Sai-Keung Wong

Radial view based culling for continuous self-collision detection of skeletal models

We present a novel radial-view-based culling method for continuous self-collision detection (CSCD) of skeletal models. Our method targets closed triangular meshes used to represent the surface of a model. It can be easily integrated with bounding volume hierarchies (BVHs) and used as the first stage for culling non-colliding triangle pairs. A mesh is decomposed into clusters with respect to a set of observer primitives (i.e., observer points and line segments) on the skeleton of the mesh so that each cluster is associated with an observer primitive. One BVH is then built for each cluster. At the runtime stage, a radial view test is performed from the observer primitive of each cluster to check its collision state. Every pair of clusters is also checked for collisions. We evaluated our method on various models and compared its performance with prior methods. Experimental results show that our method reduces the number of the bounding volume overlapping tests and the number of potentially colliding triangle pairs, thereby improving the overall process of CSCD.

Ice melting simulation with water flow handling

In this paper, we propose a new approach based on a particle-based model for ice melting simulation. Each particle has an attribute called virtual water. The amount of the virtual water of an ice particle indicates the amount of water surrounding the ice particle. The transfer of the virtual water is performed between the exterior ice particles so as to simulate the thin layer of water flow on the surface. Our approach also handles the transition between the virtual water and the water particles. We compute the isosurface of a density field defined by the ice particles and the virtual water. A simple ray tracing method is adopted for rendering the objects. We report the experimental results of several ice melting simulations with water flow and water drops.

Guidance path scheduling using particle swarm optimization in crowd simulation

In this paper, we propose a method for using particle swarm optimization (PSO) to compute optimal guidance paths for various crowd densities in an agent‐based crowd simulation. The inputs of our system are guidance paths that provide hints for the movement directions of agents. Input guidance paths may not be located correctly (e.g., leading to congestion or high traveling cost); therefore, our method adjusts the guidance paths by using PSO. We consider several factors for evaluating the quality of a guidance path, including the average traveling time and interaction distance between agents. We apply our method in several examples. Experimental results show that our method can compute adaptive guidance paths for various crowd densities. Our system can simulate organized crowds that move in directions specified by the guidance paths. Copyright

Dynamic radial view based culling for continuous self-collision detection

The radial view-based culling (RVBC) method has been presented for continuous self-collision detection to efficiently cull away non-colliding regions. While this technique mainly relies on the segmented clusters of the reference pose and the associated fixed observer points, it has several drawbacks during the animation and the reduced cost of executing collision detection is limited. We thus present a modified framework to improve the culling efficiency of RVBC. At the preprocessing stage, we segment the closed deformable mesh according to not only the attached skeleton but also the triangle orientations, in order to minimize the collision checks of triangles in a cluster. At the runtime stage, we dynamically merge adjacent clusters and update the positions of observer points if the merged shape is nearly convex. This strategy minimizes the number of triangles in different clusters that required collision check. Our framework can be easily integrated with bounding volume hierarchies to boost the culling efficiency. Experimental results show that our framework achieves up to 5.2 times speedup over the original RVBC method and even more times over the recent techniques.

Game team balancing by using particle swarm optimization

Game balancing affects the gaming experience of players in video-games. In this paper, we propose a novel system, team ability balancing system (TABS), which is developed for automatically evaluating the performance of two teams in a role-playing video game. TABS can be used for assisting game designers to improve team balance. In TABS, artificial neural network (ANN) controllers learn to play the game in an unsupervised manner and they are evolved by using particle swarm optimization. The ANN controllers control characters of the two teams to fight with each other. An evaluation method is proposed to evaluate the performance of the two teams. Based on the evaluation results, the game designers can adjust the abilities of the characters so as to achieve team balance. We demonstrate TABS for our in-house MagePowerCraft game in which each team consists of up to three characters.

Continuous collision detection for deformable objects using permissible clusters

In this paper, we propose a new data structure to perform continuous collision detection (CCD) for deformable triangular meshes. The critical component of this data structure is permissible clusters. At the preprocessing phase, the triangular meshes are divided into permissible clusters. Then, the features of the triangular meshes are assigned to the permissible clusters. At the runtime phase, the potentially colliding feature pairs are collected and they are processed only once in the elementary processing. Our method has been integrated with a normal cone-based method and compared with other CCD methods. Experimental results show that our method improves the overall performance of CCD for deformable objects.

Interactive Sand Art Drawing Using Kinect

In this paper, we present an interactive sand art drawing system using Kinect. Our system adopts a vision-based bare hand detection method which effectively detects the hand position and recognizes the hand gestures. Then, the corresponding sand manipulation actions are performed. Our system supports the common sand drawing functions, such as sand erosion, sand sand spilling, and sand leaking. To use hands to draw virtual sand on a drawing plane, we design four key gestures which enable drawing manipulation actions for sand. The basic idea is that the gesture of one hand controls the drawing action. The motion and gesture of the other hand controls the drawing position. Our preliminary experimental results show that our system enables sand drawing with bare hands using Kinect. A user study indicates our system is useful to sand art drawing.

Continuous Self-Collision Detection for Deformable Surfaces Interacting with Solid Models

In this paper, we propose a new continuous self‐collision detection (CSCD) method for a deformable surface that interacts with a simple solid model. The method is developed based on the radial‐view‐based culling method. Our method is suitable for the deformable surface that has large contact region with the solid model. The deformable surface may consist of small round‐shaped holes. At the pre‐processing stage, the holes of the deformable surface are filled with ghost triangles so as to make the mesh of the deformable surface watertight. An observer primitive (i.e. a point or a line segment) is computed so that it lies inside the solid model. At the runtime stage, the orientations of triangles with respect to the observer primitive are evaluated. The collision status of the deformable surface is then determined. We evaluated our method for several animations including virtual garments. Experimental results show that our method improves the process of CSCD.

Technical Section: A heuristic approach to the simulation of water drops and flows on glass panes

Water drops and water flows exhibit interesting motion behavior. In this paper, we adopt a simple but effective approach for simulating this behavior on glass panes in a physically plausible manner. We combine a particle system and a height map to compute their movements and shapes. Our approach efficiently handles the merging of water drops and the formation of residual water droplets. We report our results for several examples of water behavior simulated in real time. The experimental results show that our system simulates water drops and water flows with high quality.

A hybrid method for water droplet simulation

In this paper, we propose a hybrid method for simulating water droplets on the glass pane. We model the motion of water droplets based on a particle system. The shape of the water droplets is constructed by converting the particles into a height map according to the water amount of the water droplets. To realistically compute the shape of the water droplets, we also consider their movement directions when the height map is computed. We have implemented our system and evaluated its performance. Our system can simulate the water droplets realistically at an interactive rate.