在Android的應用中，有時候我們想只顯示一部分圖像，這時候就要求圖形截圖。

1、任意截取圖像的方法，下面我們詳細介紹一下android中的重要類——Bitmap

public final class

Bitmap

extends Object
implements Parcelable java.lang.Object android.graphics.Bitmap

下面是Bitmap的所有應用方法，我們要熟悉記住：
公有方法 boolean compress(Bitmap.CompressFormat format, int quality, OutputStream stream) Write a compressed version of the bitmap to the specified outputstream. Bitmap copy(Bitmap.Config config, boolean isMutable) Tries to make a new bitmap based on the dimensions of this bitmap, setting the new bitmap's config to the one specified, and then copying this bitmap's pixels into the new bitmap. void copyPixelsFromBuffer(Buffer src) Copy the pixels from the buffer, beginning at the current position, overwriting the bitmap's pixels. void copyPixelsToBuffer(Buffer dst) Copy the bitmap's pixels into the specified buffer (allocated by the caller). static Bitmap createBitmap(Bitmap source, int x, int y, int width, int height, Matrix m, boolean filter) Returns an immutable bitmap from subset of the source bitmap, transformed by the optional matrix. static Bitmap createBitmap(int width, int height, Bitmap.Config config) Returns a mutable bitmap with the specified width and height. static Bitmap createBitmap(Bitmap source, int x, int y, int width, int height) Returns an immutable bitmap from the specified subset of the source bitmap. static Bitmap createBitmap(int[] colors, int offset, int stride, int width, int height, Bitmap.Config config) Returns a immutable bitmap with the specified width and height, with each pixel value set to the corresponding value in the colors array. static Bitmap createBitmap(Bitmap src) Returns an immutable bitmap from the source bitmap. static Bitmap createBitmap(int[] colors, int width, int height, Bitmap.Config config) Returns a immutable bitmap with the specified width and height, with each pixel value set to the corresponding value in the colors array. static Bitmap createScaledBitmap(Bitmap src, int dstWidth, int dstHeight, boolean filter) Creates a new bitmap, scaled from an existing bitmap. int describeContents() No special parcel contents. void eraseColor(int c) Fills the bitmap's pixels with the specified Color. Bitmap extractAlpha() Returns a new bitmap that captures the alpha values of the original. Bitmap extractAlpha(Paint paint, int[] offsetXY) Returns a new bitmap that captures the alpha values of the original. final Bitmap.Config getConfig() If the bitmap's internal config is in one of the public formats, return that config, otherwise return null. int getDensity()

Returns the density for this bitmap.

final int getHeight() Returns the bitmap's height byte[] getNinePatchChunk() Returns an optional array of private data, used by the UI system for some bitmaps. int getPixel(int x, int y) Returns the Color at the specified location. void getPixels(int[] pixels, int offset, int stride, int x, int y, int width, int height) Returns in pixels[] a copy of the data in the bitmap. final int getRowBytes() Return the number of bytes between rows in the bitmap's pixels. int getScaledHeight(int targetDensity) Convenience method that returns the height of this bitmap divided by the density scale factor. int getScaledHeight(DisplayMetrics metrics) Convenience for calling getScaledHeight(int) with the target density of the given DisplayMetrics. int getScaledHeight(Canvas canvas) Convenience for calling getScaledHeight(int) with the target density of the given Canvas. int getScaledWidth(DisplayMetrics metrics) Convenience for calling getScaledWidth(int) with the target density of the given DisplayMetrics. int getScaledWidth(int targetDensity) Convenience method that returns the width of this bitmap divided by the density scale factor. int getScaledWidth(Canvas canvas) Convenience for calling getScaledWidth(int) with the target density of the given Canvas. final int getWidth() Returns the bitmap's width final boolean hasAlpha() Returns true if the bitmap's config supports per-pixel alpha, and if the pixels may contain non-opaque alpha values. final boolean isMutable() Returns true if the bitmap is marked as mutable (i.e. final boolean isRecycled() Returns true if this bitmap has been recycled. void prepareToDraw() Rebuilds any caches associated with the bitmap that are used for drawing it. void recycle() Free up the memory associated with this bitmap's pixels, and mark the bitmap as "dead", meaning it will throw an exception if getPixels() or setPixels() is called, and will draw nothing. void setDensity(int density)

Specifies the density for this bitmap.

void setPixel(int x, int y, int color) Write the specified Color into the bitmap (assuming it is mutable) at the x,y coordinate. void setPixels(int[] pixels, int offset, int stride, int x, int y, int width, int height) Replace pixels in the bitmap with the colors in the array. void writeToParcel(Parcel p, int flags) Write the bitmap and its pixels to the parcel. 這是我們實現截圖圖形的重要方法：
static Bitmap createBitmap(Bitmap source, int x, int y, int width, int height) Returns an immutable bitmap from the specified subset of the source bitmap. 第一個參數source就是本來的Bitmap對象，後面的四個參數分別表示截取的范圍。

2、還有一種方法，不是任意截取圖形，而是從圖像的一端（上、下、左、右）截取圖像，也可以使用圖像截取資源，這種資源需要在res/drawable目錄中建立一個xml文件

然後我們可以通過ClipDrawable獲取要截取的圖像：
public class

ClipDrawable

extends Drawable
implements Drawable.Callback java.lang.Object android.graphics.drawable.Drawable android.graphics.drawable.ClipDrawable
公有方法 void draw(Canvas canvas) Draw in its bounds (set via setBounds) respecting optional effects such as alpha (set via setAlpha) and color filter (set via setColorFilter). int getChangingConfigurations() Return a mask of the configuration parameters for which this drawable may change, requiring that it be re-created. Drawable.ConstantState getConstantState() int getIntrinsicHeight() Return the intrinsic height of the underlying drawable object. int getIntrinsicWidth() Return the intrinsic width of the underlying drawable object. int getOpacity() Return the opacity/transparency of this Drawable. boolean getPadding(Rect padding) Return in padding the insets suggested by this Drawable for placing content inside the drawable's bounds. void inflate(Resources r, XmlPullParser parser, AttributeSet attrs) void invalidateDrawable(Drawable who) Called when the drawable needs to be redrawn. boolean isStateful() Indicates whether this view will change its appearance based on state. void scheduleDrawable(Drawable who, Runnable what, long when) A Drawable can call this to schedule the next frame of its animation. void setAlpha(int alpha) Specify an alpha value for the drawable. void setColorFilter(ColorFilter cf) Specify an optional colorFilter for the drawable. boolean setVisible(boolean visible, boolean restart) Set whether this Drawable is visible. void unscheduleDrawable(Drawable who, Runnable what) A Drawable can call this to unschedule an action previously scheduled with scheduleDrawable(Drawable, Runnable, long). 而我們通常所用的Drawable裡面有一個方法：

• The setLevel(int) method allows the client to supply a single continuous controller that can modify the Drawable is displayed, such as a battery level or progress level. Some drawables may modify their imagery based on the current level. 這就是設置截取比例的。