def _draw_frozen_pattern(self):
        """Draws frozen pattern, i.e. diagonal lines"""

        self.context.save()

        x, y, w, h = self.rect
        self.context.set_source_rgb(0, 0, 1)
        self.context.set_line_width(0.25)
        self.context.rectangle(*self.rect)
        self.context.clip()

        for __x in numpy.arange(x-h, x+w, 5):
            self.context.move_to(__x, y + h)
            self.context.line_to(__x + h, y)
        self.context.stroke()

        self.context.restore()
Draws frozen pattern, i.e. diagonal lines