components: Add Exosphere component.

components/exo/shared_memory.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COMPONENTS_EXO_SHARED_MEMORY_H_
+#define COMPONENTS_EXO_SHARED_MEMORY_H_
+
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/shared_memory.h"
+#include "components/exo/exo_export.h"
+#include "ui/gfx/buffer_types.h"
+#include "ui/gfx/geometry/size.h"
+
+namespace exo {
+class Buffer;
+
+// Shared memory abstraction. Provides a wrapper around base::SharedMemory
+// with functionality to create buffers from the memory to use for display.
+class EXO_EXPORT SharedMemory {
+ public:
+  explicit SharedMemory(const base::SharedMemoryHandle& handle);
+  ~SharedMemory();
+
+  // Creates a buffer from the shared memory. The buffer is created offset bytes
+  // into the memory and has width and height as specified. The stride
+  // arguments specifies the number of bytes from beginning of one row to the
+  // beginning of the next. The format is the pixel format of the buffer and
+  // must be one of RGBX_8888, RGBA_8888, BGRX_8888, BGRA_8888.
+  scoped_ptr<Buffer> CreateBuffer(const gfx::Size& size,
+                                  gfx::BufferFormat format,
+                                  unsigned offset,
+                                  int stride);

[lpique, 2015/11/11 19:22:07]

It's a bit inconsistent that offset is unsigned and stride is not.

[reveman, 2015/11/11 19:45:19]

Negative stride is a valid use-case even though we don't support that yet. it
can be used to flip the scanline order of a buffer from top-down to bottom-up.
Most of the buffer related code in chromium support negative stride and we might
want the implementation of this function support that in the future. The lack of
support here is an implementation detail and I prefer to not expose that in the
API.

+
+ private:
+  base::SharedMemory shared_memory_;
+
+  DISALLOW_COPY_AND_ASSIGN(SharedMemory);
+};
+
+}  // namespace exo
+
+#endif  // COMPONENTS_EXO_SHARED_MEMORY_H_