Android - alpha/shadow transformation for Picasso (This allows you to draw a transparent black shade over the source image)

AlphaTransformation.java

import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;

import com.squareup.picasso.Transformation;

public class AlphaTransformation implements Transformation {

  /* The shade alpha of black to apply */
  private int mAlpha;

  /**
   * Integer Constructor
   *
   * @param alpha the alpha shade to apply
   */
  public AlphaTransformation(int alpha) {
    // Clamp the alpha value to 0..255
    mAlpha = Math.max(0, Math.min(255, alpha));
  }

  /**
   * Float Constructor
   *
   * @param percent the alpha percentage from 0..1
   */
  public AlphaTransformation(float percent) {
    // Clamp the float value to 0..1
    mAlpha = (int) ((Math.max(0, Math.min(1, percent))) * 255);
  }

  /**
   * Transform the source bitmap into a new bitmap. If you create a new bitmap instance, you must
   * call {@link android.graphics.Bitmap#recycle()} on {@code source}. You may return the original
   * if no transformation is required.
   */
  @Override
  public Bitmap transform(Bitmap source) {
    Paint paint = new Paint();
    Bitmap output =
        Bitmap.createBitmap(source.getWidth(), source.getHeight(), Bitmap.Config.ARGB_8888);

    // Create canvas and draw the source image
    Canvas canvas = new Canvas(output);
    canvas.drawBitmap(source, 0, 0, paint);

    // Setup the paint for painting the shade
    paint.setColor(Color.BLACK);
    paint.setAlpha(mAlpha);

    // Paint the shade
    canvas.drawPaint(paint);

    // Recycle and return
    source.recycle();
    return output;
  }

  /**
   * Returns a unique key for the transformation, used for caching purposes. If the transformation
   * has parameters (e.g. size, scale factor, etc) then these should be part of the key.
   */
  @Override
  public String key() {
    return "shade:" + mAlpha;
  }
}