Android 从源码分析Bitmap和BitmapFactory常用API

• 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()

获取native位图行像素的byte数

/**

• 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.

• 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()

获取可以存储此bitmap像素的最小字节。返回行像素x高度。

/**

• Returns the minimum number of bytes that can be used to store this bitmap’s pixels.

• 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()}.

*/

public final int getByteCount() {

// int result permits bitmaps up to 46,340 x 46,340

return getRowBytes() * getHeight();

}

getAllocationByteCount()

获取用来存储bitmap所分配的内存大小。在bitmap的生命周期内此值不会改变。

/**

• Returns the size of the allocated memory used to store this bitmap’s pixels.

• 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()}.

• This value will not change over the lifetime of a Bitmap.

• @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()

获取Config枚举：

• ALPHA_8， 代表8位Alpha位图，每个像素占用1byte内存

• RGB_565，代表8位RGB位图，每个像素占用2byte内存

• ARGB_4444 (@deprecated)，代表16位ARGB位图，每个像素占用2byte内存

• ARGB_8888，代表32位ARGB位图，每个像素占用4byte内存

/**

• 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()

检测bitmap是否支持像素级别透明。

/** Returns true if the bitmap’s config supports per-pixel alpha, and

• if the pixels may contain non-opaque alpha values. For some configs,