Lighting. Dr. Scott Schaefer

Transcription

1 Lghtng Dr. Scott Schaefer 1

2 Lghtng/Illumnaton Color s a functon of how lght reflects from surfaces to the eye Global llumnaton accounts for lght from all sources as t s transmtted throughout the envronment Local llumnaton only accounts for lght that drectly hts a surface and s transmtted to the eye 2/49

3 Global Illumnaton Image taken from 3/49

4 Reflecton Models Defnton: Reflecton s the process by whch lght ncdent on a surface nteracts wth the surface such that t leaves on the ncdent sde wthout change n frequency. 4/49

5 Types of Reflecton Functons Ideal Specular Reflecton Law Mrror Ideal Dffuse Lambert s Law Matte Specular Glossy Drectonal dffuse 5/49

6 Illumnaton Model Ambent Lght Unform lght caused by secondary reflectons Dffuse Lght Lght scattered equally n all drectons Specular Lght Hghlghts on shny surfaces 6/49

7 Ambent Lght I k A =ntensty of ambent lght k a =ambent reflecton coeffcent a A Really 3 equatons! (Red, Green, Blue) Accounts for ndrect llumnaton Determnes color of shadows 7/49

8 Total Illumnaton I k a A 8/49

9 Dffuse Lght Assumes that lght s reflected equally n all drectons Handles both local and nfnte lght sources Infnte dstance: L doesn t change Fnte dstance: must calculate L for each pont on surface N L Surface 9/49

10 Dffuse Lght I Ck d cos( ) Ck ( LN) C = ntensty of pont lght source k d = dffuse reflecton coeffcent = angle between normal and drecton to lght d cos( ) LN L N Surface 10/49

11 Lambert s Law Beam of Lght N Surface I Lght Area Beam Wdth I Surface Area source 11/49

12 Lambert s Law Beam of Lght N Surface I Lght Area Beam Wdth I Surface Area source Beam Wdth Surface Area cos( ) 12/49

13 Lambert s Law Beam of Lght N Surface I Lght Area Beam Wdth I Surface Area source I source ( LN) Beam Wdth Surface Area cos( ) 13/49

14 Total Illumnaton I k a A 14/49

15 Total Illumnaton I k a Ak d C( LN) 15/49

16 Specular Lght Perfect, mrror-lke reflecton of lght from surface Forms hghlghts on shny objects (metal, plastc) L N R E Surface 16/49

17 Specular Lght n n I Cks cos ( ) Cks( RE) C = ntensty of pont lght source k s =specular reflecton coeffcent =angle between reflected vector (R) and eye (E) n =specular exponent cos() RE L N R E Surface 17/49

18 Fndng the Reflected Vector N L R Surface 18/49

19 Fndng the Reflected Vector L L N L R Surface 19/49

20 Fndng the Reflected Vector L Ncos( ) N( LN) L L L L L N L R Surface 20/49

21 Fndng the Reflected Vector R L L L L N L R Surface 21/49

22 Fndng the Reflected Vector R 2( LN) N L L N L L R Surface 22/49

23 Total Illumnaton I k a Ak d C( LN) 23/49

24 Total Illumnaton I k a AC k d ( LN) k ( R s E) n n5 24/49

25 Total Illumnaton I k a AC k d ( LN) k ( R s E) n n50 25/49

26 Total Illumnaton I k a AC k d ( LN) k ( R s E) n n500 26/49

27 Multple Lght Sources Only one ambent term no matter how many lghts Lght s addtve; add contrbuton of multple lghts (dffuse/specular components) 27/49

28 Total Illumnaton I k a AC k d ( LN) k ( R s E) n 28/49

29 Total Illumnaton I k a A C k d ( L N) k s ( R E) n 29/49

30 Attenuaton Decrease ntensty wth dstance from lght d = dstance to lght r = radus of attenuaton for lght att d, r) max(0,1 d ) ( r 2 att( d, r) max(0,1 d 2) att att 2 ( d, r) max 0, 1 d 2 r 2 d r 2 ( d, r) e r 2 30/49

31 Attenuaton I k a A C k d ( L N) k s ( R E) n att( d, r ) 31/49

32 Attenuaton I k a A C k d ( L N) k s ( R E) n att( d, r ) 32/49

33 Spot Lghts Elmnate lght contrbuton outsde of a cone A L Surface 33/49

34 Spot Lghts Elmnate lght contrbuton outsde of a cone spotcoeff L L Acos( ), Acos( ), 0 L A A L Surface 34/49

35 Spot Lghts I k a A C k d ( L N) k s ( R E) n spotcoeff 35/49

36 Spot Lghts I k a A C k d ( L N) k s ( R E) n spotcoeff 36/49

37 Spot Lghts I k a A C k d ( L N) k s ( R E) n spotcoeff 37/49

38 Implementaton Consderatons I k a AC k d ( LN) k ( R s E) n N Surface L 38/49

39 Implementaton Consderatons I k Two optons: 2-sded: negate a AC k N d for back-facng polygons 1-sded: f L N 0, I ka A // lght on back of surface else I k AC k ( L N) k max(0, R E) a ( LN) k ( R N d Surface s s E) n n L 39/49

40 40/49 Implementaton Consderatons Typcally choose Clamp each color component to [0,1] n s d a E R k N L k C A k I ) ( ) ( 1 s d a k k k

41 OpenGL and Lghtng Specfy normals for geometry Create/poston lghts Specfy materal propertes Select lghtng model 41/49

42 OpenGL and Lghtng Specfy normals for geometry Create/poston lghts Specfy materal propertes Select lghtng model 42/49

43 OpenGL and Lghtng glbegn(gl_triangles); glnormal3f(nx,ny,nz); glvertex3f(x,y,z); glend(); 43/49

44 OpenGL and Lghtng Specfy normals for geometry Create/poston lghts Specfy materal propertes Select lghtng model 44/49

45 OpenGL and Lghtng float lght_poston[] = {0, -10, 0, 1}; float lght_ambent[] = {.1,.1,.1, 1}; float lght_dffuse[] = {.9,.9,.9, 1}; float lght_specular[] = {1, 1, 1, 1}; gllghtfv(gl_light0, GL_POSITION, lght_poston); gllghtfv(gl_light0, GL_AMBIENT, lght_ambent); gllghtfv(gl_light0, GL_DIFFUSE, lght_dffuse); gllghtfv(gl_light0, GL_SPECULAR, lght_specular); glenable(gl_light0); glenable(gl_lighting); 45/49

46 OpenGL and Lghtng Specfy normals for geometry Create/poston lghts Specfy materal propertes Select lghtng model 46/49

47 OpenGL and Lghtng float mat_ambent[] = {1, 0, 0, 1}; float mat_dffuse[] = {1, 0, 0, 1}; float mat_specular[] = {1, 1, 1, 1}; float mat_shny[] = {50}; glmateralfv(gl_front, GL_AMBIENT, mat_ambent); glmateralfv(gl_front, GL_DIFFUSE, mat_dffuse); glmateralfv(gl_front, GL_SPECULAR, mat_specular); glmateralfv(gl_front, GL_SHININESS, mat_shny); 47/49

48 OpenGL and Lghtng Specfy normals for geometry Create/poston lghts Specfy materal propertes Select lghtng model 48/49

49 OpenGL and Lghtng gllghtmodelfv(gl_light_model_local_viewer, GL_TRUE); gllghtmodelfv(gl_light_model_two_side, GL_FALSE); 49/49