code: def _linepoint(self, t, x0, y0, x1, y1):
          
          # Originally from nodebox-gl
          out_x = x0 + t * (x1 - x0)
          out_y = y0 + t * (y1 - y0)
          return (out_x, out_y)
docs: Returns coordinates for point at t on the line.
              Calculates the coordinates of x and y for a point at t on a straight line.
              The t parameter is a number between 0.0 and 1.0,
              x0 and y0 define the starting point of the line,
              x1 and y1 the ending point of the line.