1. A rendering method for reducing complexity comprising: obtaining information about a sightline of a user; determining rendering quality based on the obtained information; and rendering a graphic image according to the determined rendering quality, wherein the rendering quality denotes a level-of-detail of the graphic image displayed on a screen, wherein the graphic image is newly rendered for reducing complexity when the determined rendering quality is lower than previous rendering quality, wherein the obtaining of the information about the sightline of the user comprises obtaining a distance from the user to the screen that displays the graphic image and an angle between a direction of the sightline of the user and a direction of a normal line of the screen, and wherein the rendering quality is determined based on a reciprocal of the obtained distance and a reciprocal of the obtained angle.