Android放大镜的实现

package chroya.demo.magnifier;       import android.content.Context;   import android.graphics.Bitmap;   import android.graphics.BitmapFactory;   import android.graphics.BitmapShader;   import android.graphics.Canvas;   import android.graphics.Matrix;   import android.graphics.Shader.TileMode;   import android.graphics.drawable.ShapeDrawable;   import android.graphics.drawable.shapes.OvalShape;   import android.view.MotionEvent;   import android.view.View;       /**  * 放大镜实现方式1  * @author chroya  *  */    public  class ShaderView extends View{   private Bitmap bitmap;   private ShapeDrawable drawable;   //放大镜的半径     private  static  final  int RADIUS = 80;   //放大倍数     private  static  final  int FACTOR = 3;   private Matrix matrix = new Matrix();       public ShaderView(Context context) {   super(context);   Bitmap bmp = BitmapFactory.decodeResource(getResources(), R.drawable.show);   bitmap = bmp;   BitmapShader shader = new BitmapShader(   Bitmap.createScaledBitmap(bmp, bmp.getWidth()*FACTOR,   bmp.getHeight()*FACTOR, true), TileMode.CLAMP, TileMode.CLAMP);   //圆形的drawable     drawable = new ShapeDrawable(new OvalShape());   drawable.getPaint().setShader(shader);   drawable.setBounds(0, 0, RADIUS*2, RADIUS*2);   }       @Override    public  boolean onTouchEvent(MotionEvent event) {   final  int x = (int) event.getX();   final  int y = (int) event.getY();   //这个位置表示的是，画shader的起始位置     matrix.setTranslate(RADIUS-x*FACTOR, RADIUS-y*FACTOR);   drawable.getPaint().getShader().setLocalMatrix(matrix);   //bounds，就是那个圆的外切矩形     drawable.setBounds(x-RADIUS, y-RADIUS, x+RADIUS, y+RADIUS);   invalidate();   return  true;   }       @Override    public  void onDraw(Canvas canvas) {   super.onDraw(canvas);   canvas.drawBitmap(bitmap, 0, 0, null);   drawable.draw(canvas);   }   }

基本原理就是使用ShapeDrawable构造一个圆形的drawable，然后它的paint的shader设置为将要放大的图片，然后就是简单的位置移动问题了。放大镜的半径和放大倍数都可以在代码里面修改，代码都有注释，应该很好理解了。

不过，一个问题如果只有一种解决方法的话，那未免有点令人沮丧，想玩点另类的都不行。
玩程序就得玩出个性，玩出激情。哈哈，废话太多，切回正题。

再来看看放大镜的另外一种实现吧

package chroya.demo.magnifier;       import android.content.Context;   import android.graphics.Bitmap;   import android.graphics.BitmapFactory;   import android.graphics.Canvas;   import android.graphics.Matrix;   import android.graphics.Path;   import android.graphics.Path.Direction;   import android.view.MotionEvent;   import android.view.View;       /**  * 放大镜实现方式2  * @author chroya  *  */    public  class PathView extends View{   private Path mPath = new Path();   private Matrix matrix = new Matrix();   private Bitmap bitmap;   //放大镜的半径     private  static  final  int RADIUS = 80;   //放大倍数     private  static  final  int FACTOR = 2;   private  int mCurrentX, mCurrentY;       public PathView(Context context) {   super(context);   mPath.addCircle(RADIUS, RADIUS, RADIUS, Direction.CW);   matrix.setScale(FACTOR, FACTOR);       bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.show);   }       @Override    public  boolean onTouchEvent(MotionEvent event) {   mCurrentX = (int) event.getX();   mCurrentY = (int) event.getY();       invalidate();   return  true;   }       @Override    public  void onDraw(Canvas canvas) {   super.onDraw(canvas);   //底图     canvas.drawBitmap(bitmap, 0, 0, null);   //剪切     canvas.translate(mCurrentX - RADIUS, mCurrentY - RADIUS);   canvas.clipPath(mPath);   //画放大后的图     canvas.translate(RADIUS-mCurrentX*FACTOR, RADIUS-mCurrentY*FACTOR);   canvas.drawBitmap(bitmap, matrix, null);   }   }

这里使用的是Path类，将canvas剪切出一块圆形区域，在其上绘制放大的部分。
两种方式的效果都一样，如图：

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