code: private static Shader createRadialGradient(@NonNull final Orientation orientation,
                                                 final int bitmapSize, final float radius) {
          PointF center = new PointF();
  
          switch (orientation) {
              case TOP_LEFT:
                  center.x = bitmapSize;
                  center.y = bitmapSize;
                  break;
              case TOP_RIGHT:
                  center.y = bitmapSize;
                  break;
              case BOTTOM_LEFT:
                  center.x = bitmapSize;
                  break;
              case BOTTOM_RIGHT:
                  break;
              default:
                  throw new IllegalArgumentException("Invalid orientation: " + orientation);
          }
  
          return new RadialGradient(center.x, center.y, radius, Color.TRANSPARENT, Color.BLACK,
                  Shader.TileMode.CLAMP);
      }
docs: Creates and returns a shader, which can be used to draw a shadow, which located at a corner
  of an elevated view.
  
  @param orientation
  The orientation of the shadow in relation to the elevated view as a value of the enum
  {@link Orientation}. The orientation may either be <code>TOP_LEFT</code>,
  <code>TOP_RIGHT</code>, <code>BOTTOM_LEFT</code> or <code>BOTTOM_RIGHT</code>
  @param bitmapSize
  The size of the bitmap, which is used to draw the shadow, in pixels as an {@link
  Integer} value
  @param radius
  The radius, which should be used to draw the shadow, in pixels as a {@link Float}
  value
  @return The shader, which has been created as an instance of the class {@link Shader}