Implementation of an Implementation of an Outdoor Shooting GameOutdoor Shooting Game

Szirmay-Kalos LászlóBudapest University of Technology

email: szirmay@iit.bme.huWeb: http://www.iit.bme.hu/~szirmay

Demo 1: The objectiveDemo 1: The objective

Virtual realityVirtual realityVirtual world

avatar

Userinput

rendering interaction

Tasks in gamesTasks in games

Image synthesis from the point of view of the avatar

Control of the avatar through input devices (keyboard, mouse)

Control of the intelligent virtual objects by artificial intelligence algorithms

Simulation of the physical laws (collisions, forces)

I/O librariesI/O libraries

rendering

Virtual world

input

simulation

OpenGL

Windows + GLUT

I/O managementI/O management

OperatingSystem

WindowsGLUT

main

DisplayFunc

KeyboadFunc

IdleFunc

OpenGLGraphicshardware

application

initializationcallback registration

callbacksSpecialFunc

Rendering with OpenGLRendering with OpenGL

Virtual world Viewing transformation

Perspectivetransformation

1325628 1325628

1.2.

clipping visibility: z-buffer display

Geometry definitionGeometry definitionglBegin(GL_TRIANGLES);

glColor3f( 1, 1, 0 ); glVertex3f( x11, y11, z11 );glVertex3f( x12, y12, z12 );glVertex3f( x13, y13, z13 );

glColor3f( 0, 1, 0 ); glVertex3f( x21, y21, z21 );glVertex3f( x22, y22, z22 );glVertex3f( x23, y23, z23 );

glEnd();

x11,y11,z11

x12,y12,z12

x13,y13,z13

glColor4f(R,G,B,A)

TexturingTexturing

Texture mappingTexture mapping

glEnable(GL_TEXTURE_2D);glBindTexture(GL_TEXTURE_2D, texture_id); // which textureglBegin(GL_TRIANGLES);glTexCoord2f(u1, v1); glVertex3f(x1, y1, z1);glTexCoord2f(u2, v2); glVertex3f(x2, y2, z2);glTexCoord2f(u3, v3); glVertex3f(x3, y3, z3);glEnd();glDisable(GL_TEXTURE_2D);

(u1, v1)

(u2, v2)

(u3, v3)

x1,y1,z1

x2,y2,z2

x3,y3,z3

GamesGames

avatar

Userinput

rendering interaction

AnimateIt(dt), DrawIt() ControlIt(dt),InteractIt()

Game objectsGame objects ControlIt:

– Interacts, thinks and applies his available controls (e.g. runs, shoots)

InteractIt – Looks at the states of other objects, checks collisions

AnimateIt: – Moves to its new position according to the elapsed time

DrawIt: – Draws itself onto the screen

Simulation loopSimulation loop ( (Game loopGame loop))

void IdleFunc( ) { // idle call back float old_time = time; time = glutGet( GLUT_ELAPSED_TIME ); float dt = time - old_time;

avatar -> ProcessInput( ); world -> Control( dt ); world -> Animate( dt );

glClearColor(0, 0, 0, 0); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); avatar -> SetCameraTransform(); world -> Draw( ); glutSwapBuffers( );}

dt

Data structure of the virtual worldData structure of the virtual world

Game Objects are dynamic (killing) Game objects are different (heterogeneous collection) Parent-child relationships (owner-weapon)

terrain skyavatar

Enemy1

Enemy2

world

bulletexplosion

Join: új elem hozzávételeWeapon

TerrainTerrain

Complex geometry– Height field

Complex texture No Control No Animation Collision detection, Lifts objects

Terrain geometryTerrain geometry

z

x,yx

yz

z = height(x,y) Height function definition:Discrete samples + linear interpolation

Discrete samples = B&W ImageDiscrete samples = B&W Image

Height map Triangle mesh

Reducing the number of Reducing the number of triangles: Level of detailtriangles: Level of detail

Height-field texturing: Height-field texturing: projecting the top viewprojecting the top view

y

x

u

v

Terrain improvement: Terrain improvement: Detail mapDetail map

Terrain collision Terrain collision detectiondetection

if (height(x,y) > z)

Collision!

Walking on the terrain:

Position(x, y) = (x, y, height(x,y) + legsize)

z

x,y

Bi-linear Height field interpolationBi-linear Height field interpolationfloat Height( float x, float y ) { x += wwidth/2; y += wlength/2; x = x / wwidth * w; y = y / wlength * l; int X = (int)x, Y = (int)y; float h1 = height_field[Y * w + X] * wheight; float h2 = height_field[Y * w + X+1] * wheight; float h3 = height_field[(Y+1) * w + X] * wheight; float h4 = height_field[(Y+1) * w + X+1] * wheight; float xd = x - X; float yd = y - Y; float hx1 = h1 + xd * (h2 - h1); float hx2 = h3 + xd * (h4 - h3); return (hx1 + yd * (hx2 - hx1)); }

SkySky

Image that is textured onsomething: sphere

Sky geometry: dome, sphere No Control No Animation No collision detection

Definition of surfaces as Definition of surfaces as triangle meshes: Tessellationtriangle meshes: Tessellation1. Find a parametric equation of a sphere:

x(u,v) = x0 + r cos 2u sin v y(u,v) = y0 + r sin 2u sin vz(u,v) = z0 + r cos v u,v [0,1]

2. Select points in the unit rectangle

GLU Quadrics: SphereGLU Quadrics: SphereGLUquadricObj * quadric; // definitionquadric = gluNewQuadric( );gluQuadricTexture(quadric, GL_TRUE);

// drawglBindTexture(GL_TEXTURE_2D, sky_texture_id);gluSphere(quadric, sky_radius, 32, 20);

EnemyEnemy

Animated geometry– Defined by keyframes

organized as clips Stand, run, attack, die,

– + mesh animation Textures (animated) Artificial intelligence Collision detection

Keyframe animation: runningKeyframe animation: running

Inbetweening: Computation of Inbetweening: Computation of frames from keyframesframes from keyframes

keyframest

Nonlinear interpolation

linear interpolation

What and how to interpolateWhat and how to interpolate High quality animation:

– Newton’s laws: the second derivative of a motion curve is proportional to the force, which acts through an elastic mechanism: interpolation curve is C2

– Even the interpolated frames should meet physical constraints: Bone animation

Games:– Linear interpolation– Interpolate the vertices of the mesh:

Mesh deformation

Example for bone animationExample for bone animation

Cyclic walkCyclic walk

Mesh Mesh morphingmorphing::t= 0

t= 1

Two neighboring keyframes

Time: t

Current vertex positions

Linear interpolation for

each vertex

Running as mesh morphingRunning as mesh morphing

+ position animation:

position += velocity * dt

Motion definitionMotion definition

Keyframes are organized into clips Keyframes are designed off line and stored

in a file: MD2, MD3, etc. file formats Typical clips in a game:

– Run, stand, attack, die, pain, salute, crouch, wave, point, taunt, etc.

ClipsClips

Stand40 keyframes

Run5 keyframes

Salute11 keyframes

Motion controlMotion control

AI stateAI machine

Keyframeanimation

Clip = start, stop keyframe

Keyframesstored in an

MD2 file

time: t

Vertex positions of a triangle mesh

Artificial Intelligence of an EnemyArtificial Intelligence of an Enemy

Dont Care Escape

Chase Attack

Dying

Dist < 4 &&Avatar_angle > 60

Dist < 4 &&Avatar_angle < 40

Collisionwith the bullet

Dist < 1

Dist > 1

Dist > 6Avatar_angle < 20

Avatar_angle

Avatar

TextTexturinguring

BulletBullet

Geometry: sphere Textured Not intelligent Physical animation

Physical animation Physical animation of the bulletof the bullet

t

t+dt

acceleration = (0, 0, -g)velocity += acceleration * dtposition += velocity * dt

force, acceleration

velocity

The bullet is flyingThe bullet is flying: : AAnimate, nimate, DDrawrawvoid Bullet::AnimateIt( float dt ) { acceleration = Vector(0,0,-g); speed += acceleration * dt; position += speed * dt;}

void Bullet::DrawIt( ) { glPushMatrix( ); glTranslate(position.x, position.y, position.z); glBindTexture(GL_TEXTURE_2D, bullet_texture); gluSphere(quadric, 1.0, 16, 10); glPopMatrix( );}

Collision detection between Collision detection between two slow objectstwo slow objects

dist = obj1.position - obj2.positionmin = obj1.BoundingRadius() + obj2.BoundingRadius()if (dist.Length() < min) Collision!

given t

Problem with fast objects

t

t + t

Bullet collision detectionBullet collision detectionBullet::InteractIt( GameObject * obj ) { if (obj->GetType() == TERRAIN) { Mountain * terrain = (Mountain *)obj; if (terrain->Height(position.x, position.y)> position.z) { KillIt(); world -> Join(new Explosion(position)); } } if ( obj->GetType() == AVATAR || obj->GetType() == ENEMY ) { if (“bounding spheres overlap”) { KillIt(); obj -> KillIt( ); world -> Join(new Explosion(position)); } }}

Collision detection with fast objectsCollision detection with fast objects: :

ray-tracingray-tracing

velocity

rel_velocity = velocity - vel2ray: position + rel_velocity·t

If (ray intersects bounding sphere first AND tintersect < dt) Collision!

hit_object = world->Intersect(position,velocity,t);

ship1 ship2 avatar space sun

world

bulletexplosion

position

vel2

BillboardsBillboards Single semi-transparent texture on an

oriented quadrilateral

pos

pos

QUAD

QUAD

Tmodell Tview Tperspectivexyz

XYZ

positionorientation

camera positioncamera orientation

ExplosionExplosion Seemingly complex, random

structure Similar look from all directions Collection of billboards

Particle system

Particle SystemsParticle Systems

position: position += velocity * dtvelocity: velocity += acceleration * dtacceleration: acceleration = force / weight

lifetimeage: age += dt; if (age > lifetime) Kill();

size, dsize: size += dsize * dt;weight, dweight: weight += dweight * dtcolor, dcolor: color += dcolor * dt

global force field(smoke)

randominitialvalues

Explosion settingsExplosion settings

position = Rand( center, 0.1 );lifetime = Rand( 2.0, 1.0 );

size = 0.001; dsize = Rand( 1.0, 0.5 ) / lifetime / 2.0;

velocity = Rand( CVector(0, 0, 0), 0.4 );acceleration = Rand( CVector(0, 0, 0), 0.4 );

color = Rand( Color(1, 0.5, 0, 1), Color(0, 0.5, 0, 0) );dcolor = Color(0, -0.5, 0, -1) / lifetime / 2;

Rand

AvatarAvatar

Keyboard controls its behavior:– ProcessInput

Its position and orientation will be the camera position and orientation before rendering– SetCameraTransform

Avatar :: SetCameraTransformAvatar :: SetCameraTransformAvatar :: SetCameraTransform( ) { glMatrixMode(GL_MODELVIEW); glLoadIdentity(); gluLookAt(position.x, position.y, position.z,

position.x + head.x, position.y + head.y, position.z + head.z,

up.x, up.y, up.z);}

eye

lookat

up = [0, 1, 0]

Keyboard controlKeyboard control

KeyboardFuncSpecialFunc

input

IdleFunc:GameLoop

virtualworld

IsSpace, IsLeft, IsRight, IsUp, IsDown

Game engineGame engine

GameObjectposition, velocity, accelerationControlIt(float dt )AnimateIt(float dt)InteractIt( GameObject * o) DrawIt( )IntersectIt(Ray r, float& t)

MemberControl, Animate, DrawInteract, Intersect, Join

TexturedObject

next

AvatarProcessInput()

SetCameraTransform()

TextureLoad( char * fname)

BillBoardDrawIt()

ParticleSystemEmit(int n)

Particle

GLUTWindow

GameEngineDisplayFunc

IdleFuncKeyPress

world

avatar

500 C++ lines

Shooting gameShooting game

TexturedObjectAvatar ParticleSystem

SkyDrawIt

TerrainDrawIt

AnimateIt

SelfProcessInput

ControlItInteractIt

ExplosionControlIt

EnemyDrawIt

InteractItControlIt

GameEngine

SpaceGame

350 C++ lines

Indoor games?Indoor games?

No terrain Building

– Cannot be represented by a height field– Textured triangle mesh

Collision: without checking all triangles Fast visibility: quickly eliminating the potentially

invisible objects

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