/*
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* Copyright 2016 Google Inc.
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#ifndef SkStreamBuffer_DEFINED
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#define SkStreamBuffer_DEFINED
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#include "SkData.h"
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#include "SkStream.h"
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#include "SkTypes.h"
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#include "../private/SkTHash.h"
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/**
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* Helper class for reading from a stream that may not have all its data
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* available yet.
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*
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* Used by GIFImageReader, and currently set up for that use case.
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*
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* Buffers up to 256 * 3 bytes (256 colors, with 3 bytes each) to support GIF.
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* FIXME (scroggo): Make this more general purpose?
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*/
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class SkStreamBuffer : SkNoncopyable {
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public:
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SkStreamBuffer(std::unique_ptr<SkStream>);
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~SkStreamBuffer();
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/**
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* Return a pointer the buffered data.
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*
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* The number of bytes buffered is the number passed to buffer()
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* after the last call to flush().
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*/
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const char* get() const;
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/**
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* Buffer from the stream into our buffer.
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*
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* If this call returns true, get() can be used to access |bytes| bytes
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* from the stream. In addition, markPosition() can be called to mark this
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* position and enable calling getAtPosition() later to retrieve |bytes|
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* bytes.
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*
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* @param bytes Total number of bytes desired.
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*
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* @return Whether all bytes were successfully buffered.
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*/
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bool buffer(size_t bytes);
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/**
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* Flush the buffer.
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*
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* After this call, no bytes are buffered.
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*/
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void flush() {
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if (fHasLengthAndPosition) {
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if (fTrulyBuffered < fBytesBuffered) {
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fStream->move(fBytesBuffered - fTrulyBuffered);
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}
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fTrulyBuffered = 0;
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}
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fPosition += fBytesBuffered;
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fBytesBuffered = 0;
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}
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/**
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* Mark the current position in the stream to return to it later.
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*
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* This is the position of the start of the buffer. After this call, a
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* a client can call getDataAtPosition to retrieve all the bytes currently
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* buffered.
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*
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* @return size_t Position which can be passed to getDataAtPosition later
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* to retrieve the data currently buffered.
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*/
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size_t markPosition();
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/**
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* Retrieve data at position, as previously marked by markPosition().
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*
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* @param position Position to retrieve data, as marked by markPosition().
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* @param length Amount of data required at position.
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* @return SkData The data at position.
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*/
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sk_sp<SkData> getDataAtPosition(size_t position, size_t length);
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private:
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static constexpr size_t kMaxSize = 256 * 3;
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std::unique_ptr<SkStream> fStream;
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size_t fPosition;
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char fBuffer[kMaxSize];
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size_t fBytesBuffered;
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// If the stream has a length and position, we can make two optimizations:
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// - We can skip buffering
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// - During parsing, we can store the position and size of data that is
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// needed later during decoding.
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const bool fHasLengthAndPosition;
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// When fHasLengthAndPosition is true, we do not need to actually buffer
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// inside buffer(). We'll buffer inside get(). This keeps track of how many
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// bytes we've buffered inside get(), for the (non-existent) case of:
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// buffer(n)
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// get()
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// buffer(n + u)
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// get()
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// The second call to get() needs to only truly buffer the part that was
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// not already buffered.
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mutable size_t fTrulyBuffered;
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// Only used if !fHasLengthAndPosition. In that case, markPosition will
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// copy into an SkData, stored here.
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SkTHashMap<size_t, SkData*> fMarkedData;
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};
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#endif // SkStreamBuffer_DEFINED
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