[RK3288][Android6.0] Skia中的编解码小结

Platform: Rockchip
OS: Android 6.0
Kernel: 3.10.92

编解码器注册：

SKIA的编解码部分通过一个模板类来实现，这样做的为了实现不同类型的codec兼容
external\skia\include\core\SkTRegistry.h

template <typename T> class SkTRegistry : SkNoncopyable {
public:typedef T Factory;//fFact即传进去来的fact类型，其实它是一个函数指针，后面创建codec会调用。explicit SkTRegistry(T fact) : fFact(fact) {
#ifdef SK_BUILD_FOR_ANDROID// work-around for double-initialization bug{//gHead是链表头SkTRegistry* reg = gHead;//循环比较每个元素while (reg) {//找到就返回if (reg == this) {return;}//比较下一个reg = reg->fChain;}}
#endif//没有找到则说明是没注册过fChain = gHead;//当前最新注册作为表头gHead  = this;}static const SkTRegistry* Head() { return gHead; }const SkTRegistry* next() const { return fChain; }const Factory& factory() const { return fFact; }
};

模板类被定义成如下type:
SkImageDecoder.h

typedef SkTRegistry<SkImageDecoder*(*)(SkStreamRewindable*)>        SkImageDecoder_DecodeReg;
typedef SkTRegistry<SkImageDecoder::Format(*)(SkStreamRewindable*)> SkImageDecoder_FormatReg;

SkImageEncoder.h

typedef SkTRegistry<SkImageEncoder*(*)(SkImageEncoder::Type)> SkImageEncoder_EncodeReg;

调用例子，比如jpeg编解码模块的使用：
SkImageDecoder_libjpeg.cpp

static SkImageDecoder_DecodeReg gDReg(sk_libjpeg_dfactory);
static SkImageEncoder_EncodeReg gEReg(sk_libjpeg_efactory);

参数factory这样就被注册到末班的链表中了，供后面创建调用。

创建：

只看解码部分
SkImageDecoder_FactoryRegistrar.cpp

SkImageDecoder* image_decoder_from_stream(SkStreamRewindable* stream) {SkImageDecoder* codec = NULL;//取出链表头const SkImageDecoder_DecodeReg* curr = SkImageDecoder_DecodeReg::Head();//循环调用每个解码器while (curr) {//获取的是fFact，而我们的factory实现就是赋值给它的//根据stream来判断能否找到对应的codeccodec = curr->factory()(stream);//找到就返回if (codec) {return codec;}//不适合就继续看下一个codec是否符合curr = curr->next();}return NULL;
}

继续拿jpeg当调用例子，curr->factory()对应的就是sk_libjpeg_dfactory()，
SkImageDecoder_libjpeg.cpp

static SkImageDecoder* sk_libjpeg_dfactory(SkStreamRewindable* stream) {//先判断stream是不是jpeg流if (is_jpeg(stream)) {//SkNEW其实就是new的实现return SkNEW(SkJPEGImageDecoder);}return NULL;
}

这样其实就是创建了类SkJPEGImageDecoder

编解码

编解码部分必须要子类实现：
SkImageDecoder.h

    // must be overridden in subclasses. This guy is called by decode(...)virtual bool onDecode(SkStream*, SkBitmap* bitmap, Mode) = 0;

还是拿JPEG为例

bool SkJPEGImageDecoder::onDecode(SkStream* stream, SkBitmap* bm, Mode mode){#ifdef USE_HW_JPEGSkStream *thumbStream = NULL;SkJpegVPUMemStream *vpuStream = NULL;ReusePmem thumbPmem; //if hw decode thumbnail, reuse the thumb data in pmem, do not malloc vmthumbPmem.reuse = 0;AutoScaleBitmap thumbBitmap;HW_DEBUG("JPEG HW Decode!");
do{
......if (SkImageDecoder::kDecodeBounds_Mode != mode) {//use hardvpu mem sometimes when it is not decodeBounds_Modebool markSupport = stream->markSupport();markSupport = true;HW_DEBUG("markSupport: %d", markSupport);if(markSupport){//only markSupport and not justcalwh
#ifdef WH_DEBUG_JPEGAutoTimeMillis atm("JPEG read stream.");
#endif//should change to mark a new value for stream?vpuStream = new SkJpegVPUMemStream(stream, &streamlen);if(vpuStream->getLength() <= 0){HW_DEBUG("VPU STREAM LENGTH less than ZERO!");break;}stream = vpuStream;} else {HW_DEBUG("===========goto jpeg soft decode,need to debug=======");goto __SOFT_DEC;}}HwJpegInputInfo hwInfo;HwJpegOutputInfo outInfo;hwInfo.justcaloutwh = SkImageDecoder::kDecodeBounds_Mode != mode? 0:1;outInfo.thumbPmem = &thumbPmem;int pixelBytes = -1;sk_hw_jpeg_source_mgr sk_hw_stream(stream,this,&hwInfo,vpuStream != NULL);hwInfo.streamCtl.inStream = &sk_hw_stream;hwInfo.streamCtl.wholeStreamLength = streamlen;// > 64M? break;HW_DEBUG("Stream length: %d", hwInfo.streamCtl.wholeStreamLength);hwInfo.streamCtl.thumbOffset = -1;hwInfo.streamCtl.thumbLength = -1;hwInfo.streamCtl.useThumb = 0;PostProcessInfo * ppInfo = &hwInfo.ppInfo;
......if(hw_jpeg_decode(&hwInfo,&outInfo, &reuseBitmap, bm->width(), bm->height()) >= 0){if(reuseBitmap < 0){HW_DEBUG("REUSE BITMAP FAILED.");if(vpuStream != NULL){delete vpuStream;}return false;}
......}
}while(0);
#endif
__SOFT_DEC:
......int status = jpeg_read_header(&cinfo, true);if (status != JPEG_HEADER_OK) {#ifdef USE_HW_JPEGRELEASE_STREAM;#endifreturn return_false(cinfo, *bm, "read_header");}......if (!jpeg_start_decompress(&cinfo)) {
......#ifdef USE_HW_JPEGRELEASE_STREAM;#endifreturn tmp;} else {#ifdef USE_HW_JPEGRELEASE_STREAM;#endifreturn return_false(cinfo, *bm, "start_decompress");}}sampleSize = recompute_sampleSize(sampleSize, cinfo);......jpeg_finish_decompress(&cinfo);#ifdef USE_HW_JPEGRELEASE_STREAM;#endifreturn true;}

虽然次函数对soft/hard decode都有做实现，但是发现写死了(stream->markSupport()直接返回false)是soft decoder，不明白是什么原因。

参考：

Android图片编解码实现方案（Skia） demo

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[RK3288][Android6.0] Skia中的编解码小结

编解码器注册：

创建：

编解码

参考：

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