Android中图形截取的方式介绍

在Android的应用中，有时候我们想仅仅显示一部分图像，这时候就要求图形截图。

1、随意截取图像的方法，以下我们具体介绍一下android中的重要类——Bitmap

public final class

Bitmap

extends Object

implements Parcelable

java.lang.Object

android.graphics.Bitmap



以下是Bitmap的全部应用方法，我们要熟悉记住：

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.

这是我们实现截图图形的重要方法：

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.

第一个參数source就是本来的Bitmap对象，后面的四个參数分别表示截取的范围。



2、另一种方法，不是随意截取图形。而是从图像的一端（上、下、左、右）截取图像。也能够使用图像截取资源，这样的资源须要在res/drawable文件夹中建立一个xml文件

<clip xmlns:android="http://schemas.android.com/apk/res/android"
    android:clipOrientation="horizontal"
    android:drawable="@drawable/ic_launcher"
    android:gravity="left" >
</clip>

然后我们能够通过ClipDrawable获取要截取的图像：

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).

而我们通常所用的Drawable里面有一个方法：

• 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.

这就是设置截取比例的。