Implementation of an Outdoor Shooting Game

1. Implementation of an Outdoor Shooting Game Szirmay-Kalos László Budapest University of Technology email: szirmay@iit.bme.hu Web: http://www.iit.bme.hu/~szirmay

2. Demo 1: The objective

3. Virtual reality Virtual world avatar rendering interaction User input

4. Tasks 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)

5. I/O libraries simulation Windows + GLUT input Virtual world rendering OpenGL

6. I/O management initialization callback registration Operating System Windows main GLUT DisplayFunc KeyboadFunc SpecialFunc callbacks IdleFunc OpenGL Graphics hardware application

7. Rendering with OpenGL Perspective transformation Virtual world Viewing transformation 2. 1.  628 1325 1325 628 clipping visibility: z-buffer display

8. Geometry definition glBegin(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(); x12,y12,z12 x13,y13,z13 x11,y11,z11 glColor4f(R,G,B,A)

9. Texturing

10. Texture mapping (u2, v2) x3,y3,z3 (u1, v1) (u3, v3) x2,y2,z2 x1,y1,z1 glEnable(GL_TEXTURE_2D); glBindTexture(GL_TEXTURE_2D, texture_id); // which texture glBegin(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);

11. ControlIt(dt), InteractIt() AnimateIt(dt), DrawIt() Games avatar rendering interaction User input

12. Game objects • ControlIt: • Interacts, thinks and applies his available controls (e.g. runs, shoots) • InteractIt • Looks at the states of other objects, checkscollisions • AnimateIt: • Moves to its new position according to the elapsed time • DrawIt: • Draws itself onto the screen

13. Simulation loop (Game loop) dt 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( ); }

14. Data structure of the virtual world • Game Objects are dynamic (killing) • Game objects are different (heterogeneous collection) • Parent-child relationships (owner-weapon) world avatar Enemy 2 bullet explosion terrain sky Enemy 1 Weapon Join: új elem hozzávétele

15. Terrain • Complex geometry • Height field • Complex texture • No Control • No Animation • Collision detection, • Lifts objects

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

17. Discrete samples = B&W Image Height map Triangle mesh

18. Reducing the number of triangles: Level of detail

19. Height-field texturing: projecting the top view y x v u

20. Terrain improvement: Detail map

21. Terrain collision detection if (height(x,y) > z) Collision! Walking on the terrain: Position(x, y) = (x, y, height(x,y) + legsize) z x,y

22. Bi-linear Height field interpolation float 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)); }

23. Sky • Image that is textured on something: sphere • Sky geometry: dome, sphere • No Control • No Animation • No collision detection

24. Definition of surfaces as triangle meshes: Tessellation 1. Find a parametric equation of a sphere: x(u,v) = x0 + r cos 2u sin v y(u,v) = y0 + r sin 2u sin v z(u,v) = z0 + r cos vu,v[0,1] 2. Select points in the unit rectangle

25. GLU Quadrics: Sphere GLUquadricObj * quadric; // definition quadric = gluNewQuadric( ); gluQuadricTexture(quadric, GL_TRUE); // draw glBindTexture(GL_TEXTURE_2D, sky_texture_id); gluSphere(quadric, sky_radius, 32, 20);

26. Enemy • Animated geometry • Defined by keyframes organized as clips • Stand, run, attack, die, • + mesh animation • Textures (animated) • Artificial intelligence • Collision detection

27. Keyframe animation: running

28. Inbetweening: Computation of frames from keyframes Nonlinear interpolation linear interpolation keyframes t

29. What 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

30. Example for bone animation

31. Cyclic walk

32. Mesh morphing: t= 0 Time: t Two neighboring keyframes Linear interpolation for each vertex t= 1 Current vertex positions

33. Running as mesh morphing + position animation: position += velocity * dt

34. Motion 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.

35. Clips Stand 40 keyframes Run 5 keyframes Salute 11 keyframes

36. Motion control AI machine AI state time: t Keyframes stored in an MD2 file Clip = start, stop keyframe Keyframe animation Vertex positions of a triangle mesh

37. Artificial Intelligence of an Enemy Dist < 4 && Avatar_angle < 40 Dont Care Escape Dist > 6 Avatar_angle < 20 Dist < 4 && Avatar_angle > 60 Dist < 1 Chase Attack Dist > 1 Collision with the bullet Dying Avatar_angle Avatar

38. Texturing

39. Bullet • Geometry: sphere • Textured • Not intelligent • Physical animation

40. Physical animation of the bullet t+dt velocity t force, acceleration acceleration = (0,0,-g) velocity += acceleration * dt position += velocity * dt

41. The bullet is flying: Animate, Draw void 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( ); }

42. Collision detection between two slow objects Problem with fast objects t given t t +  t dist = obj1.position - obj2.position min = obj1.BoundingRadius() + obj2.BoundingRadius() if (dist.Length() < min) Collision!

43. Bullet collision detection Bullet::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)); } } }

44. Collision detection with fast objects: ray-tracing position rel_velocity= velocity - vel2 ray: position + rel_velocity·t If (ray intersects bounding sphere first AND tintersect < dt) Collision! vel2 velocity hit_object = world->Intersect(position,velocity,t); world avatar ship1 ship2 space sun bullet explosion

45. Billboards • Single semi-transparent texture on an oriented quadrilateral pos pos QUAD X Y Z x y z Tmodell Tview Tperspective QUAD position orientation camera position camera orientation

46. Explosion • Seemingly complex, random structure • Similar look from all directions • Collection of billboards • Particle system

47. Particle Systems global force field (smoke) position: position += velocity * dt velocity: velocity += acceleration * dt acceleration: acceleration = force / weight lifetime age: age += dt; if (age > lifetime) Kill(); size, dsize: size += dsize * dt; weight, dweight: weight += dweight * dt color, dcolor: color += dcolor * dt random initial values

48. Explosion settings Rand 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;

49. Avatar • Keyboard controls its behavior: • ProcessInput • Its position and orientation will be the camera position and orientation before rendering • SetCameraTransform

50. Avatar :: SetCameraTransform Avatar :: 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 up = [0, 1, 0] lookat