Android自定义控件放大镜

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); 
	} 
}