代码如下：

 

public Bitmap transform(Bitmap source) {	        int size = Math.min(source.getWidth(), source.getHeight());	        int x = (source.getWidth() - size) / 2;	        int y = (source.getHeight() - size) / 2;	        Bitmap squaredBitmap = Bitmap.createBitmap(source, x, y, size, size);	        if (squaredBitmap != source) {	            source.recycle();	        }	        Bitmap bitmap = Bitmap.createBitmap(size, size, source.getConfig());	        Canvas canvas = new Canvas(bitmap);	        Paint paint = new Paint();	        BitmapShader shader = new BitmapShader(squaredBitmap, BitmapShader.TileMode.CLAMP, BitmapShader.TileMode.CLAMP);	        paint.setShader(shader);	        paint.setAntiAlias(true);	        float r = size/2f;	        canvas.drawCircle(r, r, r, paint);	        squaredBitmap.recycle();	        return bitmap;	    }