skia___skbitmap___理解

刚开始做，一点一点增加吧， 其实不是很难，关键是他在不同的图像配置参数下 如何分配内存的，

#include "Sk64.h"

#include "SkColor.h"
#include "SkPoint.h"
#include "SkRefCnt.h"


struct SkIRect;
class SkColorTable;
class SkPaint;
class SkPixelRef;
class SkRegion;
class SkFlattenableReadBuffer;
class SkFlattenableWriteBuffer;


/** \class SkBitmap


    The SkBitmap class specifies a raster bitmap. A bitmap has an integer width
    and height, and a format (config), and a pointer to the actual pixels.
    Bitmaps can be drawn into a SkCanvas, but they are also used to specify the target
    of a SkCanvas' drawing operations.
*/
class SkBitmap {
public:
    class Allocator;


    enum Config {
        kNo_Config,         //!< bitmap has not been configured
        kA1_Config,         //!< 1-bit per pixel, (0 is transparent, 1 is opaque)
        kA8_Config,         //!< 8-bits per pixel, with only alpha specified (0 is transparent, 0xFF is opaque)
        kIndex8_Config,     //!< 8-bits per pixel, using SkColorTable to specify the colors
        kRGB_565_Config,    //!< 16-bits per pixel, (see SkColorPriv.h for packing)
        kARGB_4444_Config,  //!< 16-bits per pixel, (see SkColorPriv.h for packing)
        kARGB_8888_Config,  //!< 32-bits per pixel, (see SkColorPriv.h for packing)
        kRLE_Index8_Config,


        kConfigCount
    };


    /** Default construct creates a bitmap with zero width and height, and no pixels.
        Its config is set to kNo_Config.
    */
    SkBitmap();
    /** Constructor initializes the new bitmap by copying the src bitmap. All fields are copied,
        but ownership of the pixels remains with the src bitmap.
    */
    SkBitmap(const SkBitmap& src);
    /** Decrements our (shared) pixel ownership if needed.
    */
    ~SkBitmap();


    /** Copies the src bitmap into this bitmap. Ownership of the src bitmap's pixels remains
        with the src bitmap.
    */
    SkBitmap& operator=(const SkBitmap& src);
    /** Swap the fields of the two bitmaps. This routine is guaranteed to never fail or throw.
    */
    //  This method is not exported to java.
    void swap(SkBitmap& other);


    /** Return true iff the bitmap has empty dimensions.
    */
    bool empty() const { return 0 == fWidth || 0 == fHeight; }


    /** Return true iff the bitmap has no pixels nor a pixelref. Note: this can
        return true even if the dimensions of the bitmap are > 0 (see empty()).
    */
    bool isNull() const { return NULL == fPixels && NULL == fPixelRef; }


    /** Return the config for the bitmap.
    */
    Config  config() const { return (Config)fConfig; }
    /** DEPRECATED, use config()
    */
    Config  getConfig() const { return this->config(); }
    /** Return the bitmap's width, in pixels.
    */
    int width() const { return fWidth; }
    /** Return the bitmap's height, in pixels.
    */
    int height() const { return fHeight; }
    /** Return the number of bytes between subsequent rows of the bitmap.
    */
    int rowBytes() const { return fRowBytes; }


    /** Return the shift amount per pixel (i.e. 0 for 1-byte per pixel, 1 for
        2-bytes per pixel configs, 2 for 4-bytes per pixel configs). Return 0
        for configs that are not at least 1-byte per pixel (e.g. kA1_Config
        or kNo_Config)
    */
    int shiftPerPixel() const { return fBytesPerPixel >> 1; }


    /** Return the number of bytes per pixel based on the config. If the config
        does not have at least 1 byte per (e.g. kA1_Config) then 0 is returned.
    */
    int bytesPerPixel() const { return fBytesPerPixel; }


    /** Return the rowbytes expressed as a number of pixels (like width and
        height). Note, for 1-byte per pixel configs like kA8_Config, this will
        return the same as rowBytes(). Is undefined for configs that are less
        than 1-byte per pixel (e.g. kA1_Config)
    */
    int rowBytesAsPixels() const { return fRowBytes >> (fBytesPerPixel >> 1); }


    /** Return the address of the pixels for this SkBitmap.
    */
    void* getPixels() const { return fPixels; }


    /** Return the byte size of the pixels, based on the height and rowBytes.
        Note this truncates the result to 32bits. Call getSize64() to detect
        if the real size exceeds 32bits.
    */
    size_t getSize() const { return fHeight * fRowBytes; }


    /** Return the byte size of the pixels, based on the height and rowBytes.
        This routine is slightly slower than getSize(), but does not truncate
        the answer to 32bits.
    */
    Sk64 getSize64() const {
        Sk64 size;
        size.setMul(fHeight, fRowBytes);
        return size;
    }


    /** Returns true if the bitmap is opaque (has no translucent/transparent pixels).
    */
    bool isOpaque() const;
    /** Specify if this bitmap's pixels are all opaque or not. Is only meaningful for configs
        that support per-pixel alpha (RGB32, A1, A8).
    */
    void setIsOpaque(bool);  ///设置是否透明只是在per-pixel alpha (RGB32, A1, A8)时支持


    /** Reset the bitmap to its initial state (see default constructor). If we are a (shared)
        owner of the pixels, that ownership is decremented.
    */
    void reset();


    /** Given a config and a width, this computes the optimal rowBytes value. This is called automatically
        if you pass 0 for rowBytes to setConfig().
    */
    static int ComputeRowBytes(Config c, int width);


    /** Return the bytes-per-pixel for the specified config. If the config is
        not at least 1-byte per pixel, return 0, including for kNo_Config.
    */
    static int ComputeBytesPerPixel(Config c);


    /** Return the shift-per-pixel for the specified config. If the config is
     not at least 1-byte per pixel, return 0, including for kNo_Config.
     */
    static int ComputeShiftPerPixel(Config c) {
        return ComputeBytesPerPixel(c) >> 1;
    }


    static Sk64 ComputeSize64(Config, int width, int height);
    static size_t ComputeSize(Config, int width, int height);


    /** Set the bitmap's config and dimensions. If rowBytes is 0, then
        ComputeRowBytes() is called to compute the optimal value. This resets
        any pixel/colortable ownership, just like reset().
    */
    void setConfig(Config, int width, int height, int rowBytes = 0);
    /** Use this to assign a new pixel address for an existing bitmap. This
        will automatically release any pixelref previously installed. Only call
        this if you are handling ownership/lifetime of the pixel memory.


        If the bitmap retains a reference to the colortable (assuming it is
        not null) it will take care of incrementing the reference count.


        @param pixels   Address for the pixels, managed by the caller.
        @param ctable   ColorTable (or null) that matches the specified pixels
    */
    void setPixels(void* p, SkColorTable* ctable = NULL);


    /** Use the standard HeapAllocator to create the pixelref that manages the
        pixel memory. It will be sized based on the current width/height/config.
        If this is called multiple times, a new pixelref object will be created
        each time.


        If the bitmap retains a reference to the colortable (assuming it is
        not null) it will take care of incrementing the reference count.


        @param ctable   ColorTable (or null) to use with the pixels that will
                        be allocated. Only used if config == Index8_Config
        @return true if the allocation succeeds. If not the pixelref field of
                     the bitmap will be unchanged.
    */
    bool allocPixels(SkColorTable* ctable = NULL) {
        return this->allocPixels(NULL, ctable);
    }


    /** Use the specified Allocator to create the pixelref that manages the
        pixel memory. It will be sized based on the current width/height/config.
        If this is called multiple times, a new pixelref object will be created
        each time.


        If the bitmap retains a reference to the colortable (assuming it is
        not null) it will take care of incrementing the reference count.


        @param allocator The Allocator to use to create a pixelref that can
                         manage the pixel memory for the current
                         width/height/config. If allocator is NULL, the standard
                         HeapAllocator will be used.
        @param ctable   ColorTable (or null) to use with the pixels that will
                        be allocated. Only used if config == Index8_Config.
                        If it is non-null and the config is not Index8, it will
                        be ignored.
        @return true if the allocation succeeds. If not the pixelref field of
                     the bitmap will be unchanged.
    */
    bool allocPixels(Allocator* allocator, SkColorTable* ctable);


    /** Return the current pixelref object, of any
    */
    SkPixelRef* pixelRef() const { return fPixelRef; }
    /** Return the offset into the pixelref, if any. Will return 0 if there is
        no pixelref installed.
    */
    size_t pixelRefOffset() const { return fPixelRefOffset; }
    /** Assign a pixelref and optional offset. Pixelrefs are reference counted,
        so the existing one (if any) will be unref'd and the new one will be
        ref'd.
    */
    SkPixelRef* setPixelRef(SkPixelRef* pr, size_t offset = 0);


    /** Call this to ensure that the bitmap points to the current pixel address
        in the pixelref. Balance it with a call to unlockPixels(). These calls
        are harmless if there is no pixelref.
    */
    void lockPixels() const;
    /** When you are finished access the pixel memory, call this to balance a
        previous call to lockPixels(). This allows pixelrefs that implement
        cached/deferred image decoding to know when there are active clients of
        a given image.
    */
    void unlockPixels() const;


    /** Call this to be sure that the bitmap is valid enough to be drawn (i.e.
        it has non-null pixels, and if required by its config, it has a
        non-null colortable. Returns true if all of the above are met.
    */
    bool readyToDraw() const {
        return this->getPixels() != NULL &&
               ((this->config() != kIndex8_Config && this->config() != kRLE_Index8_Config) ||
                       fColorTable != NULL);
    }


    /** Return the bitmap's colortable (if any). Does not affect the colortable's
        reference count.
    */
    SkColorTable* getColorTable() const { return fColorTable; }   ///获取颜色表


    /** Returns a non-zero, unique value corresponding to the pixels in our
        pixelref, or 0 if we do not have a pixelref. Each time the pixels are
        changed (and notifyPixelsChanged is called), a different generation ID
        will be returned.
    */
    uint32_t getGenerationID() const;


    /** Call this if you have changed the contents of the pixels. This will in-
        turn cause a different generation ID value to be returned from
        getGenerationID().
    */
    void notifyPixelsChanged() const;


    /** Initialize the bitmap's pixels with the specified color+alpha, automatically converting into the correct format
        for the bitmap's config. If the config is kRGB_565_Config, then the alpha value is ignored.
        If the config is kA8_Config, then the r,g,b parameters are ignored.
    */
    void eraseARGB(U8CPU a, U8CPU r, U8CPU g, U8CPU b) const;
    /** Initialize the bitmap's pixels with the specified color+alpha, automatically converting into the correct format
        for the bitmap's config. If the config is kRGB_565_Config, then the alpha value is presumed
        to be 0xFF. If the config is kA8_Config, then the r,g,b parameters are ignored and the
        pixels are all set to 0xFF.
    */
    void eraseRGB(U8CPU r, U8CPU g, U8CPU b) const {
        this->eraseARGB(0xFF, r, g, b);
    }
    /** Initialize the bitmap's pixels with the specified color, automatically converting into the correct format
        for the bitmap's config. If the config is kRGB_565_Config, then the color's alpha value is presumed
        to be 0xFF. If the config is kA8_Config, then only the color's alpha value is used.
    */
    void eraseColor(SkColor c) const {
        this->eraseARGB(SkColorGetA(c), SkColorGetR(c), SkColorGetG(c),
                        SkColorGetB(c));
    }


    /** Scroll (a subset of) the contents of this bitmap by dx/dy. If there are
        no pixels allocated (i.e. getPixels() returns null) the method will
        still update the inval region (if present).


        @param subset The subset of the bitmap to scroll/move. To scroll the
                      entire contents, specify [0, 0, width, height] or just
                      pass null.
        @param dx The amount to scroll in X
        @param dy The amount to scroll in Y
        @param inval Optional (may be null). Returns the area of the bitmap that
                     was scrolled away. E.g. if dx = dy = 0, then inval would
                     be set to empty. If dx >= width or dy >= height, then
                     inval would be set to the entire bounds of the bitmap.
        @return true if the scroll was doable. Will return false if the bitmap
                     uses an unsupported config for scrolling (only kA8,
                     kIndex8, kRGB_565, kARGB_4444, kARGB_8888 are supported).
                     If no pixels are present (i.e. getPixels() returns false)
                     inval will still be updated, and true will be returned.
    */
    bool scrollRect(const SkIRect* subset, int dx, int dy,
                    SkRegion* inval = NULL) const;


    /** Returns the address of the specified pixel. This performs a runtime
        check to know the size of the pixels, and will return the same answer
        as the corresponding size-specific method (e.g. getAddr16). Since the
        check happens at runtime, it is much slower than using a size-specific
        version. Unlike the size-specific methods, this routine also checks if
        getPixels() returns null, and returns that. The size-specific routines
        perform a debugging assert that getPixels() is not null, but they do
        not do any runtime checks.
    */
    void* getAddr(int x, int y) const;


    /** Returns the address of the pixel specified by x,y for 32bit pixels.
    */
    inline uint32_t* getAddr32(int x, int y) const;
    /** Returns the address of the pixel specified by x,y for 16bit pixels.
    */
    inline uint16_t* getAddr16(int x, int y) const;
    /** Returns the address of the pixel specified by x,y for 8bit pixels.
    */
    inline uint8_t* getAddr8(int x, int y) const;
    /** Returns the address of the byte containing the pixel specified by x,y
        for 1bit pixels.
        */
    inline uint8_t* getAddr1(int x, int y) const;


    /** Returns the color corresponding to the pixel specified by x,y for
        colortable based bitmaps.
    */
    inline SkPMColor getIndex8Color(int x, int y) const;


    /** Set dst to be a setset of this bitmap. If possible, it will share the
        pixel memory, and just point into a subset of it. However, if the config
        does not support this, a local copy will be made and associated with
        the dst bitmap. If the subset rectangle, intersected with the bitmap's
        dimensions is empty, or if there is an unsupported config, false will be
        returned and dst will be untouched.
        @param dst  The bitmap that will be set to a subset of this bitmap
        @param subset The rectangle of pixels in this bitmap that dst will
                      reference.
        @return true if the subset copy was successfully made.
    */
    bool extractSubset(SkBitmap* dst, const SkIRect& subset) const;


    /** Makes a deep copy of this bitmap, respecting the requested config.
        Returns false if either there is an error (i.e. the src does not have
        pixels) or the request cannot be satisfied (e.g. the src has per-pixel
        alpha, and the requested config does not support alpha).
        @param dst The bitmap to be sized and allocated
        @param c The desired config for dst
        @param allocator Allocator used to allocate the pixelref for the dst
                         bitmap. If this is null, the standard HeapAllocator
                         will be used.
        @return true if the copy could be made.
    */
    bool copyTo(SkBitmap* dst, Config c, Allocator* allocator = NULL) const;


    /** Returns true if this bitmap can be deep copied into the requested config
        by calling copyTo().
     */
    bool canCopyTo(Config newConfig) const;


    bool hasMipMap() const;
    void buildMipMap(bool forceRebuild = false);
    void freeMipMap();


    /** Given scale factors sx, sy, determine the miplevel available in the
        bitmap, and return it (this is the amount to shift matrix iterators
        by). If dst is not null, it is set to the correct level.
    */
    int extractMipLevel(SkBitmap* dst, SkFixed sx, SkFixed sy);


    void extractAlpha(SkBitmap* dst) const {
        this->extractAlpha(dst, NULL, NULL);
    }


    void extractAlpha(SkBitmap* dst, const SkPaint* paint,
                      SkIPoint* offset) const;


    void flatten(SkFlattenableWriteBuffer&) const;
    void unflatten(SkFlattenableReadBuffer&);


    SkDEBUGCODE(void validate() const;)


    class Allocator : public SkRefCnt {
    public:
        /** Allocate the pixel memory for the bitmap, given its dimensions and
            config. Return true on success, where success means either setPixels
            or setPixelRef was called. The pixels need not be locked when this
            returns. If the config requires a colortable, it also must be
            installed via setColorTable. If false is returned, the bitmap and
            colortable should be left unchanged.
        */
        virtual bool allocPixelRef(SkBitmap*, SkColorTable*) = 0;
    };


    /** Subclass of Allocator that returns a pixelref that allocates its pixel
        memory from the heap. This is the default Allocator invoked by
        allocPixels().
        SkBitmap使用Allocator的派生类--HeapAllocator作为它的默认分配器。其实现如下：
    */
    class HeapAllocator : public Allocator {  
    public:
        virtual bool allocPixelRef(SkBitmap*, SkColorTable*);
    };


    class RLEPixels {
    public:
        RLEPixels(int width, int height);
        virtual ~RLEPixels();


        uint8_t* packedAtY(int y) const {
            SkASSERT((unsigned)y < (unsigned)fHeight);
            return fYPtrs[y];
        }


        // called by subclasses during creation
        void setPackedAtY(int y, uint8_t* addr) {
            SkASSERT((unsigned)y < (unsigned)fHeight);
            fYPtrs[y] = addr;
        }


    private:
        uint8_t** fYPtrs;
        int       fHeight;
    };


private:
    struct MipMap;
    mutable MipMap* fMipMap;


    mutable SkPixelRef* fPixelRef;
    mutable size_t      fPixelRefOffset;
    mutable int         fPixelLockCount;
    // either user-specified (in which case it is not treated as mutable)
    // or a cache of the returned value from fPixelRef->lockPixels()
    mutable void*       fPixels;
    mutable SkColorTable* fColorTable;    // only meaningful for kIndex8


    enum Flags {
        kImageIsOpaque_Flag  = 0x01
    };


    uint32_t    fRowBytes;
    uint32_t    fWidth;
    uint32_t    fHeight;
    uint8_t     fConfig;
    uint8_t     fFlags;
    uint8_t     fBytesPerPixel; // based on config


    /*  Unreference any pixelrefs or colortables
    */
    void freePixels();
    void updatePixelsFromRef() const;


    static SkFixed ComputeMipLevel(SkFixed sx, SkFixed dy);
};