code: private static Drawable getRippleMask(int color, int radius) {
          float[] outerRadius = new float[8];
          Arrays.fill(outerRadius, radius);
          RoundRectShape r = new RoundRectShape(outerRadius, null, null);
          ShapeDrawable shapeDrawable = new ShapeDrawable(r);
          shapeDrawable.getPaint().setColor(color);
          return shapeDrawable;
      }
docs: helper to create an ripple mask with the given color and radius
  
  @param color  the color
  @param radius the radius
  @return the mask drawable