| How to stimulate natural sceneries vividly is always a hot topic and difficult subject in Computer Graphics. The simulation of dynamic natural sceneries, such as fire, rain, cloud and snowflake, are widely used in navigation, spaceflight, movie, advertisement and virtual reality. But the shape of most sceneries in nature changes with time past, and it is difficult to model and visualize these natural sceneries by using traditional methods. So the simulation of natural sceneries is always a hot and difficult research field in Computer Graphics. With the development of research in this subject recently, kinds of simulating algorithms have been proposed, the results of simulating is becoming vivider than before. Among these algorithms, Particle System has been regarded as the most successful one for simulating irregular fuzzy natural sceneries so far.This paper is based on Particle System, and stimulate the irregular natural sceneries like fire rain and rain. At first, we have introduced the basic theories of the Particle System, explained the basic method of structuring mode emphatically. We divided the actual operation of the Particle System into several steps, including Particle attribute establishing, particle producing, particle updating, particle rendering, and explained each operation step indetail; Classified Particle system as particle model system and fluidity model system, interpreted the characteristics of these two kinds of model systems; Have enumerated two examples of Particle System model, the explanation of these two examples accorded to the process above. Showed the operation rules and regulations of each step; Finally paper discussed the graphics technologies of particle rending.Secondly, this paper discusses the method of fire stimulation based on Particle System. It explains the initialization and variation of the fire particles detailedly, including shape, size, color, transparence, position, speed, and so on. It also discusses the motion and rendering of fire particles. It constructs the data structures of Particle Systems and particles by using object-oriented ideas. It designs the functional modules of fire simulation system and divides into four modules; the Particle System module, the particle module, the texture module and the motion field module. In order to enhance the third dimension, we use texture mapping, billboarding and the color mixture techniques for fire rendering. Especially in order to describe the dynamic wavering of fire, for instances, it wavers left and right, up and down, the motion field is introduced into the fire system,we mainly discusses the effect of gravity and wind to the fire. For improving the performance of real time, we use each surface in stead of the dot particle to render the fire particle, so that every surface can substitute hundreds of particles. On the other hand, we use the dynamically generated imposters technique. The speed of implementation is increased. At the end of this passages, we do some research on the methods of improving real time of Particle Systerm.Thirdly, we discuss the simulation methods of other irregular natural sceneries of rain which is based on Particle System simply. After that, we introduce the application of snow Particle System in practice, we also do some research and explain how to improve the real time and give some methods to make up for the compensation. And then, We develop a demo system based on Particle System by using Visual C++ as the programming tools and the three-dimensional animation is supported by OpenGL. This demo system achieve simulating the irregular features which is put forward by the thesis.At last, this paper gives the summary and analysis for the significance of this thesis and the application of research results. And then, do further research on the direction of the thesis and put some forward ideas of the development for this paper. We also do some prospect for the particle system in stimulating irregular features and the application of simulation model for the future in this thesis. At the same time, We introduce the real time and the realistic simulation of Particle System and innovative some ideas to improve them. |
