Ob­serve how light in­ter­acts with mat­ter, and cre­ate ad­vanced shad­ing ef­fects in Hou­dini and Clarisse

3D Artist - - THE PIPELINE -

Greg Barta

scivfx Light&ma­te­rial One, 2018


Hou­dini, Clarisse

Learn how to

• Ob­serve light and

mat­ter in­ter­ac­tion

• Add ex­tra de­tails to

the shad­ing

• Use dy­nam­ics and other tricks to achieve richer shad­ing ef­fects

• Do ex­per­i­ments with real-world ob­jects to un­der­stand how things work


This study scene was cre­ated for Isotropix to use as a demon­stra­tion of Clarisse. It is based on scanned ob­jects, while the back­ground is my pho­togram­me­try and the stat­ues are from

It is a trend in VFX and other Cg fields that artists use ‘uber’ shaders that deal with al­most all of the usual ma­te­rial ef­fects we see in daily life. how­ever, there are some kind of phe­nom­ena that can’t be ren­dered with these shaders. ad­di­tion­ally, work­ing with these is more like be­ing a dj – you mix to­gether the dif­fer­ent shad­ing be­hav­iours, which were orig­i­nally cre­ated by shader writ­ers. as the best djs are also mu­si­cians, we can get bet­ter re­sults if we learn more about how light in­ter­acts with mat­ter and also re-cre­ate these shad­ing ef­fects from scratch, even in­vent­ing new ways to add an ex­tra layer of re­al­ism or a unique look to avoid re­sults that are too stan­dard­ised.

Ob­serve di­rectly We can achieve the most de­tailed and ad­e­quate shad­ing ef­fects if we do re­search, which in­cludes di­rect and in­di­rect ob­ser­va­tions. di­rectly, we can ob­serve dif­fer­ent op­ti­cal phe­nom­ena – one of the best times is dur­ing cook­ing and food prepa­ra­tion as a very wide range of ma­te­rial ef­fects is there si­mul­ta­ne­ously. Just ob­serve how flour or grounded seed gets darker but more spec­u­lar with wa­ter, or how the egg white con­verts from a di­elec­tric-like ma­te­rial to sub­sur­face scat­ter­ing one. an­other ad­van­tage is that you can touch and smell these ma­te­ri­als, which is in con­trast with the in­tan­gi­ble na­ture of Cg. The shape of light We can use any dis­play – a mon­i­tor or smart­phone – as an ar­bi­trary shaped and tex­tured light source to study how the shape of it can af­fect the char­ac­ter of the light­ing, es­pe­cially the penum­bra area of the shad­ows. this is sim­i­lar to the light­ing in Grav­ity and many other mod­ern movies, just on a smaller scale. We can com­pare sim­ple shapes like square and cir­cle. You can imag­ine your­self as an ant walk­ing through this blurry edge. the area of a square shape de­cays lin­early from your view­point but the area de­cay of a cir­cle – thus the in­com­ing light amount – is si­nu­soidal in the func­tion of the dis­tance.

Real-time shaders in Clarisse we get the fi­nal shad­ing in the 3d view­port be­cause it is also ray­traced. how­ever, the view­port in re­cent hou­dini ver­sions can show the shad­ing and light­ing ef­fects with dis­place­ments very well, es­pe­cially if we use the Prin­ci­pled shader. For vir­tual cin­e­matog­ra­phy work, it’s im­por­tant to see our scene with a de­cent level of light­ing and shad­ing but with smooth play­back and in­ter­ac­tion. in other cases it’s rec­om­mended to switch back to con­stant shad­ing with wire­frame in the view­port. this makes the scene more ab­stract and your eyes won’t adapt to the game-like visuals, which is an ad­van­tage for the ren­der­ing de­ci­sions later.

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