13_3dgp_gamephyics

8/7/2019 13_3DGP_GamePhyics

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Game PhysicsGame Physics


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Tr aditional game physicsTr aditional game physics

Pa r ticle systemPa r ticle system Rigid body dynamicsRigid body dynamics Flexible body dynamicsFlexible body dynamics

Some stateSome state- -ofof--a r t topicsa r t topics

Ca r physicsCar physics Fluid dynamicsFluid dynamics RagRag--doll physicsdoll physicsPhysicsPhysics

Rigid body kinematicsRigid body kinematics Newtons LawsNewtons Laws Fo rcesForces MomentaMomenta Ene rgyEne rgy

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Introduction to Game PhysicsIntroduction to Game Physics


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Newtons LawsNewtons Laws

11stst

LawLaw

22ndnd LawLaw F = ma = mF = ma = m HHv/v/ HHtt

33rdrd

LawLaw

ForcesForces G rav ity / Spr ing fo rces / Fr iction / ViscosityGrav ity / Spr ing fo rces / Fr iction / Viscosity

Torq ueTorq ue XX = r X F= r X F

Equilib r iumEquilib r ium

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B asic Concepts from Physics (1/2)B asic Concepts from Physics (1/2)


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MomentaMomenta

Linea r momentumLinea r momentum Angula r momentumAngula r momentum Moment of ine r tiaMoment of ine r tia

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B asic Concepts from Physics (2/2)B asic Concepts from Physics (2/2)


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Pa r ticles a re objects withPa r ticles a re objects with

MassMass PositionPosition VelocityVelocity

Respond to fo rcesRespond to fo rcesBBut no spatial extent (no size!)ut no spatial extent (no size!)

Point massPoint mass

BBased on Newton Lawsased on Newton Laws f f = m= m aa x x == f f / m/ m v v == f f / m,/ m, x x == vv

Particle DynamicsParticle Dynamics

..

. .


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typedef struct {

float m; /* mass */float *x; /* position */float *v; /* velocity */float *f; /* force accumulator */

} *Particle;

typedef struct {Particle *p /* array of pointers to particles */int n; /* number of particles */float t; /* simulation clock */

} *ParticleSystem;

x

v

f m

states

x

v

f

m

x

v

f

m

x

v

f

m

x

v

f

m

x

v

f

m

P article n time

B asic Particle SystemB asic Particle System


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/* gather states from the particles */void ParticleGetState(ParticleSystem p, float *dst){

int i;for (i = 0; i < p->n; i++) {

*(dst++) = p->p[i]->x[0];*(dst++) = p->p[i]->x[1];*(dst++) = p->p[i]->x[2];*(dst++) = p->p[i]->v[0];*(dst++) = p->p[i]->v[1];*(dst++) = p->p[i]->v[2];

}}


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/* scatter states into the particles */void ParticleSetState(ParticleSystem p, float *src){

int i;for (i = 0; i < p->n; i++) {

p->p[i]->x[0] = *(src++);p->p[i]->x[1] = *(src++);p->p[i]->x[2] = *(src++);p->p[i]->v[0] = *(src++);p->p[i]->v[1] = *(src++);p->p[i]->v[2] = *(src++);

}}


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/* calculate derivative, place in dst */void ParticleDerivative(ParticleSystem p, float *dst){

int i;

ClearForce(p);ComputeForce(p);

for (i = 0; i < p->n; i++) {*(dst++) = p->p[i]->v[0];*(dst++) = p->p[i]->v[1];*(dst++) = p->p[i]->v[2];*(dst++) = p->p[i]->f[0]/p->p[i]->m;*(dst++) = p->p[i]->f[1]/p->p[i]->m;

*(dst++) = p->p[i]->f[2]/p->p[i]->m;}

}


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/* Euler Solver */void EulerStep(ParticleSystem p, float DeltaT){

ParticleDeriv(p, temp1);ScaleVector(temp1, DeltaT);ParticleGetState(p, temp2);AddVector(temp1, temp2, temp2);ParticleSetState(p, temp2);p->t += DeltaT;

}


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Mass of a BodyMass of a Body

Mass cente rMass cente rForceForce Linea r momentumLinea r momentum P(t) = M v (t)P(t) = M v (t)

Velocity (Velocity ( v v ))Torq ueTorq ue Angula r momentumAngula r momentum L(t) = IL(t) = I [ [ (t)(t) Local rotation (Local rotation ( [ [ ))

Ine r tia Tenso rIne r tia Tenso rRefe renceRefe rence wwwwww--2 . cs . cmu . edu / afs / cs / use r / ba raff / www / pbm2. cs . cmu . edu / afs / cs / use r / ba raff / www / pbm 11

R igid B ody DynamicsR igid B ody Dynamics


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Spr ingSpr ing--mass modelmass model

F = k x F = k x Not a st ressNot a st ress--st rain modelst rain model Lack of Elasticity, Plasticity, & ViscousLack of Elasticity, Plasticity, & Viscous- -ElasticityElasticity Can be unstableCan be unstable

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F lexible B ody Dynamics (1/2)F lexible B ody Dynamics (1/2)


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F lexible B ody Dynamics (2/2)F lexible B ody Dynamics (2/2)

Finite element methodFinite element method

(( )) Sol v e r fo r ODE/ PDESolv e r fo r ODE/ PDE Bounda ry conditionsBounda ry conditions Ene rgy e quationEne rgy e quation

St ressSt ress--st rain modelst rain model Ve ry complicated computing p rocessVery complicated computing p rocess

Conse rv ation of ene rgyConse rv ation of ene rgy


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A dvanced Topics in Game PhysicsA dvanced Topics in Game Physics

Fractu re Mechanics (Fractu re Mechanics ( ))

Fluid Dynamics (Fluid Dynamics ( ))Car Dynamics (Car Dynamics ( ))RagRag--doll Physics (doll Physics ( ))


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Game FXGame FX


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Imp rov e the Visual & Sound Game EffectsImp rov e the Visual & Sound Game Effects

IncludesIncludes Combat FXCombat FX En v ironment FXEnv ironment FX Cha racte r FXCha racte r FX Scene FXScene FX Sound FXSound FX

FX Edito r NeededFX Edito r Needed Gene ral 3D animation tools can not do itGene ral 3D animation tools can not do it

KeyKey--f rame system is not wo rkingframe system is not wo rking FX animation is alwaysFX animation is always

Procedu rallyProcedu rallyRelated to the p re v ious f rameRelated to the p re v ious f rame

Small Wo rk But La rge EffectSmall Wo rk But La rge Effect16

Introduction to Game FXIntroduction to Game FX


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FX Editing ToolFX Editing Tool


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Game Particle EffectsGame Particle Effects

Conque r Online


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Dur ing the CombatDur ing the Combat

Weapon motion blu rWeapon motion blu r Weapon effectWeapon effect Skill effectSkill effect

Afte r the CombatAfte r the Combat Damage effectDamage effect

FX Edito rFX Edito r

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Combat FXCombat FX


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Compute r Animation :Compute r Animation :

Image solutionImage solution Blending rende red image se quenceBlending rende red image se quence

Rende r too many f ramesRende r too many f rames Div ide the f ramesDiv ide the f rames Av e rageAv e rage Done!Done!

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M otion B lurM otion B lur Image SolutionImage Solution


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In Games, Use Tr anspa rent Objects to Simulate theIn Games, Use Tr anspa rent Objects to Simulate the

Motion Blu rMotion Blu rFalse Motion Blu rFalse Motion Blu r Tr acking the motion path of the objectTr acking the motion path of the object Connecting them as a t r iangula r meshConnecting them as a t r iangula r mesh

Use timeUse time- -dependent semidependent semi- -t ranspa rency to simulate thet ranspa rency to simulate theblu rblu r

The path can be smoothed using CatmullThe path can be smoothed using Catmull- -Rom splineRom spline Local stability of the cu rv eLocal stability of the cu rv e

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M otion B lurM otion B lur Geometry SolutionGeometry Solution


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Almost All Game FXs Use this Tr ickAlmost All Game FXs Use this Tr ick

Geomet ry Object on which the Textu re AnimationGeomet ry Object on which the Textu re AnimationPlayingPlaying Billboa rdBillboa rd 3D Plate3D Plate Cylinde rCylinde r Sphe reSphe re Re v olv ing a c ross section cu rv eRev olv ing a c ross section cu rv e

Textu re Se quence with Colo rTextu re Se quence with Colo r--keykey

SemiSemi--t ranspa rent Textu rest ranspa rent Textu res Alpha blendingAlpha blending Sou rce colo r added to backg roundSource colo r added to backg round

Demo!!!!Demo!!!!23

FX Uses Texture A nimationFX Uses Texture A nimation


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The FXsThe FXs Fi re / exposu re / smoke / dustFire / exposu re / smoke / dust

Initial Value + Time dependencyInitial Value + Time dependencyCombined with Billboa rd FXCombined with Billboa rd FX Billboa rd to play the textu re animationBillboa rd to play the textu re animation

Pa r ticle system to calculate the motion pathPa r ticle system to calculate the motion pathGra v ity is the majo r fo rce usedGra v ity is the majo r fo rce usedEmitte r patte rnEmitte r patte rn Single emitte rSingle emitte r

Area emitte rArea emitte r Emitte r on v e r ticesEmitte r on v e r tices

Demo !!!Demo !!!24

Particle System for FX s in CombatParticle System for FX s in Combat


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Weathe rWeathe r

Use pa r ticle systemUse pa r ticle system RainRain SnowSnow WindWind

FogFog Tr aditional fogTr aditional fog

F rom nea r to fa rFrom nea r to fa r Ha rdwa re standa rd featu reHardwa re standa rd featu re

Volume fogVolume fog Laye red fogLaye red fog Use v e r tex shade rUse v e r tex shade r

Day & NightDay & Night

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Environment FXEnvironment FX


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FatalityFatality

Case by case and need c reati v e solutionsCase by case and need c reati v e solutionsRende r ing Effects on SkinsRende r ing Effects on Skins En v ironment mappingEnv ironment mapping Bump mapBump map

No rmal mapNormal map Multiple textu re mapMultiple textu re map

Flexible bodyFlexible body Flexible body dynamicsFlexible body dynamics

FurFur RealReal--time fu r rende r ingtime fu r rende r ing

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Character FXCharacter FX


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Use a v e ry la rge box o r domeUse a v e ry la rge box o r dome--like model to su rr oundlike model to su rr oundthe whole game scenethe whole game scene

Use textu res on the box o r dome as the backd ropUse textu res on the box o r dome as the backd ropUse multiple textu res and textu re coo rdinatesUse multiple textu res and textu re coo rdinatesanimation to simulate the mo v ing of the cloudsanimation to simulate the mo v ing of the clouds

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Scene FX Scene FX Sky B oxSky B ox


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Runtime calculate the position and o r ientation ofRuntime calculate the position and o r ientation of

the came ra with the sunthe came ra with the sunPut textu res to simulate the lens fla rePut textu res to simulate the lens fla re

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Scene FX Scene FX Lens F lareLens F lare


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Atmosphe r ic light scatte r ingAtmosphe r ic light scatte r ing

Caused by dust, molecules, o r wate r v apo rCaused by dust, molecules, o r wate r v apo r These can cause light to be:These can cause light to be:

Scatte red into the line of sightScatte red into the line of sight (in(in--scatte r ing)scatte r ing) Scatte red out of the line of sightScatte red out of the line of sight (out(out--scatte r ing)scatte r ing) Abso rbed altogethe r Absorbed altogethe r (abso rption)(abso rption)

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Scene FX Scene FX Light ScatteringLight Scattering

Skylight and sun lightSkylight and sun lightCan be Implemented by v e r texCan be Implemented by v e r tex shade rshade r


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Scene FX Scene FX Light Scattering ExamplesLight Scattering Examples

With scatte r ingWithout scatte r ing


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OGRE Particle SystemOGRE Particle System

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OGRE Par ticle System Att r ibuteshttp: // www . ogre3d . org/ docs / manual / manual_32 . html

OGRE Par ticle Edito rhttp: // www . game-cat . com / ogre / pe / Pa r ticleEdito r_Beta . zip

OGRE Par ticle Edito r Tuto r ialhttp: // www . game-cat . com / ogre / pe / docs / PETuto r ial . htm


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Particle System DefinitionParticle System Definition

Attributes (Partial)Attributes (Partial)

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Attribute Name Value Format Description

quota Maximum number of particles at one time in thesystem (default 10 ).

material Name of material used by all particles in thesystem (default none).

particle_width Width of particles in world coordinates (default100 ).

particle_height Height of particles in world coordinates (default100 ).

cull_each | Cull particles individually (default false).

sorted | Sort particles by depth from camera (default false).

billboard_type | | |

Billboard-renderer-specific attribute (defaultpoint).

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