Bitmap

recycle()

呼叫nativeRecycle()釋放該bitmap分配的native物件，清除對畫素資料的引用。不會同步的釋放畫素資料，只是簡單的允許bitmap在沒有其他引用時被垃圾回收。此bitmap被標記為dead，意味著呼叫getPixels()或者setPixels()將會丟擲異常，而且不會繪製。此操作不能回退，所以最好在bitmap不會用到時呼叫。這是一個高階呼叫，通常不應該呼叫，因為通常情況下如果此bitmap沒有被引用，垃圾回收程序會釋放佔用的記憶體空間。

    /**
     * Free the native object associated with
 
 this bitmap, and clear the
     * reference to the pixel data. This will not free the pixel data synchronously;
     * it simply allows it to be garbage collected if there are no other references.
     * The bitmap is marked as "dead", meaning it will throw an exception if
     * getPixels() or setPixels() is
 
 called, and will draw nothing. This operation
     * cannot be reversed, so it should only be called if you are sure there are no
     * further uses for the bitmap. This is an advanced call, and normally need
     * not be called, since the normal GC process will free up this memory when
     * there are no
 
 more references to this bitmap.
     */
     public void recycle() {
        if (!mRecycled && mNativePtr != 0) {
            if (nativeRecycle(mNativePtr)) {
                // return value indicates whether native pixel object was actually recycled.
                // false indicates that it is still in use at the native level and these
                // objects should not be collected now. They will be collected later when the
                // Bitmap itself is collected.
                mBuffer = null;
                mNinePatchChunk = null;
            }
            mRecycled = true;
        }
    }

isRecycled()

判斷點陣圖記憶體是否已經被回收。

checkRecycled

如果已經被回收，則丟擲非法狀態異常IllegalStateException。

    /**
     * This is called by methods that want to throw an exception if the bitmap
     * has already been recycled.
     */
    private void checkRecycled(String errorMessage) {
        if (mRecycled) {
            throw new IllegalStateException(errorMessage);
        }
    }

getWidth() 獲取寬度

getHeight() 獲取高度

getScaledWidth(Canvas canvas)

獲取經指定密度轉換後的寬度

/**
     * Convenience for calling {@link #getScaledWidth(int)} with the target
     * density of the given {@link Canvas}.
     */
    public int getScaledWidth(Canvas canvas) {
        return scaleFromDensity(getWidth(), mDensity, canvas.mDensity);
    }


    /**
     * Convenience for calling {@link #getScaledWidth(int)} with the target
     * density of the given {@link DisplayMetrics}.
     */
    public int getScaledWidth(DisplayMetrics metrics) {
        return scaleFromDensity(getWidth(), mDensity, metrics.densityDpi);
    }

    /**
     * @hide
     */
    static public int scaleFromDensity(int size, int sdensity, int tdensity) {
        if (sdensity == DENSITY_NONE || tdensity == DENSITY_NONE || sdensity == tdensity) {
            return size;
        }

        // Scale by tdensity / sdensity, rounding up.
        return ((size * tdensity) + (sdensity >> 1)) / sdensity;
    }

getScaledHeight(Canvas canvas)

獲取經制定密度轉換後的高度

    /**
     * Convenience for calling {@link #getScaledHeight(int)} with the target
     * density of the given {@link Canvas}.
     */
    public int getScaledHeight(Canvas canvas) {
        return scaleFromDensity(getHeight(), mDensity, canvas.mDensity);
    }

    /**
     * Convenience for calling {@link #getScaledHeight(int)} with the target
     * density of the given {@link DisplayMetrics}.
     */
    public int getScaledHeight(DisplayMetrics metrics) {
        return scaleFromDensity(getHeight(), mDensity, metrics.densityDpi);
    }

getRowBytes()

獲取native點陣圖行畫素的byte數

    /**
     * Return the number of bytes between rows in the bitmap's pixels. Note that
     * this refers to the pixels as stored natively by the bitmap. If you call
     * getPixels() or setPixels(), then the pixels are uniformly treated as
     * 32bit values, packed according to the Color class.
     *
     * <p>As of {@link android.os.Build.VERSION_CODES#KITKAT}, this method
     * should not be used to calculate the memory usage of the bitmap. Instead,
     * see {@link #getAllocationByteCount()}.
     *
     * @return number of bytes between rows of the native bitmap pixels.
     */
    public final int getRowBytes() {
        if (mRecycled) {
            Log.w(TAG, "Called getRowBytes() on a recycle()'d bitmap! This is undefined behavior!");
        }
        return nativeRowBytes(mNativePtr);
    }

getByteCount()

獲取可以儲存此bitmap畫素的最小位元組。返回行畫素x高度。

    /**
     * Returns the minimum number of bytes that can be used to store this bitmap's pixels.
     *
     * <p>As of {@link android.os.Build.VERSION_CODES#KITKAT}, the result of this method can
     * no longer be used to determine memory usage of a bitmap. See {@link
     * #getAllocationByteCount()}.</p>
     */
    public final int getByteCount() {
        // int result permits bitmaps up to 46,340 x 46,340
        return getRowBytes() * getHeight();
    }

getAllocationByteCount()

獲取用來儲存bitmap所分配的記憶體大小。在bitmap的生命週期內此值不會改變。

    /**
     * Returns the size of the allocated memory used to store this bitmap's pixels.
     *
     * <p>This can be larger than the result of {@link #getByteCount()} if a bitmap is reused to
     * decode other bitmaps of smaller size, or by manual reconfiguration. See {@link
     * #reconfigure(int, int, Config)}, {@link #setWidth(int)}, {@link #setHeight(int)}, {@link
     * #setConfig(Bitmap.Config)}, and {@link BitmapFactory.Options#inBitmap
     * BitmapFactory.Options.inBitmap}. If a bitmap is not modified in this way, this value will be
     * the same as that returned by {@link #getByteCount()}.</p>
     *
     * <p>This value will not change over the lifetime of a Bitmap.</p>
     *
     * @see #reconfigure(int, int, Config)
     */
    public final int getAllocationByteCount() {
        if (mBuffer == null) {
            // native backed bitmaps don't support reconfiguration,
            // so alloc size is always content size
            return getByteCount();
        }
        return mBuffer.length;
    }

getConfig()

獲取Config列舉：

• ALPHA_8， 代表8位Alpha點陣圖，每個畫素佔用1byte記憶體
• RGB_565，代表8位RGB點陣圖，每個畫素佔用2byte記憶體
• ARGB_4444 (@deprecated)，代表16位ARGB點陣圖，每個畫素佔用2byte記憶體
• ARGB_8888，代表32位ARGB點陣圖，每個畫素佔用4byte記憶體

    /**
     * If the bitmap's internal config is in one of the public formats, return
     * that config, otherwise return null.
     */
    public final Config getConfig() {
        if (mRecycled) {
            Log.w(TAG, "Called getConfig() on a recycle()'d bitmap! This is undefined behavior!");
        }
        return Config.nativeToConfig(nativeConfig(mNativePtr));
    }

hasAlpha()

檢測bitmap是否支援畫素級別透明。

    /** Returns true if the bitmap's config supports per-pixel alpha, and
     * if the pixels may contain non-opaque alpha values. For some configs,
     * this is always false (e.g. RGB_565), since they do not support per-pixel
     * alpha. However, for configs that do, the bitmap may be flagged to be
     * known that all of its pixels are opaque. In this case hasAlpha() will
     * also return false. If a config such as ARGB_8888 is not so flagged,
     * it will return true by default.
     */
    public final boolean hasAlpha() {
        if (mRecycled) {
            Log.w(TAG, "Called hasAlpha() on a recycle()'d bitmap! This is undefined behavior!");
        }
        return nativeHasAlpha(mNativePtr);
    }

setHasAlpha(boolean hasAlpha)

設定bitmap是否支援畫素級別透明

    /**
     * Tell the bitmap if all of the pixels are known to be opaque (false)
     * or if some of the pixels may contain non-opaque alpha values (true).
     * Note, for some configs (e.g. RGB_565) this call is ignored, since it
     * does not support per-pixel alpha values.
     *
     * This is meant as a drawing hint, as in some cases a bitmap that is known
     * to be opaque can take a faster drawing case than one that may have
     * non-opaque per-pixel alpha values.
     */
    public void setHasAlpha(boolean hasAlpha) {
        checkRecycled("setHasAlpha called on a recycled bitmap");
        nativeSetHasAlpha(mNativePtr, hasAlpha, mRequestPremultiplied);
    }

eraseColor(@ColorInt int c)

用顏色值填充bitmap的畫素。

    /**
     * Fills the bitmap's pixels with the specified {@link Color}.
     *
     * @throws IllegalStateException if the bitmap is not mutable.
     */
    public void eraseColor(@ColorInt int c) {
        checkRecycled("Can't erase a recycled bitmap");
        if (!isMutable()) {
            throw new IllegalStateException("cannot erase immutable bitmaps");
        }
        nativeErase(mNativePtr, c);
    }

getPixel(int x, int y)

獲取指定位置畫素的顏色值。

    /**
     * Returns the {@link Color} at the specified location. Throws an exception
     * if x or y are out of bounds (negative or >= to the width or height
     * respectively). The returned color is a non-premultiplied ARGB value.
     *
     * @param x    The x coordinate (0...width-1) of the pixel to return
     * @param y    The y coordinate (0...height-1) of the pixel to return
     * @return     The argb {@link Color} at the specified coordinate
     * @throws IllegalArgumentException if x, y exceed the bitmap's bounds
     */
    @ColorInt
    public int getPixel(int x, int y) {
        checkRecycled("Can't call getPixel() on a recycled bitmap");
        checkPixelAccess(x, y);
        return nativeGetPixel(mNativePtr, x, y);
    }

setPixel(int x, int y, @ColorInt int color)

設定指定位置畫素的顏色值。

    /**
     * <p>Write the specified {@link Color} into the bitmap (assuming it is
     * mutable) at the x,y coordinate. The color must be a
     * non-premultiplied ARGB value.</p>
     *
     * @param x     The x coordinate of the pixel to replace (0...width-1)
     * @param y     The y coordinate of the pixel to replace (0...height-1)
     * @param color The ARGB color to write into the bitmap
     *
     * @throws IllegalStateException if the bitmap is not mutable
     * @throws IllegalArgumentException if x, y are outside of the bitmap's
     *         bounds.
     */
    public void setPixel(int x, int y, @ColorInt int color) {
        checkRecycled("Can't call setPixel() on a recycled bitmap");
        if (!isMutable()) {
            throw new IllegalStateException();
        }
        checkPixelAccess(x, y);
        nativeSetPixel(mNativePtr, x, y, color);
    }

writeToParcel(Parcel p, int flags)

打包bitmap

    /**
     * Write the bitmap and its pixels to the parcel. The bitmap can be
     * rebuilt from the parcel by calling CREATOR.createFromParcel().
     * @param p    Parcel object to write the bitmap data into
     */
    public void writeToParcel(Parcel p, int flags) {
        checkRecycled("Can't parcel a recycled bitmap");
        if (!nativeWriteToParcel(mNativePtr, mIsMutable, mDensity, p)) {
            throw new RuntimeException("native writeToParcel failed");
        }
    }

extractAlpha()

獲取原bitmap的alpha通道資料最為新的bitmap。

    /**
     * Returns a new bitmap that captures the alpha values of the original.
     * This may be drawn with Canvas.drawBitmap(), where the color(s) will be
     * taken from the paint that is passed to the draw call.
     *
     * @return new bitmap containing the alpha channel of the original bitmap.
     */
    @CheckResult
    public Bitmap extractAlpha() {
        return extractAlpha(null, null);
    }

#

和另外一個bitmap比較二者是否相同。
    /**
     *  Given another bitmap, return true if it has the same dimensions, config,
     *  and pixel data as this bitmap. If any of those differ, return false.
     *  If other is null, return false.
     */
    public boolean sameAs(Bitmap other) {
        checkRecycled("Can't call sameAs on a recycled bitmap!");
        if (this == other) return true;
        if (other == null) return false;
        if (other.isRecycled()) {
            throw new IllegalArgumentException("Can't compare to a recycled bitmap!");
        }
        return nativeSameAs(mNativePtr, other.mNativePtr);
    }

prepareToDraw()

繪製準備：重建該bitmap相關聯的快取來繪製。在可清除的bitmap中，此方法會嘗試確保畫素已經被解碼。

    /**
     * Rebuilds any caches associated with the bitmap that are used for
     * drawing it. In the case of purgeable bitmaps, this call will attempt to
     * ensure that the pixels have been decoded.
     * If this is called on more than one bitmap in sequence, the priority is
     * given in LRU order (i.e. the last bitmap called will be given highest
     * priority).
     *
     * For bitmaps with no associated caches, this call is effectively a no-op,
     * and therefore is harmless.
     */
    public void prepareToDraw() {
        checkRecycled("Can't prepareToDraw on a recycled bitmap!");
        // Kick off an update/upload of the bitmap outside of the normal
        // draw path.
        nativePrepareToDraw(mNativePtr);
    }

CompressFormat

bitmap壓縮格式：JPEG，PNG，WEBP（谷歌推出的圖片格式，小體積高質量，豆瓣電影的海報使用的此格式）

    /**
     * Specifies the known formats a bitmap can be compressed into
     */
    public enum CompressFormat {
        JPEG    (0),
        PNG     (1),
        WEBP    (2);

        CompressFormat(int nativeInt) {
            this.nativeInt = nativeInt;
        }
        final int nativeInt;
    }

compress(CompressFormat format, int quality, OutputStream stream)

壓縮bitmap。

    /**
     * Write a compressed version of the bitmap to the specified outputstream.
     * If this returns true, the bitmap can be reconstructed by passing a
     * corresponding inputstream to BitmapFactory.decodeStream(). Note: not
     * all Formats support all bitmap configs directly, so it is possible that
     * the returned bitmap from BitmapFactory could be in a different bitdepth,
     * and/or may have lost per-pixel alpha (e.g. JPEG only supports opaque
     * pixels).
     *
     * @param format   The format of the compressed image
     * @param quality  Hint to the compressor, 0-100. 0 meaning compress for
     *                 small size, 100 meaning compress for max quality. Some
     *                 formats, like PNG which is lossless, will ignore the
     *                 quality setting
     * @param stream   The outputstream to write the compressed data.
     * @return true if successfully compressed to the specified stream.
     */
    public boolean compress(CompressFormat format, int quality, OutputStream stream) {
        checkRecycled("Can't compress a recycled bitmap");
        // do explicit check before calling the native method
        if (stream == null) {
            throw new NullPointerException();
        }
        if (quality < 0 || quality > 100) {
            throw new IllegalArgumentException("quality must be 0..100");
        }
        Trace.traceBegin(Trace.TRACE_TAG_RESOURCES, "Bitmap.compress");
        boolean result = nativeCompress(mNativePtr, format.nativeInt,
                quality, stream, new byte[WORKING_COMPRESS_STORAGE]);
        Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);
        return result;
    }

BitmapFactory

inMutable

配置bitmap是否可修改

        /**
         * If set, decode methods will always return a mutable Bitmap instead of
         * an immutable one. This can be used for instance to programmatically apply
         * effects to a Bitmap loaded through BitmapFactory.
         */
        @SuppressWarnings({"UnusedDeclaration"}) // used in native code
        public boolean inMutable;

inJustDecodeBounds

如果設定為true，不獲取圖片，不分配記憶體，但會返回圖片的高度寬度資訊。

        /**
         * If set to true, the decoder will return null (no bitmap), but
         * the out... fields will still be set, allowing the caller to query
         * the bitmap without having to allocate the memory for its pixels.
         */
        public boolean inJustDecodeBounds;

inSampleSize

圖片縮放倍數

        /**
         * If set to a value > 1, requests the decoder to subsample the original
         * image, returning a smaller image to save memory. The sample size is
         * the number of pixels in either dimension that correspond to a single
         * pixel in the decoded bitmap. For example, inSampleSize == 4 returns
         * an image that is 1/4 the width/height of the original, and 1/16 the
         * number of pixels. Any value <= 1 is treated the same as 1. Note: the
         * decoder uses a final value based on powers of 2, any other value will
         * be rounded down to the nearest power of 2.
         */
        public int inSampleSize;

inDither, @deprecated

抖動解碼

        /**
         * @deprecated As of {@link android.os.Build.VERSION_CODES#N}, this is
         * ignored.
         *
         * In {@link android.os.Build.VERSION_CODES#M} and below, if dither is
         * true, the decoder will attempt to dither the decoded image.
         */
        public boolean inDither;

inDensity

用於點陣圖的畫素壓縮比。

        /**
         * The pixel density to use for the bitmap.  This will always result
         * in the returned bitmap having a density set for it (see
         * {@link Bitmap#setDensity(int) Bitmap.setDensity(int)}).  In addition,
         * if {@link #inScaled} is set (which it is by default} and this
         * density does not match {@link #inTargetDensity}, then the bitmap
         * will be scaled to the target density before being returned.
         * 
         * <p>If this is 0,
         * {@link BitmapFactory#decodeResource(Resources, int)}, 
         * {@link BitmapFactory#decodeResource(Resources, int, android.graphics.BitmapFactory.Options)},
         * and {@link BitmapFactory#decodeResourceStream}
         * will fill in the density associated with the resource.  The other
         * functions will leave it as-is and no density will be applied.
         *
         * @see #inTargetDensity
         * @see #inScreenDensity
         * @see #inScaled
         * @see Bitmap#setDensity(int)
         * @see android.util.DisplayMetrics#densityDpi
         */
        public int inDensity;

inTargetDensity

用於目標點陣圖的畫素壓縮比（要生成的點陣圖）

        /**
         * The pixel density of the destination this bitmap will be drawn to.
         * This is used in conjunction with {@link #inDensity} and
         * {@link #inScaled} to determine if and how to scale the bitmap before
         * returning it.
         * 
         * <p>If this is 0,
         * {@link BitmapFactory#decodeResource(Resources, int)}, 
         * {@link BitmapFactory#decodeResource(Resources, int, android.graphics.BitmapFactory.Options)},
         * and {@link BitmapFactory#decodeResourceStream}
         * will fill in the density associated the Resources object's
         * DisplayMetrics.  The other
         * functions will leave it as-is and no scaling for density will be
         * performed.
         * 
         * @see #inDensity
         * @see #inScreenDensity
         * @see #inScaled
         * @see android.util.DisplayMetrics#densityDpi
         */
        public int inTargetDensity;

inScreenDensity

當前螢幕的畫素密度

        /**
         * The pixel density of the actual screen that is being used.  This is
         * purely for applications running in density compatibility code, where
         * {@link #inTargetDensity} is actually the density the application
         * sees rather than the real screen density.
         * 
         * <p>By setting this, you
         * allow the loading code to avoid scaling a bitmap that is currently
         * in the screen density up/down to the compatibility density.  Instead,
         * if {@link #inDensity} is the same as {@link #inScreenDensity}, the
         * bitmap will be left as-is.  Anything using the resulting bitmap
         * must also used {@link Bitmap#getScaledWidth(int)
         * Bitmap.getScaledWidth} and {@link Bitmap#getScaledHeight
         * Bitmap.getScaledHeight} to account for any different between the
         * bitmap's density and the target's density.
         * 
         * <p>This is never set automatically for the caller by
         * {@link BitmapFactory} itself.  It must be explicitly set, since the
         * caller must deal with the resulting bitmap in a density-aware way.
         * 
         * @see #inDensity
         * @see #inTargetDensity
         * @see #inScaled
         * @see android.util.DisplayMetrics#densityDpi
         */
        public int inScreenDensity;

inScaled

設定為true時進行圖片壓縮，從inDensity到inTargetDensity

        /**
         * When this flag is set, if {@link #inDensity} and
         * {@link #inTargetDensity} are not 0, the
         * bitmap will be scaled to match {@link #inTargetDensity} when loaded,
         * rather than relying on the graphics system scaling it each time it
         * is drawn to a Canvas.
         *
         * <p>BitmapRegionDecoder ignores this flag, and will not scale output
         * based on density. (though {@link #inSampleSize} is supported)</p>
         *
         * <p>This flag is turned on by default and should be turned off if you need
         * a non-scaled version of the bitmap.  Nine-patch bitmaps ignore this
         * flag and are always scaled.
         *
         * <p>If {@link #inPremultiplied} is set to false, and the image has alpha,
         * setting this flag to true may result in incorrect colors.
         */
        public boolean inScaled;

inPurgeable

當儲存Pixel的記憶體空間在系統記憶體不足時是否可以被回收

        /**
         * @deprecated As of {@link android.os.Build.VERSION_CODES#LOLLIPOP}, this is
         * ignored.
         *
         * In {@link android.os.Build.VERSION_CODES#KITKAT} and below, if this
         * is set to true, then the resulting bitmap will allocate its
         * pixels such that they can be purged if the system needs to reclaim
         * memory. In that instance, when the pixels need to be accessed again
         * (e.g. the bitmap is drawn, getPixels() is called), they will be
         * automatically re-decoded.
         *
         * <p>For the re-decode to happen, the bitmap must have access to the
         * encoded data, either by sharing a reference to the input
         * or by making a copy of it. This distinction is controlled by
         * inInputShareable. If this is true, then the bitmap may keep a shallow
         * reference to the input. If this is false, then the bitmap will
         * explicitly make a copy of the input data, and keep that. Even if
         * sharing is allowed, the implementation may still decide to make a
         * deep copy of the input data.</p>
         *
         * <p>While inPurgeable can help avoid big Dalvik heap allocations (from
         * API level 11 onward), it sacrifices performance predictability since any
         * image that the view system tries to draw may incur a decode delay which
         * can lead to dropped frames. Therefore, most apps should avoid using
         * inPurgeable to allow for a fast and fluid UI. To minimize Dalvik heap
         * allocations use the {@link #inBitmap} flag instead.</p>
         *
         * <p class="note"><strong>Note:</strong> This flag is ignored when used
         * with {@link #decodeResource(Resources, int,
         * android.graphics.BitmapFactory.Options)} or {@link #decodeFile(String,
         * android.graphics.BitmapFactory.Options)}.</p>
         */
        @Deprecated
        public boolean inPurgeable;

inInputShareable

inPurgeable為true情況下才生效，是否可以共享一個InputStream

        /**
         * @deprecated As of {@link android.os.Build.VERSION_CODES#LOLLIPOP}, this is
         * ignored.
         *
         * In {@link android.os.Build.VERSION_CODES#KITKAT} and below, this
         * field works in conjuction with inPurgeable. If inPurgeable is false,
         * then this field is ignored. If inPurgeable is true, then this field
         * determines whether the bitmap can share a reference to the input
         * data (inputstream, array, etc.) or if it must make a deep copy.
         */
        @Deprecated
        public boolean inInputShareable;

inPreferQualityOverSpeed

為true則優先保證Bitmap質量其次是解碼速度。

        /**
         * @deprecated As of {@link android.os.Build.VERSION_CODES#N}, this is
         * ignored.  The output will always be high quality.
         *
         * In {@link android.os.Build.VERSION_CODES#M} and below, if
         * inPreferQualityOverSpeed is set to true, the decoder will try to
         * decode the reconstructed image to a higher quality even at the
         * expense of the decoding speed. Currently the field only affects JPEG
         * decode, in the case of which a more accurate, but slightly slower,
         * IDCT method will be used instead.
         */
        public boolean inPreferQualityOverSpeed;

decodeFile(String pathName, Options opts)

從檔案讀取圖片

    /**
     * Decode a file path into a bitmap. If the specified file name is null,
     * or cannot be decoded into a bitmap, the function returns null.
     *
     * @param pathName complete path name for the file to be decoded.
     * @param opts null-ok; Options that control downsampling and whether the
     *             image should be completely decoded, or just is size returned.
     * @return The decoded bitmap, or null if the image data could not be
     *         decoded, or, if opts is non-null, if opts requested only the
     *         size be returned (in opts.outWidth and opts.outHeight)
     */
    public static Bitmap decodeFile(String pathName, Options opts) {
        Bitmap bm = null;
        InputStream stream = null;
        try {
            stream = new FileInputStream(pathName);
            bm = decodeStream(stream, null, opts);
        } catch (Exception e) {
            /*  do nothing.
                If the exception happened on open, bm will be null.
            */
            Log.e("BitmapFactory", "Unable to decode stream: " + e);
        } finally {
            if (stream != null) {
                try {
                    stream.close();
                } catch (IOException e) {
                    // do nothing here
                }
            }
        }
        return bm;
    }

decodeResource

從res資原始檔讀取圖片。
載入的圖片可能會經過縮放，該縮放目前是放在 java 層做的，效率比較低，而且需要消耗 java 層的記憶體。因此，如果大量使用該介面載入圖片，容易導致OOM錯誤

    /**
     * Synonym for opening the given resource and calling
     * {@link #decodeResourceStream}.
     *
     * @param res   The resources object containing the image data
     * @param id The resource id of the image data
     * @param opts null-ok; Options that control downsampling and whether the
     *             image should be completely decoded, or just is size returned.
     * @return The decoded bitmap, or null if the image data could not be
     *         decoded, or, if opts is non-null, if opts requested only the
     *         size be returned (in opts.outWidth and opts.outHeight)
     */
    public static Bitmap decodeResource(Resources res, int id, Options opts) {
        Bitmap bm = null;
        InputStream is = null; 

        try {
            final TypedValue value = new TypedValue();
            is = res.openRawResource(id, value);

            bm = decodeResourceStream(res, value, is, null, opts);
        } catch (Exception e) {
            /*  do nothing.
                If the exception happened on open, bm will be null.
                If it happened on close, bm is still valid.
            */
        } finally {
            try {
                if (is != null) is.close();
            } catch (IOException e) {
                // Ignore
            }
        }

        if (bm == null && opts != null && opts.inBitmap != null) {
            throw new IllegalArgumentException("Problem decoding into existing bitmap");
        }

        return bm;
    }

decodeByteArray

從陣列讀取圖片

    /**
     * Decode an immutable bitmap from the specified byte array.
     *
     * @param data byte array of compressed image data
     * @param offset offset into imageData for where the decoder should begin
     *               parsing.
     * @param length the number of bytes, beginning at offset, to parse
     * @param opts null-ok; Options that control downsampling and whether the
     *             image should be completely decoded, or just is size returned.
     * @return The decoded bitmap, or null if the image data could not be
     *         decoded, or, if opts is non-null, if opts requested only the
     *         size be returned (in opts.outWidth and opts.outHeight)
     */
    public static Bitmap decodeByteArray(byte[] data, int offset, int length, Options opts) {
        if ((offset | length) < 0 || data.length < offset + length) {
            throw new ArrayIndexOutOfBoundsException();
        }

        Bitmap bm;

        Trace.traceBegin(Trace.TRACE_TAG_GRAPHICS, "decodeBitmap");
        try {
            bm = nativeDecodeByteArray(data, offset, length, opts);

            if (bm == null && opts != null && opts.inBitmap != null) {
                throw new IllegalArgumentException("Problem decoding into existing bitmap");
            }
            setDensityFromOptions(bm, opts);
        } finally {
            Trace.traceEnd(Trace.TRACE_TAG_GRAPHICS);
        }

        return bm;
    }

decodeStream(InputStream is, Rect outPadding, Options opts)

從輸入流讀取圖片。
不會對所載入的圖片進行縮放，相比之下佔用記憶體少，效率更高。

    /**
     * Decode an input stream into a bitmap. If the input stream is null, or
     * cannot be used to decode a bitmap, the function returns null.
     * The stream's position will be where ever it was after the encoded data
     * was read.
     *
     * @param is The input stream that holds the raw data to be decoded into a
     *           bitmap.
     * @param outPadding If not null, return the padding rect for the bitmap if
     *                   it exists, otherwise set padding to [-1,-1,-1,-1]. If
     *                   no bitmap is returned (null) then padding is
     *                   unchanged.
     * @para