skia2/include/codec/SkCodec.h
scroggo 3a7701c010 Call rewindIfNeeded in SkCodec
Rather than calling it in each subclass, call it once in the base
class. Call it first, since other steps may modify internal structures
which would be replaced by a call to onRewind.

BUG=skia:4284

Review URL: https://codereview.chromium.org/1381483002
2015-09-30 09:15:14 -07:00

482 lines
17 KiB
C++

/*
* Copyright 2015 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef SkCodec_DEFINED
#define SkCodec_DEFINED
#include "../private/SkTemplates.h"
#include "SkColor.h"
#include "SkEncodedFormat.h"
#include "SkImageInfo.h"
#include "SkSize.h"
#include "SkStream.h"
#include "SkTypes.h"
class SkData;
/**
* Abstraction layer directly on top of an image codec.
*/
class SkCodec : SkNoncopyable {
public:
/**
* If this stream represents an encoded image that we know how to decode,
* return an SkCodec that can decode it. Otherwise return NULL.
*
* If NULL is returned, the stream is deleted immediately. Otherwise, the
* SkCodec takes ownership of it, and will delete it when done with it.
*/
static SkCodec* NewFromStream(SkStream*);
/**
* If this data represents an encoded image that we know how to decode,
* return an SkCodec that can decode it. Otherwise return NULL.
*
* Will take a ref if it returns a codec, else will not affect the data.
*/
static SkCodec* NewFromData(SkData*);
virtual ~SkCodec();
/**
* Return the ImageInfo associated with this codec.
*/
const SkImageInfo& getInfo() const { return fSrcInfo; }
/**
* Return a size that approximately supports the desired scale factor.
* The codec may not be able to scale efficiently to the exact scale
* factor requested, so return a size that approximates that scale.
* The returned value is the codec's suggestion for the closest valid
* scale that it can natively support
*/
SkISize getScaledDimensions(float desiredScale) const {
// Negative and zero scales are errors.
SkASSERT(desiredScale > 0.0f);
if (desiredScale <= 0.0f) {
return SkISize::Make(0, 0);
}
// Upscaling is not supported. Return the original size if the client
// requests an upscale.
if (desiredScale >= 1.0f) {
return this->getInfo().dimensions();
}
return this->onGetScaledDimensions(desiredScale);
}
/**
* Return (via desiredSubset) a subset which can decoded from this codec,
* or false if this codec cannot decode subsets or anything similar to
* desiredSubset.
*
* @param desiredSubset In/out parameter. As input, a desired subset of
* the original bounds (as specified by getInfo). If true is returned,
* desiredSubset may have been modified to a subset which is
* supported. Although a particular change may have been made to
* desiredSubset to create something supported, it is possible other
* changes could result in a valid subset.
* If false is returned, desiredSubset's value is undefined.
* @return true if this codec supports decoding desiredSubset (as
* returned, potentially modified)
*/
bool getValidSubset(SkIRect* desiredSubset) const {
return this->onGetValidSubset(desiredSubset);
}
/**
* Format of the encoded data.
*/
SkEncodedFormat getEncodedFormat() const { return this->onGetEncodedFormat(); }
/**
* Used to describe the result of a call to getPixels().
*
* Result is the union of possible results from subclasses.
*/
enum Result {
/**
* General return value for success.
*/
kSuccess,
/**
* The input is incomplete. A partial image was generated.
*/
kIncompleteInput,
/**
* The generator cannot convert to match the request, ignoring
* dimensions.
*/
kInvalidConversion,
/**
* The generator cannot scale to requested size.
*/
kInvalidScale,
/**
* Parameters (besides info) are invalid. e.g. NULL pixels, rowBytes
* too small, etc.
*/
kInvalidParameters,
/**
* The input did not contain a valid image.
*/
kInvalidInput,
/**
* Fulfilling this request requires rewinding the input, which is not
* supported for this input.
*/
kCouldNotRewind,
/**
* startScanlineDecode() was not called before calling getScanlines.
*/
kScanlineDecodingNotStarted,
/**
* This method is not implemented by this codec.
* FIXME: Perhaps this should be kUnsupported?
*/
kUnimplemented,
};
/**
* Whether or not the memory passed to getPixels is zero initialized.
*/
enum ZeroInitialized {
/**
* The memory passed to getPixels is zero initialized. The SkCodec
* may take advantage of this by skipping writing zeroes.
*/
kYes_ZeroInitialized,
/**
* The memory passed to getPixels has not been initialized to zero,
* so the SkCodec must write all zeroes to memory.
*
* This is the default. It will be used if no Options struct is used.
*/
kNo_ZeroInitialized,
};
/**
* Additional options to pass to getPixels.
*/
struct Options {
Options()
: fZeroInitialized(kNo_ZeroInitialized)
, fSubset(NULL)
{}
ZeroInitialized fZeroInitialized;
/**
* If not NULL, represents a subset of the original image to decode.
*
* Must be within the bounds returned by getInfo().
*
* If the EncodedFormat is kWEBP_SkEncodedFormat (the only one which
* currently supports subsets), the top and left values must be even.
*/
SkIRect* fSubset;
};
/**
* Decode into the given pixels, a block of memory of size at
* least (info.fHeight - 1) * rowBytes + (info.fWidth *
* bytesPerPixel)
*
* Repeated calls to this function should give the same results,
* allowing the PixelRef to be immutable.
*
* @param info A description of the format (config, size)
* expected by the caller. This can simply be identical
* to the info returned by getInfo().
*
* This contract also allows the caller to specify
* different output-configs, which the implementation can
* decide to support or not.
*
* A size that does not match getInfo() implies a request
* to scale. If the generator cannot perform this scale,
* it will return kInvalidScale.
*
* If info is kIndex8_SkColorType, then the caller must provide storage for up to 256
* SkPMColor values in ctable. On success the generator must copy N colors into that storage,
* (where N is the logical number of table entries) and set ctableCount to N.
*
* If info is not kIndex8_SkColorType, then the last two parameters may be NULL. If ctableCount
* is not null, it will be set to 0.
*
* If a scanline decode is in progress, scanline mode will end, requiring the client to call
* startScanlineDecode() in order to return to decoding scanlines.
*
* @return Result kSuccess, or another value explaining the type of failure.
*/
Result getPixels(const SkImageInfo& info, void* pixels, size_t rowBytes, const Options*,
SkPMColor ctable[], int* ctableCount);
/**
* Simplified version of getPixels() that asserts that info is NOT kIndex8_SkColorType and
* uses the default Options.
*/
Result getPixels(const SkImageInfo& info, void* pixels, size_t rowBytes);
/**
* Some images may initially report that they have alpha due to the format
* of the encoded data, but then never use any colors which have alpha
* less than 100%. This function can be called *after* decoding to
* determine if such an image truly had alpha. Calling it before decoding
* is undefined.
* FIXME: see skbug.com/3582.
*/
bool reallyHasAlpha() const {
return this->onReallyHasAlpha();
}
/**
* The remaining functions revolve around decoding scanlines.
*/
/**
* Prepare for a scanline decode with the specified options.
*
* After this call, this class will be ready to decode the first scanline.
*
* This must be called in order to call getScanlines or skipScanlines.
*
* This may require rewinding the stream.
*
* Not all SkCodecs support this.
*
* @param dstInfo Info of the destination. If the dimensions do not match
* those of getInfo, this implies a scale.
* @param options Contains decoding options, including if memory is zero
* initialized.
* @param ctable A pointer to a color table. When dstInfo.colorType() is
* kIndex8, this should be non-NULL and have enough storage for 256
* colors. The color table will be populated after decoding the palette.
* @param ctableCount A pointer to the size of the color table. When
* dstInfo.colorType() is kIndex8, this should be non-NULL. It will
* be modified to the true size of the color table (<= 256) after
* decoding the palette.
* @return Enum representing success or reason for failure.
*/
Result startScanlineDecode(const SkImageInfo& dstInfo, const SkCodec::Options* options,
SkPMColor ctable[], int* ctableCount);
/**
* Simplified version of startScanlineDecode() that asserts that info is NOT
* kIndex8_SkColorType and uses the default Options.
*/
Result startScanlineDecode(const SkImageInfo& dstInfo);
/**
* Write the next countLines scanlines into dst.
*
* Not valid to call before calling startScanlineDecode().
*
* @param dst Must be non-null, and large enough to hold countLines
* scanlines of size rowBytes.
* @param countLines Number of lines to write.
* @param rowBytes Number of bytes per row. Must be large enough to hold
* a scanline based on the SkImageInfo used to create this object.
*/
Result getScanlines(void* dst, int countLines, size_t rowBytes);
/**
* Skip count scanlines.
*
* Not valid to call before calling startScanlineDecode().
*
* The default version just calls onGetScanlines and discards the dst.
* NOTE: If skipped lines are the only lines with alpha, this default
* will make reallyHasAlpha return true, when it could have returned
* false.
*/
Result skipScanlines(int countLines);
/**
* The order in which rows are output from the scanline decoder is not the
* same for all variations of all image types. This explains the possible
* output row orderings.
*/
enum SkScanlineOrder {
/*
* By far the most common, this indicates that the image can be decoded
* reliably using the scanline decoder, and that rows will be output in
* the logical order.
*/
kTopDown_SkScanlineOrder,
/*
* This indicates that the scanline decoder reliably outputs rows, but
* they will be returned in reverse order. If the scanline format is
* kBottomUp, the nextScanline() API can be used to determine the actual
* y-coordinate of the next output row, but the client is not forced
* to take advantage of this, given that it's not too tough to keep
* track independently.
*
* For full image decodes, it is safe to get all of the scanlines at
* once, since the decoder will handle inverting the rows as it
* decodes.
*
* For subset decodes and sampling, it is simplest to get and skip
* scanlines one at a time, using the nextScanline() API. It is
* possible to ask for larger chunks at a time, but this should be used
* with caution. As with full image decodes, the decoder will handle
* inverting the requested rows, but rows will still be delivered
* starting from the bottom of the image.
*
* Upside down bmps are an example.
*/
kBottomUp_SkScanlineOrder,
/*
* This indicates that the scanline decoder reliably outputs rows, but
* they will not be in logical order. If the scanline format is
* kOutOfOrder, the nextScanline() API should be used to determine the
* actual y-coordinate of the next output row.
*
* For this scanline ordering, it is advisable to get and skip
* scanlines one at a time.
*
* Interlaced gifs are an example.
*/
kOutOfOrder_SkScanlineOrder,
/*
* Indicates that the entire image must be decoded in order to output
* any amount of scanlines. In this case, it is a REALLY BAD IDEA to
* request scanlines 1-by-1 or in small chunks. The client should
* determine which scanlines are needed and ask for all of them in
* a single call to getScanlines().
*
* Interlaced pngs are an example.
*/
kNone_SkScanlineOrder,
};
/**
* An enum representing the order in which scanlines will be returned by
* the scanline decoder.
*/
SkScanlineOrder getScanlineOrder() const { return this->onGetScanlineOrder(); }
/**
* Returns the y-coordinate of the next row to be returned by the scanline
* decoder. This will be overridden in the case of
* kOutOfOrder_SkScanlineOrder and should be unnecessary in the case of
* kNone_SkScanlineOrder.
*
* Results are undefined when not in scanline decoding mode.
*/
int nextScanline() const {
return this->onNextScanline();
}
protected:
SkCodec(const SkImageInfo&, SkStream*);
virtual SkISize onGetScaledDimensions(float /* desiredScale */) const {
// By default, scaling is not supported.
return this->getInfo().dimensions();
}
virtual SkEncodedFormat onGetEncodedFormat() const = 0;
virtual Result onGetPixels(const SkImageInfo& info,
void* pixels, size_t rowBytes, const Options&,
SkPMColor ctable[], int* ctableCount) = 0;
virtual bool onGetValidSubset(SkIRect* /* desiredSubset */) const {
// By default, subsets are not supported.
return false;
}
virtual bool onReallyHasAlpha() const { return false; }
/**
* If the stream was previously read, attempt to rewind.
*
* If the stream needed to be rewound, call onRewind.
* @returns true if the codec is at the right position and can be used.
* false if there was a failure to rewind.
*
* This is called by getPixels() and start(). Subclasses may call if they
* need to rewind at another time.
*/
bool SK_WARN_UNUSED_RESULT rewindIfNeeded();
/**
* Called by rewindIfNeeded, if the stream needed to be rewound.
*
* Subclasses should do any set up needed after a rewind.
*/
virtual bool onRewind() {
return true;
}
/**
* Get method for the input stream
*/
SkStream* stream() {
return fStream.get();
}
/**
* The remaining functions revolve around decoding scanlines.
*/
/**
* Most images types will be kTopDown and will not need to override this function.
*/
virtual SkScanlineOrder onGetScanlineOrder() const { return kTopDown_SkScanlineOrder; }
/**
* Most images will be kTopDown and will not need to override this function.
*/
virtual int onNextScanline() const { return fCurrScanline; }
/**
* Update the next scanline. Used by interlaced png.
*/
void updateNextScanline(int newY) { fCurrScanline = newY; }
const SkImageInfo& dstInfo() const { return fDstInfo; }
const SkCodec::Options& options() const { return fOptions; }
private:
const SkImageInfo fSrcInfo;
SkAutoTDelete<SkStream> fStream;
bool fNeedsRewind;
// These fields are only meaningful during scanline decodes.
SkImageInfo fDstInfo;
SkCodec::Options fOptions;
int fCurrScanline;
// Methods for scanline decoding.
virtual SkCodec::Result onStartScanlineDecode(const SkImageInfo& dstInfo,
const SkCodec::Options& options, SkPMColor ctable[], int* ctableCount) {
return kUnimplemented;
}
// Naive default version just calls onGetScanlines on temp memory.
virtual SkCodec::Result onSkipScanlines(int countLines) {
SkAutoMalloc storage(fDstInfo.minRowBytes());
// Note that we pass 0 to rowBytes so we continue to use the same memory.
// Also note that while getScanlines checks that rowBytes is big enough,
// onGetScanlines bypasses that check.
// Calling the virtual method also means we do not double count
// countLines.
return this->onGetScanlines(storage.get(), countLines, 0);
}
virtual SkCodec::Result onGetScanlines(void* dst, int countLines,
size_t rowBytes) {
return kUnimplemented;
}
};
#endif // SkCodec_DEFINED