c0e80c139e
the bottom of the image. In our code before this patch, this would result in cleanup code in onFinish() never being called. We can allow subclasses to take ownership of the SkScanlineDecoder in order to make sure that it is finished/deleted before deleting the decode manager. BUG=skia: Review URL: https://codereview.chromium.org/1212593003
114 lines
4.3 KiB
C++
114 lines
4.3 KiB
C++
/*
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* Copyright 2015 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 SkScanlineDecoder_DEFINED
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#define SkScanlineDecoder_DEFINED
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#include "SkTypes.h"
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#include "SkTemplates.h"
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#include "SkImageGenerator.h"
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#include "SkImageInfo.h"
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class SkScanlineDecoder : public SkNoncopyable {
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public:
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/**
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* Clean up after reading/skipping scanlines.
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*
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* It is possible that not all scanlines will have been read/skipped. In
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* fact, in the case of subset decodes, it is likely that there will be
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* scanlines at the bottom of the image that have been ignored.
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*
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* Note for implementations: An SkScanlineDecoder will be deleted by (and
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* therefore *before*) its associated SkCodec, in case the order matters.
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* However, while the SkCodec base class maintains ownership of the
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* SkScanlineDecoder, the subclass will be deleted before the scanline
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* decoder. If this is an issue, detachScanlineDecoder() provides
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* a means for the subclass to take ownership of the SkScanlineDecoder.
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*/
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virtual ~SkScanlineDecoder() {}
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/**
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* Write the next countLines scanlines into dst.
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*
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* @param dst Must be non-null, and large enough to hold countLines
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* scanlines of size rowBytes.
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* @param countLines Number of lines to write.
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* @param rowBytes Number of bytes per row. Must be large enough to hold
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* a scanline based on the SkImageInfo used to create this object.
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*/
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SkImageGenerator::Result getScanlines(void* dst, int countLines, size_t rowBytes) {
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if ((rowBytes < fDstInfo.minRowBytes() && countLines > 1 ) || countLines <= 0
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|| fCurrScanline + countLines > fDstInfo.height()) {
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return SkImageGenerator::kInvalidParameters;
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}
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const SkImageGenerator::Result result = this->onGetScanlines(dst, countLines, rowBytes);
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fCurrScanline += countLines;
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return result;
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}
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/**
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* Skip count scanlines.
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*
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* The default version just calls onGetScanlines and discards the dst.
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* NOTE: If skipped lines are the only lines with alpha, this default
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* will make reallyHasAlpha return true, when it could have returned
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* false.
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*/
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SkImageGenerator::Result skipScanlines(int countLines) {
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if (fCurrScanline + countLines > fDstInfo.height()) {
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// Arguably, we could just skip the scanlines which are remaining,
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// and return kSuccess. We choose to return invalid so the client
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// can catch their bug.
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return SkImageGenerator::kInvalidParameters;
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}
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const SkImageGenerator::Result result = this->onSkipScanlines(countLines);
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fCurrScanline += countLines;
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return result;
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}
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/**
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* Some images may initially report that they have alpha due to the format
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* of the encoded data, but then never use any colors which have alpha
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* less than 100%. This function can be called *after* decoding to
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* determine if such an image truly had alpha. Calling it before decoding
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* is undefined.
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* FIXME: see skbug.com/3582.
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*/
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bool reallyHasAlpha() const {
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return this->onReallyHasAlpha();
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}
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protected:
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SkScanlineDecoder(const SkImageInfo& requested)
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: fDstInfo(requested)
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, fCurrScanline(0) {}
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virtual bool onReallyHasAlpha() const { return false; }
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const SkImageInfo& dstInfo() const { return fDstInfo; }
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private:
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const SkImageInfo fDstInfo;
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int fCurrScanline;
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// Naive default version just calls onGetScanlines on temp memory.
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virtual SkImageGenerator::Result onSkipScanlines(int countLines) {
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SkAutoMalloc storage(fDstInfo.minRowBytes());
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// Note that we pass 0 to rowBytes so we continue to use the same memory.
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// Also note that while getScanlines checks that rowBytes is big enough,
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// onGetScanlines bypasses that check.
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// Calling the virtual method also means we do not double count
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// countLines.
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return this->onGetScanlines(storage.get(), countLines, 0);
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}
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virtual SkImageGenerator::Result onGetScanlines(void* dst, int countLines,
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size_t rowBytes) = 0;
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};
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#endif // SkScanlineDecoder_DEFINED
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