Adaptive quadtree subdividing contour plotting algorithms

Two simple and efficient contour plotting algorithms are presented. The first algorithm is a colour-fill algorithm. The second algorithm is a colour-fill algorithm as well as a contour line plotting algorithm. Using adaptive quadtree subdividing and linear interpolation, both algorithms are easy to implement. In addition, the contour plotting for a given mesh can be performed parallelly since plotting the contour of an element is totally independent of any other element.