Physically Based Animation Intro

10/1/2009 John Dingliana • Graphics Vision Visualization Group • Computer Science Department CS7057 Real-time Physics • Lloyd 041 ::: [email protected] Course Overview • My areas of interest: – Level-of-detail in real-time Physically Based Animation – Visualization – Interaction – Non-photorealistic Animation and Rendering Graphics Vision and Visualisation (gv2) GV2 Graphics Lab • GV2 research group: • Some Research Areas of – Image synthesis group relevance to this 1993 (graphics) course: – Computer vision and – Physically based robotics group 1983 animation – Crowd animation – Perception of graphics and animation – Urban simulation – Fluid animation Sensics Pi- Sight HMD – Motion capture Course Pre-requisites Assessment • CS7033 Real-time Animation • 100% by coursework • Recommended: • Aggregate mark of 40% is required to pass – C++, C# or equivalent • – Computer Graphics (3D Graphics) Coursework: – Regular small lab assignments • Some experience in OpenGL or 3D Graphics Library • Bi-weekly • Undergraduate maths (some basics reviewed) – One major assignment (linked with CS7033) • Both parts of the course • Supplemental is by EXAM (for PGDip only) 1 10/1/2009 MODULE Web Page Aims • Course Notes + Updates • Outline and describe the architecture and components of a motion pipeline that would be employed in a typical game. – http://www.scss.tcd.ie/John.Dingliana/cs7057/ • Explain basic rigid body dynamics and the mechanics of – Access to notes will requires log in with Compsci deformable systems. username + password • Analyze and compare different approaches for collision detection and collision response of rigid and deformable objects. • Employ existing Physics libraries to create real-time physics based simulations of rigid and deformable bodies • Be able to build a real-time rigid body simulation system for convex polyhedra. Specific Themes Relevant References • Topics chosen from but not limited to: • Baraff, Witkin and Kass “Physically based Animation Course notes” – Siggraph 2001 – Particle System Dynamics – http://www.pixar.com/companyinfo/research/pbm2001/ – 3D Rigid Body Dynamics • Mueller, James, Theurey, Stam “Real-time Physics” – – Collision detection for polyhedral objects Siggraph 2008 • Multi-phase collision detection – http://www.matthiasmueller.info/realtimephysics/index.html • Bounding Volume Hierarchies • Narrow Phase Collision Detection » Kenny Erleben - “Physics based animation” – Multiple Contact resolution » David H.Eberley“Game Physics Engine – Deformable objects + Cloth simulation Development” – Fluid simulation (overview) Real-time Physics Physically Based Modelling • Increasingly important topic in past decade • A form of Procedural Modelling, • Behavioral animation -> • Popular Physics Engines: animate behaviour • Physics -> inanimate motions due to external forces • Also common in 3D modelling/animation tools: MAX(havok reactor), Blender(bullet) • Motivations: Realism / plausibility, Useful Automation , Interaction 2 10/1/2009 State of the Art Physics • Havok • Natural Motion - Euphoria • Pixelux - DMM (c) Irving, Shroeder and Fedkiw 2007 Concerns Application Areas • Efficiency • Virtual reality • Interactive computer • Fidelity or complexity animation • Surgical simulation; • Realism or plausibility preoperative planning • Robustness • Computational robotics; manipulation • Video games • Assembly planning • Scientific visualization • Education Physically Based Animation Collision Handling • Kinematics • The basis for interaction – The study of motion without considering mass or – Object – object interaction forces – • Dynamics User – object interaction – The study of motion taking into account mass and • Three phases: forces – Collision detection – Inverse Dynamics: the study of motion given the start – Contact modelling and end points – Forward Dynamics: the study of motion given only the – Collision response, contact resolution start points – most important for interactive apps 3 10/1/2009 Collision Detection Collision Detection Sphere-sphere Sphere-plane Polygon-polygon Triangle-Triangle Lots of Intersection Source Code Available Here: Intersection testing and collision detection http://www.geometrictools.com/LibFoundation/Intersection/Intersection.html Problem Over-approximation Problems Display Meshes are generally Possible solution: Use a simplified more detailed than we wish to representation. (Even this is deal with for collision detection. generally overkill for a game) Hit Boxes Collision Proxies Rag-doll collision proxy for character. http://www.havok.com/misc/physicsEfficiency-2007.pdf 4 10/1/2009 Bounding Volumes Bounding Volume Hierarchies Levels of AABB Tree Hierarchy Two Phase Collision Detection Collision Response • Broad phase • Collision Response Concerns: – Impulses: instantaneous change in velocity – Per-object : coarse culling of non-colliding cases – Resting contact – Constraints • Narrow phase – Friction • Key Concerns in Interactive Physics: – Pair-wise between objects – Robustness: response must assure system remains – Per-feature stable in all possible states – Narrow-in on collision – calculate finer features – Plausibility: response to collision must be believable e.g. collision manifold, penetration depth – Efficiency: physics processing must be fast enough to enable real-time frame rates Deformable Objects Upcoming topics in this module • Problems: • Overview of Physics in Computer Animation • Particle Simulation – How should objects deform: • Numerical Integration of ODE's for Simulation • Realism • • Robustness/stability Rigid Body Dynamics – Collision Detection (several lectures) • Efficiency – Contact Modelling – Collision detection – Collision Response • Bounding volumes no longer valid • Multi-body Simulation Issues • Pre-processing short cuts no longer possible • Deformable Objects and Cloth • Collision proxies need to be updated – Cartoon Physics – Behaviours: • Bullet Physics Engine • Moments of inertia • Fluid Simulation 5.

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