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drawabledrawable = new ShapeDrawable(new OvalShape());drawable.getPaint().setShader(shader);drawable.setBounds(0, 0, RADIUS * 2, RADIUS * 2);}@Overridepublic 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;}@Overridepublic 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

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);}@Overridepublic boolean onTouchEvent(MotionEvent event) {mCurrentX = (int) event.getX();mCurrentY = (int) event.getY();invalidate();return true;}@Overridepublic 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);}
}