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 {
    private final int radius;
    private final int margin;  // dp

    // radius is corner radii in dp
    // margin is the board in dp
    public RoundedTransformation(final int radius, final int margin) {
        this.radius = radius;
        this.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(), 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 "rounded";
    }
}

If anybody is looking for option to apply rounded corner to only top and bottom corners individually, check following gist

https://gist.github.com/amardeshbd/06b491d4adb568b1b226a20d4953a180

Thanks for this! Here's my slight modification to convert to Kotlin and have appropriate defaults without needing to know the radius beforehand. Used to show pretty images in push notifications!

class RoundedTransformation(private val radius: Float? = null, private val margin: Float = 0f) : Transformation {
    override fun transform(source: Bitmap): Bitmap {
        val paint = Paint().apply {
            isAntiAlias = true
            shader = BitmapShader(source, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP)
        }
        val output = Bitmap.createBitmap(source.width, source.height, Config.ARGB_8888)
        Canvas(output).drawRoundRect(margin, margin, source.width - margin, source.height - margin,
                radius ?: source.width.toFloat() / 2, radius ?: source.height.toFloat() / 2,
                paint)
        if (source != output) {
            source.recycle()
        }
        return output
    }

    override fun key(): String {
        return "rounded(radius=$radius, margin=$margin)"
    }
}

Thanks @mensly