Android放大镜的实现代码

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);
 }
}

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);  
 }
}