| /* |
| * 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 SkScanlineDecoder_DEFINED |
| #define SkScanlineDecoder_DEFINED |
| |
| #include "SkTypes.h" |
| #include "SkTemplates.h" |
| #include "SkImageGenerator.h" |
| #include "SkImageInfo.h" |
| |
| class SkScanlineDecoder : public SkNoncopyable { |
| public: |
| // Note for implementations: An SkScanlineDecoder will be deleted by (and |
| // therefore *before*) its associated SkCodec, in case the order matters. |
| virtual ~SkScanlineDecoder() {} |
| |
| /** |
| * Write the next countLines scanlines into dst. |
| * |
| * @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. |
| */ |
| SkImageGenerator::Result getScanlines(void* dst, int countLines, size_t rowBytes) { |
| if ((rowBytes < fDstInfo.minRowBytes() && countLines > 1 ) || countLines <= 0 |
| || fCurrScanline + countLines > fDstInfo.height()) { |
| return SkImageGenerator::kInvalidParameters; |
| } |
| const SkImageGenerator::Result result = this->onGetScanlines(dst, countLines, rowBytes); |
| this->checkForFinish(countLines); |
| return result; |
| } |
| |
| /** |
| * Skip count scanlines. |
| * |
| * 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. |
| */ |
| SkImageGenerator::Result skipScanlines(int countLines) { |
| if (fCurrScanline + countLines > fDstInfo.height()) { |
| // Arguably, we could just skip the scanlines which are remaining, |
| // and return kSuccess. We choose to return invalid so the client |
| // can catch their bug. |
| return SkImageGenerator::kInvalidParameters; |
| } |
| const SkImageGenerator::Result result = this->onSkipScanlines(countLines); |
| this->checkForFinish(countLines); |
| return result; |
| } |
| |
| /** |
| * 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(); |
| } |
| |
| protected: |
| SkScanlineDecoder(const SkImageInfo& requested) |
| : fDstInfo(requested) |
| , fCurrScanline(0) {} |
| |
| virtual bool onReallyHasAlpha() const { return false; } |
| |
| private: |
| const SkImageInfo fDstInfo; |
| int fCurrScanline; |
| |
| // Naive default version just calls onGetScanlines on temp memory. |
| virtual SkImageGenerator::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 SkImageGenerator::Result onGetScanlines(void* dst, int countLines, |
| size_t rowBytes) = 0; |
| |
| /** |
| * Called after any set of scanlines read/skipped. Updates fCurrScanline, |
| * and, if we are at the end, calls onFinish(). |
| */ |
| void checkForFinish(int countLines) { |
| fCurrScanline += countLines; |
| if (fCurrScanline >= fDstInfo.height()) { |
| this->onFinish(); |
| } |
| } |
| |
| /** |
| * This function will be called after reading/skipping all scanlines to do |
| * any necessary cleanups. |
| */ |
| virtual void onFinish() {} // Default does nothing. |
| }; |
| #endif // SkScanlineDecoder_DEFINED |