physics solutions for innovative game design
DESCRIPTION
Give your iPhone games a dynamic real-world feel by integrating a physics engine. This session will give an overview of the current physics engines available for iPhone development, discussing the pros and cons of each. We will also discuss how to decide if a physics engine is right for your project or you are better off with custom code. We'll dive into some real world examples with Ragdoll Blaster which uses the Open Dynamics Engine and talk about optimization, debugging and other tips and tricks.TRANSCRIPT
Physics Solutions for Innovative Game Design
Give your iPhone games a dynamic real-world feel by integrating a physics engine.
Andrei GradinariLead Engineer - Backflip Studios
Tom BlindLead Designer - Backflip Studios
History of Physics in Gamesand
"Physics Games"
History of Physics in GamesVery simple physics (Late 80-s to Early 90-s) - Racing games, flight sims, mini golf games, etc ...
History of Physics in GamesSimple real physics (Middle - Late 90-s) - NFS 1, Unreal, Half-Life, many others
History of Physics in GamesSimple real physics (Middle - Late 90-s) - NFS 1, Unreal, Half-Life, many others
History of Physics in GamesSimple real physics (Middle - Late 90-s) - NFS 1, Unreal, Half-Life, many others
History of Physics in GamesComplex real physics (Early 2000s) - Half-Life 2
History of Physics in GamesComplex real physics (Early 2000s) - Half-Life 2
History of Physics in GamesComplex real physics (Early 2000s) - Half-Life 2
History of Physics in GamesComplex real physics (Early 2000s) - Prey
Prey: Flip Gravity Gameplay Mechanic(how to get to the box with candy)
Prey: Flip Gravity Gameplay Mechanic(how to get to the box with candy)
Prey: Flip Gravity Gameplay Mechanic(how to get to the box with candy)
History of Physics in GamesPhysics on GPUs: Almost real world complexity (Middle to Late 2000's)Crysis engine 3000 Barrels, real time:
History of Physics in GamesPhysics on GPUs: Almost real world complexity (Middle to Late 2000's)
What is a Physics Game?
These are NOT physics gamesEven though they use physics
Doom 3 Unreal
What is a Physics Game?
These are physics games!
Crayon Physics Fantastic Contraption
What is a Physics Game?
Physics EngineDefinition and How It Works
Physics Engine
A physics engine is a set of functions that lets you describe layout of your system of physics objects and then tells you how the state of this system changes over time.
Physics EngineDefine layout of your system of objects (shapes, positions, masses, dimensions, global gravity vector, etc...)
Physics EngineThe engine tells you how your system changes over time
Physics SimulationThe process handled by a physics engine that figures out what happens to the given set of objects over a certain period of time is called physics simulation
->Simulation->
Can be:Not Interactive (user input is not taken in consideration)
Interactive (user input affects the simulation). Interactive simulations are used in most games
Physics Simulation
Do you need a physics engine?
Sometimes, it's easier to do it yourself!
Less memory & CPU usageLess disk spaceLess time spent linking librariesSimpler, if you don't need anything fancy
Do you need a physics engine?
Rolling your own physics:
acceleration = force / massThings get trickier with collisions...
Do you need a physics engine?
The Physics of Paper TossForces are one-dimensional
Add flick force and wind force to determine landing point
Animate to make it look pretty
No physics library needed!
Typical Physics Engine
Consists of:
Rigid Body Dynamics Simulation Engine
Collision Detection Engine
Typical Physics Engine
Building blocks of your physics world:Geometric Shapes (describe what your objects look like)
Joints (describe how your objects are connected to each other)
Typical Physics Engine
Typical Physics Engine
Collision contact points generation (collision detection engine)
Creating temporary joints based on contact points, and attaching them to respective physics objects
Performing actual simulation step (rigid body dynamics engine)
Simulation Step:
Simple Simulation Example (Step 1)
Simple Simulation Example (Step 2)
Simple Simulation Example (Step 3)
Performance Tips and Tricks
Keep things simpleMore objects in your physics simulation = more time spent to simulate the system = lower framerate as a result.
Approximate complex volumes with sets of simple volumes
Performance gain is well worth it.User will never see the difference, as long as you do it right. It's still fine to render fully detailed models, while simulating simple shapes on the physics side.
Performance Tips and Tricks
Example of complex volumes approximation.Rendered models:
Performance Tips and Tricks
Example of complex volumes approximation.Simulated shapes:
Performance Tips and Tricks
Performance Tips and TricksDo not simulate static objects
They should never be simulated in Rigid Bodies Dynamics Engine, because they never move.
Do not simulate dynamic objects that are stationary at the moment.
ODE, for example, automatically does this for you. It is called Auto Disable.
Use spatial partitioning
Setup collision detection engine to generate as few contact points as possible
Several small steps vs one large step
Several small steps:
More realistic simulation, especially when simulating dynamically changing forces
Less problems with objects flying through each other.
One large step:
Less realistic simulation
Better performance
Performance Tips and Tricks
Probable instability problems with simulation and their causes:
Large simulation step
Large forces applied to bodies
Large masses, especially when mixed with small masses
High speeds of the objects
Fast spinning objects
High friction
Performance Tips and Tricks
A Brief Comparison of Physics Engines Used on the iPhone
2DBox2DChipmunk
3DODEBullet
Box2DOptimized for 2D gamesWorks well with cocos2dUsed in many iPhone games such as Crayon Physics and Rolando
Comparison of Physics Engines
ChipmunkVery lightweightWritten in pure CMade by the creators of Crayon Ball for the iPhone"Makes you smarter, stronger, and more attractive to the opposite gender!"
Comparison of Physics Engines
Open Dynamics Engine (ODE)Industry veteranSupports full 3D simulationFast, even on the iPhoneUsed in Touchgrind and Ragdoll Blaster
Comparison of Physics Engines
Bullet Physics LibraryComparison of Physics Engines
Highly optimized for many architecturesMulti-threadedThird most popular physics library according to survey by Game Developer Magazine (Aug. 2009)Used by Oolong Engine (Kids vs. Zombies, iPhysics)
Contemporary physics in games on consoles and PC's = the nearest future of physics in mobile games...
