[Impeller] Updated TextureSourceVK docs and deleted unused ivars

impeller/renderer/backend/vulkan/swapchain_impl_vk.cc

@@ -435,7 +435,7 @@ bool SwapchainImplVK::Present(const std::shared_ptr<SwapchainImageVK>& image,
     barrier.dst_access = {};
     barrier.dst_stage = vk::PipelineStageFlagBits::eBottomOfPipe;
 
-    if (!image->SetLayout(barrier)) {
+    if (!image->SetLayout(barrier).ok()) {
       return false;
     }
 

impeller/renderer/backend/vulkan/texture_source_vk.cc

@@ -27,10 +27,10 @@ vk::ImageLayout TextureSourceVK::SetLayoutWithoutEncoding(
   return old_layout;
 }
 
-bool TextureSourceVK::SetLayout(const BarrierVK& barrier) const {
+fml::Status TextureSourceVK::SetLayout(const BarrierVK& barrier) const {
   const auto old_layout = SetLayoutWithoutEncoding(barrier.new_layout);
   if (barrier.new_layout == old_layout) {
-    return true;
+    return {};
   }
 
   vk::ImageMemoryBarrier image_barrier;
@@ -55,7 +55,7 @@ bool TextureSourceVK::SetLayout(const BarrierVK& barrier) const {
                                      image_barrier       // image barriers
   );
 
-  return true;
+  return {};
 }
 
 }  // namespace impeller

impeller/renderer/backend/vulkan/texture_source_vk.h

@@ -5,6 +5,7 @@
 #pragma once
 
 #include "flutter/fml/macros.h"
+#include "flutter/fml/status.h"
 #include "impeller/base/thread.h"
 #include "impeller/core/texture_descriptor.h"
 #include "impeller/renderer/backend/vulkan/barrier_vk.h"
@@ -13,6 +14,10 @@
 
 namespace impeller {
 
+/// Abstract base class that represents a vkImage and an vkImageView.
+///
+/// This is intended to be used with an impeller::TextureVK. Example
+/// implementations represent swapchain images or uploaded textures.
 class TextureSourceVK {
  public:
   virtual ~TextureSourceVK();
@@ -23,10 +28,26 @@ class TextureSourceVK {
 
   virtual vk::ImageView GetImageView() const = 0;
 
-  bool SetLayout(const BarrierVK& barrier) const;
+  /// Encodes the layout transition `barrier` to `barrier.cmd_buffer` for the
+  /// image.
+  ///
+  /// The transition is from the layout stored via `SetLayoutWithoutEncoding` to
+  /// `barrier.new_layout`.
+  fml::Status SetLayout(const BarrierVK& barrier) const;
 
+  /// Store the layout of the image.
+  ///
+  /// This just is bookkeeping on the CPU, to actually set the layout use
+  /// `SetLayout`.
+  ///
+  /// @param layout The new layout.
+  /// @return The old layout.
   vk::ImageLayout SetLayoutWithoutEncoding(vk::ImageLayout layout) const;
 
+  /// Get the last layout assigned to the TextureSourceVK.
+  ///
+  /// This value is synchronized with the GPU via SetLayout so it may not
+  /// reflect the actual layout.
   vk::ImageLayout GetLayout() const;
 
  protected:

impeller/renderer/backend/vulkan/texture_vk.cc

@@ -137,7 +137,7 @@ std::shared_ptr<const TextureSourceVK> TextureVK::GetTextureSource() const {
 }
 
 bool TextureVK::SetLayout(const BarrierVK& barrier) const {
-  return source_ ? source_->SetLayout(barrier) : false;
+  return source_ ? source_->SetLayout(barrier).ok() : false;
 }
 
 vk::ImageLayout TextureVK::SetLayoutWithoutEncoding(

impeller/renderer/backend/vulkan/texture_vk.h

@@ -40,9 +40,6 @@ class TextureVK final : public Texture, public BackendCast<TextureVK, Texture> {
  private:
   std::weak_ptr<Context> context_;
   std::shared_ptr<TextureSourceVK> source_;
-  mutable RWMutex layout_mutex_;
-  mutable vk::ImageLayout layout_ IPLR_GUARDED_BY(layout_mutex_) =
-      vk::ImageLayout::eUndefined;
 
   // |Texture|
   void SetLabel(std::string_view label) override;