Abstract: Rendering high quality shadows with large penumbra in real-time is a challenging problem.In this paper,we propose a new edge extracting method with a new data structure to attack this problem and provide an efficient and practical technique for soft shadow generation.First,a multi-pass method to fit edge lines in a fixed size block containing edge pixels is presented,and then a hierarchical texture map saving these lines entitled hierarchical edge map(HEM) is employed.Finally the visibility is computed by back-projecting these lines in HEM onto the 2D light source domain to generate realistic soft shadow.The rendering performance is greatly improved,while keeping the soft shadow quality.