Mass Spring Particle Systems

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Mass Spring Particle Systems

Contents

This presentation will cover:ObjectivesResearchDesignDevelopmentEvaluation

Stephen Spinks 09012036

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


The Research Phase

The research phase coveredWriting documentsHuman computer interaction (HCI)Mass spring particle systems

Basic concepts Physics Spring networks and their arrangement Collision detection Integration methods Using OpenGL and the GPU


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 = maNo system looks natural unless forces are included (gravity wind,

friction and collisions).The benefits of each force must outweigh it’s computational overheadBasic 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


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


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


The Research Phase: Spring Networks

3 types of spring Structural (stretch) Diagonal (shear) Interleaved (bend)


The Research Phase: Collision Detection

Brief impact stage High velocity decrease

Structural deformation stage Restores original position Disperses energy

Efficiency = realismMain bottleneck of cloth simulation

Point check against all cloth points and environment pointsMethods are available to speed up the process


The Research Phase: Types of Integration

Many small predictions based on the laws of physicsExplicit 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


The Research Phase: Tutorials

Simple set upOne simple collisionGravity includedOpenCloth

OpenGL Utility Toolkit (GLUT) OpenGL Mathematics (GLM)

MoseGaards Cloth Simulation GLUT Textured


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


The Design Phase

Originally a Windows Forms application was designedNot suitable for the projectNext 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


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


The Development Phase

First aims Get application working with the same functionality as OpenCloth Add particle interaction Add text display

Very similar appearanceCode is now OO


The Development Phase: Adding Wind

First improvement was to add windShows this implementation can deal with natural forcesStill looks realisticWorking out the right wind

strength was challengingSimulation and collision can

now be turned on and off


The Development Phase: Adding a Flag

To demonstrate the wind properly a flag was addedA new mesh and an ellipsoid were requiredMust be rectangularIf collision is turned on the

flag can collide with the pole


The Development Phase: Adding Textures

Finally, textures were created and added to theapplication

Different textures were used for the flag andthe cloth

Paul Angel’s texture loading functionwas used

A simple light was addedA normal update function

maps textures correctly


Application Demonstration

Application Demonstration


The Evaluation Phase: Problems Encountered

Main problem – increase in mass when adding particlesSolution – change the weight of each particle so all cloths

weigh the same no matter how many particles in a meshSecond problem – no ability to click and drag particlesSolution – none in available timeThird problem – cloth falling speed too slowPartial solution – increase gravity and modify spring

length (too much gravity = unnatural spring stretch)


The Evaluation Phase: Program Testing

Many different scenarios were used to test the program for errors

Would discover any bugs in the codeA test example

Turn on collision when the cloth isin the middle of the ellipsoid

Expected – cloth jumps back Result – moved back smoother

than expected


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){float deltaTimeMass = deltaTime / mass;size_t i = 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).


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


The Evaluation Phase: Conclusion

Objective 1 – reached, but not as well as expectedObjective 2 – not initially met well, but greatly improvedObjective 3 – achieved as originally imaginedObjective 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


P L E A S E F E E L F R E E T O A S K A N Y Q U E S T I O N S YO U H AV E

Thank you for listening

Mass Spring Particle Systems

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