118 lines
4.2 KiB
C++
118 lines
4.2 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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// 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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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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this->checkForFinish(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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this->checkForFinish(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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* Called after any set of scanlines read/skipped. Updates fCurrScanline,
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* and, if we are at the end, calls onFinish().
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*/
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void checkForFinish(int countLines) {
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fCurrScanline += countLines;
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if (fCurrScanline >= fDstInfo.height()) {
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this->onFinish();
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}
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}
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/**
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* This function will be called after reading/skipping all scanlines to do
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* any necessary cleanups.
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*/
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virtual void onFinish() {} // Default does nothing.
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};
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#endif // SkScanlineDecoder_DEFINED
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