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Mass Spring Particle Systems

Mass Spring Particle Systems. Stephen Spinks 09012036. Contents. This presentation will cover: Objectives Research Design Development Evaluation. Stephen Spinks 09012036. Objectives. To research, identify and compare a variety of mass spring particle systems

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Mass Spring Particle Systems

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  1. Mass Spring Particle Systems

    Stephen Spinks 09012036
  2. Contents This presentation will cover: Objectives Research Design Development Evaluation Stephen Spinks 09012036
  3. Objectives To research, identify and compare a variety of mass spring particle systems To design different methods of creating mass spring particle systems and an application to demonstrate them To develop an application to demonstrate different mass spring particle systems To evaluate the quality, and realistic appearance of the mass spring particle systems and the application used to demonstrate them Stephen Spinks 09012036
  4. The Research Phase The research phase covered Writing documents Human computer interaction (HCI) Mass spring particle systems Basic concepts Physics Spring networks and their arrangement Collision detection Integration methods Using OpenGL and the GPU Stephen Spinks 09012036
  5. The Research Phase: Basic Concepts A modelling system contains a set of modelling elements (particles) A particle contains both static and dynamic states, which will evolve over time using f = ma No system looks natural unless forces are included (gravity wind, friction and collisions). The benefits of each force must outweigh it’s computational overhead Basic simulation loop: Reset the modelling system Set the acceleration for each particle, using the force Move the system forward by one time step Check for and handle any collisions Display the results to the screen Stephen Spinks 09012036
  6. The Research Phase: Physics Gravity Acts downwards f = mg 9.81 (2 d.p.) Hooke’s Law Determines the force on two masses, connected by a spring Rest length = no force in either direction Stephen Spinks 09012036
  7. The Research Phase: Physics Provot Dynamic Inverse Many high stresses in a small area produce unrealistic characteristics Possible solutions Increase stiffness Use dynamic inverse procedures Xavier Provot’s algorithm Compare current length to rest length Move non-fixed ends towards each other Helps deformation move through the cloth Stephen Spinks 09012036
  8. The Research Phase: Spring Networks 3 types of spring Structural (stretch) Diagonal (shear) Interleaved (bend) Stephen Spinks 09012036
  9. The Research Phase: Collision Detection Brief impact stage High velocity decrease Structural deformation stage Restores original position Disperses energy Efficiency = realism Main bottleneck of cloth simulation Point check against all cloth points and environment points Methods are available to speed up the process Stephen Spinks 09012036
  10. The Research Phase: Types of Integration Many small predictions based on the laws of physics Explicit Euler Simplest form of integration Least processor heavy Add position and velocity change Less accurate than RK4 Runge-Kutta Order 4 (RK4) Very processor intensive Detects rate of change any times every timestep Combined to create an average Stephen Spinks 09012036
  11. The Research Phase: Tutorials Simple set up One simple collision Gravity included OpenCloth OpenGL Utility Toolkit (GLUT) OpenGL Mathematics (GLM) MoseGaards Cloth Simulation GLUT Textured Stephen Spinks 09012036
  12. The Research Phase: Outputs Chosen language: C++ and OpenGL using Visual Studio 2010 Physics to include Hooke’s Law Drag Gravity Cloth layout: Using all three spring types Stretch Shear Bend Stephen Spinks 09012036
  13. The Design Phase Originally a Windows Forms application was designed Not suitable for the project Next idea Build on top of OpenCloth but, All in one source file Uses freeglut New idea Use OO code Setup OpenGL with Paul’s code Use Paul’s CGFont class to display text Stephen Spinks 09012036
  14. The Design Phase Extra functionality to include: Add text to the screen Increase the number of cloth particles in real-time Add wind Add collision Add texture to the cloth Stephen Spinks 09012036
  15. The Development Phase First aims Get application working with the same functionality as OpenCloth Add particle interaction Add text display Very similar appearance Code is now OO Stephen Spinks 09012036
  16. The Development Phase: Adding Wind First improvement was to add wind Shows this implementation can deal with natural forces Still looks realistic Working out the right wind strength was challenging Simulation and collision can now be turned on and off Stephen Spinks 09012036
  17. The Development Phase: Adding a Flag To demonstrate the wind properly a flag was added A new mesh and an ellipsoid were required Must be rectangular If collision is turned on the flag can collide with the pole Stephen Spinks 09012036
  18. The Development Phase: Adding Textures Finally, textures were created and added to the application Different textures were used for the flag and the cloth Paul Angel’s texture loading function was used A simple light was added A normal update function maps textures correctly Stephen Spinks 09012036
  19. Application Demonstration Application Demonstration Stephen Spinks 09012036
  20. The Evaluation Phase: Problems Encountered Main problem – increase in mass when adding particles Solution – change the weight of each particle so all cloths weigh the same no matter how many particles in a mesh Second problem – no ability to click and drag particles Solution – none in available time Third problem – cloth falling speed too slow Partial solution – increase gravity and modify spring length (too much gravity = unnatural spring stretch) Stephen Spinks 09012036
  21. The Evaluation Phase: Program Testing Many different scenarios were used to test the program for errors Would discover any bugs in the code A test example Turn on collision when the cloth is in the middle of the ellipsoid Expected – cloth jumps back Result – moved back smoother than expected Stephen Spinks 09012036
  22. The Evaluation Phase: Big O Notation Big O notation describes the performance of an algorithm, It uses the worst case scenario void Physics::IntegrateEuler(void){ floatdeltaTimeMass = deltaTime / mass; size_ti = 0; for(i = 0; i < totalParticles; i++) { glm::vec3 oldV = (*V)[i]; (*V)[i] += ((*F)[i] * deltaTimeMass); (*X)[i] += deltaTime * oldV; if((*X)[i].y < 0) (*X)[i].y = 0; } } Resulting notation – O(N). Stephen Spinks 09012036
  23. The Evaluation Phase: Future Enhancements Particle manipulation Place the cloth in any position See how it would react Use the GPU Demonstrate the advantage of GPU usage Allow the cloth to fall more naturally Self collision Most complex enhancement Add extra realism Very computationally expensive Stephen Spinks 09012036
  24. The Evaluation Phase: Conclusion Objective 1 – reached, but not as well as expected Objective 2 – not initially met well, but greatly improved Objective 3 – achieved as originally imagined Objective 4 – achieved as predicted There were some hiccups along the way, but it has turned out as expected and met the original objectives to a good level Stephen Spinks 09012036

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