From 070e73868efabc0cdeffd374436efec1ee2c9756 Mon Sep 17 00:00:00 2001
From: Chinmay Garde <chinmaygarde@google.com>
Date: Tue, 1 Jun 2021 14:05:06 -0700
Subject: [PATCH] Patch buffer views.

---
 .../impeller/impeller/compositor/buffer.h     | 24 +++++++++++++++----
 .../impeller/impeller/compositor/buffer.mm    |  3 +++
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/engine/src/flutter/impeller/impeller/compositor/buffer.h b/engine/src/flutter/impeller/impeller/compositor/buffer.h
index 867b9718746..a0987216385 100644
--- a/engine/src/flutter/impeller/impeller/compositor/buffer.h
+++ b/engine/src/flutter/impeller/impeller/compositor/buffer.h
@@ -12,25 +12,39 @@
 
 namespace impeller {
 
+class HostBuffer;
+
 class BufferBase {
  public:
+  ~BufferBase() = default;
+
   virtual uint8_t* GetMapping() const = 0;
 
   virtual size_t GetLength() const = 0;
 };
 
-class BufferView : public BufferBase {
+class BufferView final : public BufferBase {
  public:
-  uint8_t* GetMapping() const {
+  // |BufferBase|
+  ~BufferView() = default;
+
+  // |BufferBase|
+  uint8_t* GetMapping() const override {
     return parent_->GetMapping() + range_in_parent_.offset;
   }
 
-  size_t GetLength() const { return range_in_parent_.length; }
+  // |BufferBase|
+  size_t GetLength() const override { return range_in_parent_.length; }
 
  private:
+  friend HostBuffer;
+
   std::shared_ptr<BufferBase> parent_;
   Range range_in_parent_;
 
+  BufferView(std::shared_ptr<BufferBase> parent, Range range_in_parent)
+      : parent_(std::move(parent)), range_in_parent_(range_in_parent) {}
+
   FML_DISALLOW_COPY_AND_ASSIGN(BufferView);
 };
 
@@ -61,10 +75,12 @@ class HostBuffer : public std::enable_shared_from_this<HostBuffer>,
 
   std::shared_ptr<BufferView> Emplace(size_t length);
 
-  ~HostBuffer();
+  virtual ~HostBuffer();
 
+  // |BufferBase|
   uint8_t* GetMapping() const override { return buffer_; }
 
+  // |BufferBase|
   size_t GetLength() const override { return length_; }
 
   [[nodiscard]] bool Truncate(size_t length);
diff --git a/engine/src/flutter/impeller/impeller/compositor/buffer.mm b/engine/src/flutter/impeller/impeller/compositor/buffer.mm
index 60025aafb19..cb9ba12e05a 100644
--- a/engine/src/flutter/impeller/impeller/compositor/buffer.mm
+++ b/engine/src/flutter/impeller/impeller/compositor/buffer.mm
@@ -27,9 +27,12 @@ HostBuffer::~HostBuffer() {
 }
 
 std::shared_ptr<BufferView> HostBuffer::Emplace(size_t length) {
+  auto old_length = length_;
   if (!Truncate(length_ + length)) {
     return nullptr;
   }
+  return std::shared_ptr<BufferView>(
+      new BufferView(shared_from_this(), Range{old_length, length}));
 }
 
 bool HostBuffer::Truncate(size_t length) {