging.h"
	#include "flutter/fml/macros.h"
	#include "flutter/fml/trace_event.h"
	#include "impeller/base/validation.h"
	#include "impeller/entity/contents/content_context.h"
	#include "impeller/entity/contents/filters/color_filter_contents.h"
	#include "impeller/entity/contents/filters/inputs/filter_input.h"
	#include "impeller/entity/contents/texture_contents.h"
	#include "impeller/entity/entity.h"
	#include "impeller/entity/inline_pass_context.h"
	#include "impeller/geometry/path_builder.h"
	#include "impeller/renderer/allocator.h"
	#include "impeller/renderer/command.h"
	#include "impeller/renderer/command_buffer.h"
	#include "impeller/renderer/formats.h"
	#include "impeller/renderer/render_pass.h"
	#include "impeller/renderer/texture.h"

	namespace impeller {

	EntityPass::EntityPass() = default;

	EntityPass::~EntityPass() = default;

	void EntityPass::SetDelegate(std::unique_ptr<EntityPassDelegate> delegate) {
	if (!delegate) {
	return;
	}
	delegate_ = std::move(delegate);
	}

	void EntityPass::AddEntity(Entity entity) {
	if (entity.GetBlendMode() > Entity::kLastPipelineBlendMode) {
	reads_from_pass_texture_ += 1;
	}

	elements_.emplace_back(std::move(entity));
	}

	void EntityPass::SetElements(std::vector<Element> elements) {
	elements_ = std::move(elements);
	}

	size_t EntityPass::GetSubpassesDepth() const {
	size_t max_subpass_depth = 0u;
	for (const auto& element : elements_) {
	if (auto subpass = std::get_if<std::unique_ptr<EntityPass>>(&element)) {
	max_subpass_depth =
	std::max(max_subpass_depth, subpass->get()->GetSubpassesDepth());
	}
	}
	return max_subpass_depth + 1u;
	}

	const std::shared_ptr<LazyGlyphAtlas>& EntityPass::GetLazyGlyphAtlas() const {
	return lazy_glyph_atlas_;
	}

	std::optional<Rect> EntityPass::GetElementsCoverage(
	std::optional<Rect> coverage_crop) const {
	std::optional<Rect> result;
	for (const auto& element : elements_) {
	std::optional<Rect> coverage;

	if (auto entity = std::get_if<Entity>(&element)) {
	coverage = entity->GetCoverage();

	if (coverage.has_value() && coverage_crop.has_value()) {
	coverage = coverage->Intersection(coverage_crop.value());
	}
	} else if (auto subpass =
	std::get_if<std::unique_ptr<EntityPass>>(&element)) {
	coverage = GetSubpassCoverage(*subpass->get(), coverage_crop);
	} else {
	FML_UNREACHABLE();
	}

	if (!result.has_value() && coverage.has_value()) {
	result = coverage;
	continue;
	}
	if (!coverage.has_value()) {
	continue;
	}
	result = result->Union(coverage.value());
	}
	return result;
	}

	std::optional<Rect> EntityPass::GetSubpassCoverage(
	const EntityPass& subpass,
	std::optional<Rect> coverage_clip) const {
	auto entities_coverage = subpass.GetElementsCoverage(coverage_clip);
	// The entities don't cover anything. There is nothing to do.
	if (!entities_coverage.has_value()) {
	return std::nullopt;
	}

	// The delegates don't have an opinion on what the entity coverage has to be.
	// Just use that as-is.
	auto delegate_coverage = subpass.delegate_->GetCoverageRect();
	if (!delegate_coverage.has_value()) {
	return entities_coverage;
	}
	// The delegate coverage hint is in given in local space, so apply the subpass
	// transformation.
	delegate_coverage = delegate_coverage->TransformBounds(subpass.xformation_);

	// If the delegate tells us the coverage is smaller than it needs to be, then
	// great. OTOH, if the delegate is being wasteful, limit coverage to what is
	// actually needed.
	return entities_coverage->Intersection(delegate_coverage.value());
	}

	EntityPass* EntityPass::GetSuperpass() const {
	return superpass_;
	}

	EntityPass* EntityPass::AddSubpass(std::unique_ptr<EntityPass> pass) {
	if (!pass) {
	return nullptr;
	}
	FML_DCHECK(pass->superpass_ == nullptr);
	pass->superpass_ = this;

	if (pass->blend_mode_ > Entity::kLastPipelineBlendMode \|\|
	pass->backdrop_filter_proc_.has_value()) {
	reads_from_pass_texture_ += 1;
	}

	auto subpass_pointer = pass.get();
	elements_.emplace_back(std::move(pass));
	return subpass_pointer;
	}

	static RenderTarget CreateRenderTarget(ContentContext& renderer,
	ISize size,
	bool readable) {
	auto context = renderer.GetContext();

	/// All of the load/store actions are managed by `InlinePassContext` when
	/// `RenderPasses` are created, so we just set them to `kDontCare` here.
	/// What's important is the `StorageMode` of the textures, which cannot be
	/// changed for the lifetime of the textures.

	if (context->SupportsOffscreenMSAA()) {
	return RenderTarget::CreateOffscreenMSAA(
	*context, // context
	size, // size
	"EntityPass", // label
	StorageMode::kDeviceTransient, // color_storage_mode
	StorageMode::kDevicePrivate, // color_resolve_storage_mode
	LoadAction::kDontCare, // color_load_action
	StoreAction::kMultisampleResolve, // color_store_action
	readable ? StorageMode::kDevicePrivate
	: StorageMode::kDeviceTransient, // stencil_storage_mode
	LoadAction::kDontCare, // stencil_load_action
	StoreAction::kDontCare // stencil_store_action
	);
	}

	return RenderTarget::CreateOffscreen(
	*context, // context
	size, // size
	"EntityPass", // label
	StorageMode::kDevicePrivate, // color_storage_mode
	LoadAction::kDontCare, // color_load_action
	StoreAction::kDontCare, // color_store_action
	readable ? StorageMode::kDevicePrivate
	: StorageMode::kDeviceTransient, // stencil_storage_mode
	LoadAction::kDontCare, // stencil_load_action
	StoreAction::kDontCare // stencil_store_action
	);
	}

	bool EntityPass::Render(ContentContext& renderer,
	const RenderTarget& render_target) const {
	if (reads_from_pass_texture_ > 0) {
	auto offscreen_target =
	CreateRenderTarget(renderer, render_target.GetRenderTargetSize(), true);
	if (!OnRender(renderer, offscreen_target.GetRenderTargetSize(),
	offscreen_target, Point(), Point(), 0)) {
	return false;
	}

	auto command_buffer = renderer.GetContext()->CreateCommandBuffer();
	command_buffer->SetLabel("EntityPass Root Command Buffer");
	auto render_pass = command_buffer->CreateRenderPass(render_target);
	render_pass->SetLabel("EntityPass Root Render Pass");

	{
	auto size_rect = Rect::MakeSize(offscreen_target.GetRenderTargetSize());
	auto contents = TextureContents::MakeRect(size_rect);
	contents->SetTexture(offscreen_target.GetRenderTargetTexture());
	contents->SetSourceRect(size_rect);

	Entity entity;
	entity.SetContents(contents);
	entity.SetBlendMode(BlendMode::kSource);

	entity.Render(renderer, *render_pass);
	}

	if (!render_pass->EncodeCommands()) {
	return false;
	}
	if (!command_buffer->SubmitCommands()) {
	return false;
	}

	return true;
	}

	return OnRender(renderer, render_target.GetRenderTargetSize(), render_target,
	Point(), Point(), 0);
	}

	EntityPass::EntityResult EntityPass::GetEntityForElement(
	const EntityPass::Element& element,
	ContentContext& renderer,
	InlinePassContext& pass_context,
	ISize root_pass_size,
	Point position,
	uint32_t pass_depth,
	size_t stencil_depth_floor) const {
	Entity element_entity;

	//--------------------------------------------------------------------------
	/// Setup entity element.
	///

	if (const auto& entity = std::get_if<Entity>(&element)) {
	element_entity = *entity;
	if (!position.IsZero()) {
	// If the pass image is going to be rendered with a non-zero position,
	// apply the negative translation to entity copies before rendering them
	// so that they'll end up rendering to the correct on-screen position.
	element_entity.SetTransformation(
	Matrix::MakeTranslation(Vector3(-position)) *
	element_entity.GetTransformation());
	}
	}

	//--------------------------------------------------------------------------
	/// Setup subpass element.
	///

	else if (const auto& subpass_ptr =
	std::get_if<std::unique_ptr<EntityPass>>(&element)) {
	auto subpass = subpass_ptr->get();

	if (subpass->delegate_->CanElide()) {
	return EntityPass::EntityResult::Skip();
	}

	if (subpass->delegate_->CanCollapseIntoParentPass() &&
	!subpass->backdrop_filter_proc_.has_value()) {
	// Directly render into the parent target and move on.
	if (!subpass->OnRender(renderer, root_pass_size,
	pass_context.GetRenderTarget(), position, position,
	stencil_depth_floor)) {
	return EntityPass::EntityResult::Failure();
	}
	return EntityPass::EntityResult::Skip();
	}

	std::shared_ptr<Contents> backdrop_filter_contents = nullptr;
	if (subpass->backdrop_filter_proc_.has_value()) {
	auto texture = pass_context.GetTexture();
	// Render the backdrop texture before any of the pass elements.
	const auto& proc = subpass->backdrop_filter_proc_.value();
	backdrop_filter_contents =
	proc(FilterInput::Make(std::move(texture)), subpass->xformation_);

	// The subpass will need to read from the current pass texture when
	// rendering the backdrop, so if there's an active pass, end it prior to
	// rendering the subpass.
	pass_context.EndPass();
	}

	auto subpass_coverage =
	GetSubpassCoverage(*subpass, Rect::MakeSize(root_pass_size));
	if (subpass->cover_whole_screen_) {
	subpass_coverage = Rect(
	position, Size(pass_context.GetRenderTarget().GetRenderTargetSize()));
	}
	if (backdrop_filter_contents) {
	auto backdrop_coverage = backdrop_filter_contents->GetCoverage(Entity{});
	if (backdrop_coverage.has_value()) {
	backdrop_coverage->origin += position;

	if (subpass_coverage.has_value()) {
	subpass_coverage = subpass_coverage->Union(backdrop_coverage.value());
	} else {
	subpass_coverage = backdrop_coverage;
	}
	}
	}

	if (subpass_coverage.has_value()) {
	subpass_coverage =
	subpass_coverage->Intersection(Rect::MakeSize(root_pass_size));
	}

	if (!subpass_coverage.has_value()) {
	return EntityPass::EntityResult::Skip();
	}

	if (subpass_coverage->size.IsEmpty()) {
	// It is not an error to have an empty subpass. But subpasses that can't
	// create their intermediates must trip errors.
	return EntityPass::EntityResult::Skip();
	}

	RenderTarget subpass_target;
	if (subpass->reads_from_pass_texture_ > 0) {
	subpass_target = CreateRenderTarget(
	renderer, ISize::Ceil(subpass_coverage->size), true);
	} else {
	subpass_target = CreateRenderTarget(
	renderer, ISize::Ceil(subpass_coverage->size), false);
	}

	auto subpass_texture = subpass_target.GetRenderTargetTexture();

	if (!subpass_texture) {
	return EntityPass::EntityResult::Failure();
	}

	auto offscreen_texture_contents =
	subpass->delegate_->CreateContentsForSubpassTarget(
	subpass_texture, subpass->xformation_);

	if (!offscreen_texture_contents) {
	// This is an error because the subpass delegate said the pass couldn't
	// be collapsed into its parent. Yet, when asked how it want's to
	// postprocess the offscreen texture, it couldn't give us an answer.
	//
	// Theoretically, we could collapse the pass now. But that would be
	// wasteful as we already have the offscreen texture and we don't want
	// to discard it without ever using it. Just make the delegate do the
	// right thing.
	return EntityPass::EntityResult::Failure();
	}

	// Stencil textures aren't shared between EntityPasses (as much of the
	// time they are transient).
	if (!subpass->OnRender(renderer, root_pass_size, subpass_target,
	subpass_coverage->origin, position, ++pass_depth,
	subpass->stencil_depth_, backdrop_filter_contents)) {
	return EntityPass::EntityResult::Failure();
	}

	element_entity.SetContents(std::move(offscreen_texture_contents));
	element_entity.SetStencilDepth(subpass->stencil_depth_);
	element_entity.SetBlendMode(subpass->blend_mode_);
	element_entity.SetTransformation(
	Matrix::MakeTranslation(Vector3(subpass_coverage->origin - position)));
	} else {
	FML_UNREACHABLE();
	}

	return EntityPass::EntityResult::Success(element_entity);
	}

	struct StencilLayer {
	std::optional<Rect> coverage;
	size_t stencil_depth;
	};

	bool EntityPass::OnRender(
	ContentContext& renderer,
	ISize root_pass_size,
	const RenderTarget& render_target,
	Point position,
	Point parent_position,
	uint32_t pass_depth,
	size_t stencil_depth_floor,
	std::shared_ptr<Contents> backdrop_filter_contents) const {
	TRACE_EVENT0("impeller", "EntityPass::OnRender");

	auto context = renderer.GetContext();
	InlinePassContext pass_context(context, render_target,
	reads_from_pass_texture_);
	if (!pass_context.IsValid()) {
	return false;
	}

	std::vector<StencilLayer> stencil_stack = {StencilLayer{
	.coverage = Rect::MakeSize(render_target.GetRenderTargetSize()),
	.stencil_depth = stencil_depth_floor}};

	auto render_element = [&stencil_depth_floor, &pass_context, &pass_depth,
	&renderer, &stencil_stack](Entity& element_entity) {
	auto result = pass_context.GetRenderPass(pass_depth);

	if (!result.pass) {
	return false;
	}

	// If the pass context returns a texture, we need to draw it to the current
	// pass. We do this because it's faster and takes significantly less memory
	// than storing/loading large MSAA textures.
	if (result.backdrop_texture) {
	auto size_rect = Rect::MakeSize(result.pass->GetRenderTargetSize());
	auto msaa_backdrop_contents = TextureContents::MakeRect(size_rect);
	msaa_backdrop_contents->SetStencilEnabled(false);
	msaa_backdrop_contents->SetLabel("MSAA backdrop");
	msaa_backdrop_contents->SetSourceRect(size_rect);
	msaa_backdrop_contents->SetTexture(result.backdrop_texture);

	Entity msaa_backdrop_entity;
	msaa_backdrop_entity.SetContents(std::move(msaa_backdrop_contents));
	msaa_backdrop_entity.SetBlendMode(BlendMode::kSource);
	if (!msaa_backdrop_entity.Render(renderer, *result.pass)) {
	return false;
	}
	}

	if (!element_entity.ShouldRender(stencil_stack.back().coverage)) {
	return true; // Nothing to render.
	}

	auto stencil_coverage =
	element_entity.GetStencilCoverage(stencil_stack.back().coverage);

	switch (stencil_coverage.type) {
	case Contents::StencilCoverage::Type::kNone:
	break;
	case Contents::StencilCoverage::Type::kAppend: {
	auto op = stencil_stack.back().coverage;
	stencil_stack.push_back(StencilLayer{
	.coverage = stencil_coverage.coverage,
	.stencil_depth = element_entity.GetStencilDepth() + 1});

	if (!op.has_value()) {
	// Running this append op won't impact the stencil because the whole
	// screen is already being clipped, so skip it.
	return true;
	}
	} break;
	case Contents::StencilCoverage::Type::kRestore: {
	if (stencil_stack.back().stencil_depth <=
	element_entity.GetStencilDepth()) {
	// Drop stencil restores that will do nothing.
	return true;
	}

	FML_DCHECK(stencil_stack.size() > 1);

	stencil_stack.pop_back();

	if (!stencil_stack.back().coverage.has_value()) {
	// Running this restore op won't make anything renderable, so skip it.
	return true;
	}
	} break;
	}

	element_entity.SetStencilDepth(element_entity.GetStencilDepth() -
	stencil_depth_floor);
	if (!element_entity.Render(renderer, *result.pass)) {
	return false;
	}
	return true;
	};

	if (backdrop_filter_proc_.has_value()) {
	if (!backdrop_filter_contents) {
	return false;
	}

	Entity backdrop_entity;
	backdrop_entity.SetContents(std::move(backdrop_filter_contents));
	backdrop_entity.SetTransformation(
	Matrix::MakeTranslation(Vector3(parent_position - position)));
	backdrop_entity.SetStencilDepth(stencil_depth_floor);

	render_element(backdrop_entity);
	}

	for (const auto& element : elements_) {
	EntityResult result =
	GetEntityForElement(element, renderer, pass_context, root_pass_size,
	position, pass_depth, stencil_depth_floor);

	switch (result.status) {
	case EntityResult::kSuccess:
	break;
	case EntityResult::kFailure:
	return false;
	case EntityResult::kSkip:
	continue;
	};

	//--------------------------------------------------------------------------
	/// Setup advanced blends.
	///

	if (result.entity.GetBlendMode() > Entity::kLastPipelineBlendMode) {
	// End the active pass and flush the buffer before rendering "advanced"
	// blends. Advanced blends work by binding the current render target
	// texture as an input ("destination"), blending with a second texture
	// input ("source"), writing the result to an intermediate texture, and
	// finally copying the data from the intermediate texture back to the
	// render target texture. And so all of the commands that have written
	// to the render target texture so far need to execute before it's bound
	// for blending (otherwise the blend pass will end up executing before
	// all the previous commands in the active pass).
	if (!pass_context.EndPass()) {
	return false;
	}

	// Amend an advanced blend filter to the contents, attaching the pass
	// texture.
	auto texture = pass_context.GetTexture();
	if (!texture) {
	return false;
	}

	FilterInput::Vector inputs = {
	FilterInput::Make(result.entity.GetContents()),
	FilterInput::Make(texture,
	result.entity.GetTransformation().Invert())};
	auto contents =
	ColorFilterContents::MakeBlend(result.entity.GetBlendMode(), inputs);
	contents->SetCoverageCrop(result.entity.GetCoverage());
	result.entity.SetContents(std::move(contents));
	result.entity.SetBlendMode(BlendMode::kSource);
	}

	//--------------------------------------------------------------------------
	/// Render the Element.
	///

	if (!render_element(result.entity)) {
	return false;
	}
	}

	return true;
	}

	void EntityPass::IterateAllEntities(
	const std::function<bool(Entity&)>& iterator) {
	if (!iterator) {
	return;
	}

	for (auto& element : elements_) {
	if (auto entity = std::get_if<Entity>(&element)) {
	if (!iterator(*entity)) {
	return;
	}
	continue;
	}
	if (auto subpass = std::get_if<std::unique_ptr<EntityPass>>(&element)) {
	subpass->get()->IterateAllEntities(iterator);
	continue;
	}
	FML_UNREACHABLE();
	}
	}

	std::unique_ptr<EntityPass> EntityPass::Clone() const {
	std::vector<Element> new_elements;
	new_elements.reserve(elements_.size());

	for (const auto& element : elements_) {
	if (auto entity = std::get_if<Entity>(&element)) {
	new_elements.push_back(*entity);
	continue;
	}
	if (auto subpass = std::get_if<std::unique_ptr<EntityPass>>(&element)) {
	new_elements.push_back(subpass->get()->Clone());
	continue;
	}
	FML_UNREACHABLE();
	}

	auto pass = std::make_unique<EntityPass>();
	pass->SetElements(std::move(new_elements));
	return pass;
	}

	void EntityPass::SetTransformation(Matrix xformation) {
	xformation_ = xformation;
	}

	void EntityPass::SetStencilDepth(size_t stencil_depth) {
	stencil_depth_ = stencil_depth;
	}

	void EntityPass::SetBlendMode(BlendMode blend_mode) {
	blend_mode_ = blend_mode;
	cover_whole_screen_ = Entity::BlendModeShouldCoverWholeScreen(blend_mode);
	}

	void EntityPass::SetBackdropFilter(std::optional<BackdropFilterProc> proc) {
	if (superpass_) {
	VALIDATION_LOG << "Backdrop filters cannot be set on EntityPasses that "
	"have already been appended to another pass.";
	}

	backdrop_filter_proc_ = std::move(proc);
	}

	} // namespace impeller