Illumination Models. To calculate the color of an illuminated position on the

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1 llumination Models 5 th Week, 2008 Sun-Jeong Kim Realistic Scene in CG Perspective projection of objects + natural lighting effects to the visible surface Light reflections, transparency, surface texture, and shadows llumination model (lighting model) To calculate the color of an illuminated position on the surface of an object Surface-rendering method Using the color calculations l from an illumination i model to determine the pixel colors for all projected positions in a scene 2

2 Light Sources Any object that is emitting radiant energy Simple light-source models: Point light sources Directional light sources Spotlight sources Luxo (courtesy by Pixar) 3 Point Light Sources The simplest light model Position of the light source ntensity (== the color of the emitted light) Coefficients for attenuation effects (x, y, z) (r, g, b) (x l, y l, z l ) (r l, g l, b l ) (a 0, a 1, a 2 ) d l =sqrt((x x l ) 2 +(y y l ) 2 +(z z l ) 2 ) f atten (d l )= 1 / (a 0 +a 1 d l +a 2 d l2 ) r = r l f atten (d l ) g = g l f atten (d l ) b = b l f atten (d l ) 4

3 Directional Light Sources nfinitely distant light sources Direction of the light source ntensity No attenuation effects! (x, y, z) (r, g, b) (x l, y l, z l ) (r l, g l, b l ) r = r l g = g l b = b l 5 Spotlight Sources Directional light sources and spotlight effects Position of the light source ntensity Angular intensity attenuation Attenuation exponent : f atten (α)= cos a lα Direction and an angle : V obj V light = cosα cos θ l 6 r = r l f atten (α) g = g l f atten (α) b = b l f atten (α)

4 OpenGL Lighting Must enable lighting calculation and each light source glenable(gl_lghtng); LGHTNG); glenable(gl_lghti); i=0, 1,, 7 Assigning all colors based on light sources and material properties not by glcolor*() Must supply the normal vectors glnormal*() Some functions such as glutsolidteapot() will compute normals glnormal3{bsidf}(type dx, TYPE dy, TYPE dz); glnormal3{bsidf}v(type *value); 7 Specifying a Light Source Creating a light source gllight{if}(glenum light, GLenum param, TYPE value); gllight{if}v(glenum light, GLenum param, TYPE *value); light GL_LGHT0, LGHT0 GL_LGHT1, LGHT1, GL_LGHT7LGHT7 param GL_POSTON, GL_DFFUSE, GL_SPECLAR, GL_AMBENT, GL_SPOT_DRECTON, GL_CONSTANT_ATTENUATON, ATTENUATON, GL_LGHT0 : a default light source Diffuse and specular white(1 1.0, 1.0, 1.0, 1.0) Position ( 0.0, 0.0, 1.0, 0.0 ) 8

5 Directional light Light Sources GL_POSTON, GL_DFFUSE, GL_SPECULAR, GL_AMBENT Point light GL_CONSTANT_ATTENUATON ATTENUATON (default: 1), GL_LNEAR_ATTENUATON (default: 0), GL _QUADRATC_ ATTENUATON (default: 0) Spotlight GL_SPOT_DRECTON, GL_SPOT_CUTOFF, GL_SPOT_EXPONENT 9 Phong Reflection Model A basic illumination model Ambient light Diffuse reflection Specular reflection L N R θ θ V 10

6 Background lighting Ambient Light Setting by a general brightness level for a scene Uniform ambient lighting The same for all objects To approximate the global l diffuse reflections from the various illuminated surfaces 11 Diffuse Reflection (1) The incident light is scattered with equal intensity in all directions ndependent of the viewing position Lambert s cosine law = k cosθθ diff diff d = kd l l ( N L) k d : diffuse-reflection coefficient or diffuse reflectivity 12

7 Diffuse Reflection (2) Ambient light + diffuse reflection k a : ambient-reflection coefficient k = = k ( N L ) amb a a diff = d l 13 Specular Reflection (1) The bright spot on a shiny surface Total, or near total, reflection of the incident light in a concentrated region around the specular-reflection reflection angle n = k cos s φ k s spec n s : specular-reflectionreflection exponent spec = k s s l l n ( V R) s 14

8 Plots of cos n s φ Specular Reflection (2) Different specular exponent n s 15 Specular Reflection (3) Specular reflection spec = k s l n ( V R) s 16

9 Blinn Specular-Reflection Model Specular reflection vector Halfway vector R + L = R = 2 2( N L) N ( N L ) N L variable vector H = L + V L + V ( θ α ) φ θ + α = + 2α = φ spec n = k ( V R) ( ) s n = k N H s s l spec s l 17 Combined Ambient, Diffuse and Specular Reflections (1) A single light source = + + = k amb diff Multiple l light sources a a + k d l spec n ( N L) + k ( V R) s n = amb + + ( l, dff diff + l, spec ) = k a a + l= 1 n l= 1 l s ns ( k ( N L ) + k ( V R ) ) d l s 18

10 Combined Ambient, Diffuse and Specular Reflections (2) Wireframe Ambient Lighting Only Ambient + Diffuse 19 Ambient + Diffuse + Specular Drawing GLUT Objects (1) 20

11 Drawing GLUT Objects (2) 21 Drawing GLUT Objects (3) 22

12 Drawing GLUT Objects (4) 23 Drawing GLUT Objects (5) 24

13 Result Drawing GLUT Objects 25 Exercises (1) 원뿔의높이를 y 축과일치하도록세우시오. 26

14 GLUT Solid Objects 27 Result GLUT Solid Objects 28

15 Exercises (2) 전역변수 angle 을이용하여, 각각의 object 의 local y축을중심으로회전시키시오. 29 Rotations 30

16 Exercises(3) 삼각형이회전하면서사라지는이유는무엇인가? 삼각형이사라지지않도록프로그램을수정하시오. 31 Enabling Lighting 32

17 What s Wrong? 33 Normal Vectors 34

18 Result Enabling Lighting 35 Disabling Lighting 36

19 Result Disabling Lighting 37 Directional Light Source 38

20 Result Directional Light Source 39 Ambient Light 40

21 Result Ambient Light 41 Diffuse Reflection 42

22 Result Defuse Reflection 43 Specular Reflection 44

23 Result Specular Reflection 45 Point Light Source (1) 46

24 Result Point Light Source (1) 47 Point Light Source (2) 48

25 Result Point Light Source (2) 49 Exercises (4) 다음아래와같이 Light Source 의 Position 을설정하는코드가 nitscene() 모듈안에놓이는경우와, DrawScene() 모듈에서 glulookat() 함수이후에놓이는경우의차이점을설명하시오. float light_pos0[4] = { 0.0f, 0.0f, -4.0f, 1.0f }; gllightfv( GL_LGHT0, GL_POSTON, light_pos0 ); 50

26 Rotation of Point Light (1) 51 Result Rotation of Point Light (1) 52

27 Rotation of Point Light (2) 53 Result Rotation of Point Light (2) 54

28 Attenuation of the Point Light (1) 55 Attenuation of the Point Light (2) 56

29 Result Attenuation of the Point Light 57 Exercises (5) 다음 Attenuation Parameter 들의값을변경해보시오. gllightf( GL_LGHT0, GL_CONSTANT_ATTENUATON, 0.0f ); gllightf( GL_LGHT0, GL_LNEAR_ATTENUATON, 0.0f ); gllightf( GL_LGHT0, GL_QUADRATC_ATTENUATON, _ 1.0f ); 각 Parameter aa ee의의미또는역할에대해설명해보시오. 58

30 Spotlight (1) 59 Result Spotlight (1) 60

31 Spotlight (2) 61 Result Spotlight (2) 62

32 Multiple Light Sources 63 Result Multiple Light Sources 64

33 Exercises (6) 3 종류의광원 (point light, directional light, and spotlight sources) 들을생성하시오. 3 개광원의속성 ( 위치와색상 ) 은반드시서로다르게설정할것 다음의키를누르면, 위에서생성한광원들중일부만활성되도록만드시오. p or P : point light source d or D : directional light source s or S : spotlight source a or A : all three light sources 65 Exercises (7) Point Directional Spot 66 All Together