Rounded Corner Image Transformation for square's Picasso

RoundedTransformation.java

import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.BitmapShader;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.RectF;
import android.graphics.Shader;

// enables hardware accelerated rounded corners
// original idea here : http://www.curious-creature.org/2012/12/11/android-recipe-1-image-with-rounded-corners/
public class RoundedTransformation implements com.squareup.picasso.Transformation {
    
    // radius is corner radii in dp
    // margin is the board in dp
    public RoundedTransformation(final int radius, final int margin) {
        _radius = radius;
		_margin = margin;
		_key = "rounded(radius=" + radius + ", margin=" + margin + ")";
    }

    @Override
    public Bitmap transform(final Bitmap source) {
        final Paint paint = new Paint();
		paint.setAntiAlias(true);
		paint.setShader(new BitmapShader(source, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP));

		Bitmap output = Bitmap.createBitmap(source.getWidth(), source.getHeight(), Bitmap.Config.ARGB_8888);
		Canvas canvas = new Canvas(output);
		canvas.drawRoundRect(new RectF(_margin, _margin, source.getWidth() - _margin, source.getHeight() - _margin),
							 _radius, _radius, paint);

		if (source != output) {
			source.recycle();
		}

		return output;
    }

    @Override
    public String key() {
        return _key;
    }
    
    private final int _radius;
	private final int _margin;
	private final String _key;
}