Eliminate copies of encoded image data

third_party/WebKit/Source/platform/image-decoders/SegmentReader.h

+// Copyright 2016 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 SegmentReader_h
+#define SegmentReader_h
+
+#include "third_party/skia/include/core/SkData.h"
+#include "wtf/Noncopyable.h"
+#include "wtf/PassRefPtr.h"
+#include "wtf/RefCounted.h"
+
+namespace blink {
+
+// Interface that looks like SharedBuffer. Used by ImageDecoders to use various
+// sources of input including:
+// - SharedBuffer
+//   - for when the caller already has a SharedBuffer
+// - SkData
+//   - for when the caller already has an SkData
+// - SkROBuffer
+//   - for when the caller wants to read/write in different threads
+//
+// Unlike SharedBuffer, this is a read-only interface. There is no way to
+// modify the underlying data source.
+class SegmentReader : public RefCounted<SegmentReader> {
+    WTF_MAKE_NONCOPYABLE(SegmentReader);
+public:
+    SegmentReader() {}
+    virtual ~SegmentReader() {}
+    virtual size_t size() const = 0;
+    virtual size_t getSomeData(const char*& data, size_t position) const = 0;

[Peter Kasting, 2016/03/23 02:42:59]

Maybe for clarity at the callers this should take char** instead of char*&?

[scroggo_chromium, 2016/03/24 13:59:46]

I'm not opposed to that in theory, but a goal is to have the same API as
SharedBuffer, which *& matches.

[Peter Kasting, 2016/03/24 22:05:43]

Yeah, that seems sane.  Up to you whether you think this would be worth making a
larger change for, in which case I'd do it separately (although possibly in
advance, so this code can then land in its final form).

[scroggo_chromium, 2016/03/25 01:05:10]

Acknowledged.

+    virtual PassRefPtr<SkData> getAsSkData() const = 0;
+};
+
+} // namespace blink
+#endif // SegmentReader_h