Abstract: We present a fast GPU-based method for rendering boundary surfaces from dynamic 3D particle clouds. Instead of extracting and tracking polygonal meshes of boundary surfaces in 3D world space, we devise a new meshless 2D screen-space approach. First, we generate a smooth view-dependent depth map from the 3D particle cloud. Then, surface normals are derived directly from the depth map, and lighting calculations are carried out in screen space. The advantage of our method over existing rendering approaches for particle-based objects is the fact that we do not have to extract 3D or 2D meshes at any time. We focus on free surfaces of 3D particle-based, interactive liquid simulations. Thus, we extend the basic algorithm with efficient reflection and refraction approximations.