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