Ray Tracing Basics. Announcements. CS4620/5620: Lecture 8. Shading. Image so far. Lambertian shading. Diffuse reflection. PA1 out.

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1 CS4620/5620: Lectue 8 Ray Tacig Basics Aoucemets PA1 out I pais: PA0 (fid pates), stay afte cass to fid pates, o post o piazza, o cotact the TAs,... capped cyide, coe Staff ist cs4620-staff-@coe.edu Coe CS4620/562- Fa 2011!Lectue Shadig With eye ay geeatio ad scee itesectio fo 0 <= iy < y fo 0 <= ix < x { ay = camea.getray(ix, iy); c = scee.tace(ay, 0, +if); image.set(ix, iy, c); Scee.tace(ay, tmi, tmax) { suface, t = sufs.itesect(ay, tmi, tmax); if (suface!= u) etu suface.coo(); ese etu back; Compute ight efected towad camea Iputs: eye diectio ight diectio (fo each of may ights) suface oma suface paametes (coo, shiiess, ) 3 4 Diffuse efectio Lambetia shadig Light is scatteed uifomy i a diectios the suface coo is the same fo a iewig diectios Lambet s cosie aw Shadig idepedet of iew diectio iumiatio fom souce L d = k d I max(0, ) diffuse coefficiet Top face of cube eceies a cetai amout of ight Top face of 60º otated cube itecepts haf the ight I geea, ight pe uit aea is popotioa to cos! = diffusey efected ight 5 6

2 Lambetia shadig Diffuse shadig Poduces matte appeaace [Foey et a.] k d 7 8 Scee.tace(Ray ay, tmi, tmax) { suface, t = hit(ay, tmi, tmax); if suface is ot u { poit = ay.eauate(t); oma = suface.getnoma(poit); etu suface.shade(ay, poit, oma, ight); ese etu backgoudcoo; Suface.shade(ay, poit, oma, ight) { = omaize(ay.diectio); = omaize(ight.pos poit); // compute shadig Light Loca ight Positio Diectioa ight (e.g., su) Diectio, o positio 9 10 Shadows Suface is oy iumiated if othig bocks its iew of the ight With ay tacig it s easy to check just itesect a ay with the scee! Suface.shade(ay, poit, oma, ight) { shadray = (poit, ight.pos poit); if (shadray ot bocked) { = omaize(ay.diectio); = omaize(ight.pos poit); // compute shadig etu back; 11 12

3 Shadow oudig eos Souds ike it shoud wok, but hmm... Shadow oudig eos Souds ike it shoud wok, but hmm... What s goig o? What s goig o? hit: at what t does the shadow ay itesect the suface you e shadig? Shadow oudig eos Mutipe ights Soutio: shadow ays stat a tiy distace fom the suface Just oop oe ights, add cotibutios Impotat to fi i back shadows Ambiet shadig back shadows ae ot eay ight oe soutio: dim ight at camea ateatie: add a costat ambiet coo to the shadig Do this by moig the stat poit, o by imitig the t age shade(ay, poit, oma, ights) { esut = ambiet; fo ight i ights { if (shadow ay ot bocked) { esut += shadig cotibutio; etu esut; Specua shadig (Phog) Itesity depeds o iew diectio bight ea mio cofiguatio measue ea by dot poduct of uit ectos 17 18

4 Specua shadig (Phog) Itesity depeds o iew diectio bight ea mio cofiguatio Refected diectio Itesity depeds o iew diectio efects icidet ight fom mio diectio Specua shadig (Bi-Phog) Phog mode pots Cose to mio haf ecto ea oma Iceasig aows the obe h h = bisecto(, ) = + + L s = k s I max(0, cos α) p = k s I max(0, h) p [Foey et a.] specuay efected ight specua coefficiet Specua shadig Diffuse + Phog shadig k s [Foey et a.] p 23 24

5 Ambiet shadig Shadig that does ot deped o aythig add costat coo to accout fo disegaded iumiatio ad fi i back shadows Puttig it togethe Usuay icude ambiet, diffuse, Phog i oe mode L = L a + L d + L s = k a I a + k d I max(0, ) + k s I max(0, h) p The fia esut is the sum oe may ights L a = k a I a efected ambiet ight ambiet coefficiet 25 N L = L a + [(L d ) i + (L s ) i ] L = k a I a + i=1 N [k d I i max(0, i ) + k s I i max(0, h i ) p ] i=1 26 Mio efectio Mio efectio Coside pefecty shiy suface (a mio) thee is t a highight istead thee s a efectio of othe objects Ca ede this usig ecusie ay tacig to fid out mio efectio coo, ask what coo is see fom suface poit i efectio diectio aeady computig efectio diectio fo Phog Gazed mateia has mio efectio ad diffuse Itesity depeds o iew diectio efects icidet ight fom mio diectio = + 2(( ) ) = 2( ) whee L m is eauated by tacig a ew ay Diffuse + mio efectio (gazed) (gazed mateia o foo) Ray tace achitectue 101 You wat a cass caed Ray poit ad diectio; eauate(t) possibe: tmi, tmax Some thigs ca be itesected with ays idiidua sufaces, goups of sufaces (acceeatio goes hee), the whoe scee make these a subcasses of Suface imit the age of aid t aues (e.g. shadow ays) Oce you hae the isibe itesectio, compute the coo may wat to sepaate shadig code fom geomety sepaate cass: Mateia (each Suface hods a efeece to oe) its job is to compute the coo 29 30

6 Achitectua pacticaities Retu aues suface itesectio teds to wat to etu mutipe aues t, suface o shade, oma ecto, maybe suface poit i may pogammig aguages (e.g. Jaa) this is a pai typica soutio: a itesectio ecod a cass with fieds fo a these thigs keep tack of the itesectio ecod fo the cosest itesectio Achitectua pacticaities Efficiecy i Jaa the (o, a) key to beig fast is to miimize ceatio of objects what objects ae ceated fo eey ay? ty to fid a pace fo them whee you ca euse them. Shadow ays ca be cheape (ay itesectio wi do, do t eed cosest) but: Fist Get it Right, The Make it Fast 31 32

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