Class: DropShadow

Configuration for drop shadow. It can have these
attributes:

• angle {int} The direction toward which the shadow is cast
  (in degrees: [0, 360], clockwise). The default value is 45.


• color {String} The color of the shadow. The string format is "#RRGGBB"


• knockout {Boolean} If knockout is true, then the object to which the shadow
  effect is applied knocks out the shadow where it overlaps, allowing the
  background to show through.


• offset {float} The offset between the casted shadow and the object (in pixels).
  The value should be a positive value. Default value is 2.


• opacity {float} The opacity of the shadow. A number between 0 and 1.
  Default value is 0.5


• radius {float} Defines how hazy, or how blurry, the drop shadow is.
  Default value is 2.


• applyToLayer {boolean} When true, the filter is applied to the layer as a
  whole. When false, the filter is applied to the individual features. Default is true.