pixmap_image_base.cpp

class SkImmutablePixmap {
public:
    SkImmutablePixmap(const SkImageInfo& info,
                      const void* addr,
                      size_t rowBytes,
                      SkColorTable* ctable = NULL)
        : fPixels(addr), fCTable(ctable), fRowBytes(rowBytes), fInfo(info) {
        SkASSERT((kIndex_8_SkColorType == info.colorType())
                 == (ctable != nullptr));
    }
    virtual ~SkImmutablePixmap() {}
    const void* const         fPixels;
    const SkColorTable* const fCTable;
    const size_t              fRowBytes;
    const SkImageInfo         fInfo;
};

class SkImage_Base : public SkImage {
    // ..............
    virtual SkImmutablePixmap* getPixmap() const;
    // ..............
};

// default implementation
SkImage_Base::SkImmutablePixmap* getPixmap() const {
    SkBitmap bitmap;
    if (!this->getROPixels(&bitmap)) {
        return nullptr;
    }
    SkAutoLockPixels autoLockPixels(bitmap);
    class SkImmutablePixmap_Bitmap : public SkImmutablePixmap {
        SkImmutablePixmap_Bitmap(const SkBitmap& bm)
            : SkImmutablePixmap(bm.info(),
                                bm.getPixels(),
                                bm.rowBytes(),
                                bm.colorTable())
            , fBitmap(bm) {
            SkASSERT(bm.getPixels());  // is locked
            fBitmap.lock(); // hold that lock
        }
        virtual ~SkImmutablePixmap_Bitmap() { fBitmap.unlock(); }
    private:
        SkBitmap fBitmap;
    };
    return new SkImmutablePixmap_Bitmap(bitmap);
}