def render_field
      raise ArgumentError, "Block required" unless block_given?

      @mask.render do
        @mask.clear
        $window.scale 1.0 / @scale do
          yield self
        end
      end

      @shader.enable do
        @field.render do
          @mask.draw 0, 0, 0
        end
      end

      nil
    end
def render_field
      raise ArgumentError, "Block required" unless block_given?

      @mask.render do
        @mask.clear
        $window.scale 1.0 / @scale do
          yield self
        end
      end

      @shader.enable do
        @field.render do
          @mask.draw 0, 0, 0
        end
      end

      nil
    end
Update the SDF should the image have changed.
 Draw the mask in the passed block.