[置顶] android放大镜效果实现

 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);
     }
 }

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);
     }

     @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。

下面我们用这个工具来查看一套PC配置，让你看得更清楚，工程下载地址http://download.csdn.net/detail/hustpzb/4523274