public class ShaderView extends View {
  private final Bitmap bitmap;
  private final 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 final Matrix matrix = new Matrix();
 
  public ShaderView(Context context) {
   super(context);
   Bitmap bmp = BitmapFactory.decodeResource(getResources(),R.drawable.demo);
   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);
 }
}

public class PathView extends View {
  private final Path mPath = new Path();
  private final Matrix matrix = new Matrix();
  private final 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.demo);
  }
 
 @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);
 }
}