HDRI and Mental Ray

7/31/2019 HDRI and Mental Ray

1/16

BrendanFitzgerald

www.crazy8studio.com

[email protected]

HDRIandMentalRay+RenderPasses

DigitalMediaClub(www.dmcscad.com)April2,2008

Inmy

last

lecture,

Ishared

with

you

the

practical

application

of

photography

and

how

to

obtain

HDRIs

usingphotographictechniques. ThistimeIwillbetalkingabouttheimplementationofHDRIinaMaya

sceneandsometricksthatIhavelearned. Aswitheverythingelse,therearenumerouswaysofdoing

things,andwhatIplanonshowingyouisonewaythatworkedforme. ThePasseswewillcreateusing

onlyanHDRItolightoursceneare:

Diffuse

Specular

Shadow

Reflection

Ok,so

you

have

an

object

that

you

want

to

use

HDRI

with.

Lets

talk

about

how

to

go

about

doing

so.

Firstthingsfirst,letsopenoursceneandgetourobjectintoview.(YesthatsWootyouseeonmy

screen).

Figure1
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Ithinkthefirstandmostimportantthingtodoistomakesurethatthedefaultlightingisturnedoffin

therendersettings.YoudontwantthismuckingupyourHDRlitscene. Alsomakesurethatyoure

usingMentalRay.(Figure1.1)

Figure1.1Okmovingon.Whatsnext? OhIknow!SomeHDRIsweetness!Thatsright!LetsfindtheIBLsettings,

opentherendersettings(Figure1.2.1).YouseetheMentalRayTab?Innotchangeyourrendererto

Mentalray(Figure1.2.2). Clickthatandthenmovedowntotheenvironmentlineattheverybottom

andexpandthelinebyclickingonthearrow.SeethebuttonnexttoImageBasedLightingcalled

Create;clickthat(Figure1.2.2). Guesswhatwegetnow? Wegetashinynewenvironmentsphere

andawholetonofnewoptionsintheAttributeeditorfortheIBLNode. Letstalkaboutthenextmost

importantpart,whichisgettingyourimageontothesphere. JustclickonthefolderIconnexttothe

imagenameandloadupyourLightMap.OnceyourLightMapisloadedupitmayormaynotlook

weird.If

it

does

look

funny

its

most

likely

because

the

image

you

loaded

up

was

that

of

achrome

ball.

BydefaulttheMentalRayIBLnodeisnotsettohandlethisproperly.ItissettohandleaLat/Longfile

whichhasa2:1aspectratioandisbasicallyasphereunwrappedflat.Tofixthissimplychangethe

Mappingatthetoptoangular.(Figure1.2)


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Figure1.2.1

Figure1.2.2


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Figure1.2.3Oknowwehaveourlightmappluggedletstalkabouttherenderstatssection. Sinceweareonlygoing

tousetheIBLnodetoEmitlightandnothingelse,weneedtoturnoffsomestuffinhere.Firstweneed

to: turnoffPrimaryVisibilitysothatwedontseeourlightmap,turnoffVisibleasEnvironmentsothat

itsnotvisibleinPrimaryReflections,turnoffVisibleinSecondaryReflectionsandRefractions. Lets

leavevisibleinFinalGathereventhoughwewontbeusingitinthistutorial. Mightbefunforyouto

experimentwith!

(Figure

1.3)


5/16

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Figure1.3

Ifyouhavepressedrenderatalluptothispointandgotonlyblackdontworry,thatsok. Since

presentlywearentusingfinalgather,wearentusingreflectionsfromourlightmap. Sincewedisabled

defaultlightingwehaveeliminatedanyilluminationoradditiveprocessinthescene. So,letsaddsome

back! GototheIBLnodeattributeswhichshouldstillbeopeninyourattributeeditorandexpandthe

LightEmissionPart. NowIpersonallyamnotclearonwhatallthesettingsinherebecausequitefrankly

thereisnt

alot

of

documentation

on

the

subject

and

what

documentation

there

is,

is

lacking.

Ican

guide

youthroughtheimportantstuffthough.(Figure1.4)


6/16

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Figure1.4

First,clickthecheckboxthatsaysemitlightandjustlikethatwehaveturnedonthecomplexprocessof

emittinglightfromanimage. Itsalldownhillfromherenowait,uphillImean.Findingthosemagic

numberscanbefrustrating. ThefirstthingyouaregoingtodoissetyourQualityU/Vtothesizeofyour

LightMap. ThisjustsetsupAcontrolTextureforlightemission.EveryPixelinthattexturevirtually

representsadirectionallight.MayaHelpDocs. Thesenumberscangreatlyincreaseorreduceyour

rendertimessotreatthemwithcare.NextwehavetheSamples,andIthinkthebestexplanationcomes

fromthehelpdocsagain;Samplingalldirectionallightsrepresentedbythecontroltextureisoften

prohibitivelyexpensive.

Therefore

the

shader

has

abuilt

in

importance

mechanism

that

attempts

to

selecttheprimary(key)lights.MayaHelpDocs. BasicallywhatIhavefoundisthatincreasingthese

numbersincreasesyourrendertimebutalsoincreasesthequalityofyourshadowsandlight. Varyfocus

willoffsetthedirectionofallyourdirectionallightsrandomlyandimprovequality.Lastbutnotleast,

disablebacklightingwhichshouldonlybeuncheckedifyouhavesomethinginyourscenethatis

transparentlikeglassthatgreatlyoptimizesthesamplinginyourscene.

Whew,Ithinkthatcoversmostoftheimportantstuff! Ithinkeverythingelseisprettyselfexplanatory,

butthebestwaytolearnistojuststartclickingsomestuffandgetyourhandsdirty! Seewhatcomesof

it!(Figure1.4)


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Ok,letsgetthelastthingsetupsothatwecangetintotherenderpassespart.Ifyouhavenoticedby

nowwehaveeverythinginourbeautypassexceptforreflections. Addingreflectionsrequiresyouto

createapolygonsphere. Aftercreatingthepolygonsphereyouwillscaleittoaboutthesamesizeas

theIBLNode,andapplyasurfaceshadertothesphere.Afterapplyingthesurfaceshadertothesphere

youneedtogototheoutcolorofthesurfaceshaderandclickthecreaterendernodebuttonthatlooks

likeacheckerboxnexttotheattribute.(Figure1.5)

Figure1.5Atthispointitsimportantthatyourreflectionmapisalat/long.Ifitisnt,youcaneasilyfixthiswith

HDRshopbyjustlookinguppanoramictransformations.ThisisbecausetheIBListheonlyplacethatI

havefoundthatsupportsAngularmappinginMentalRay. Anyway,onceyougetthecreaterender

nodedialogboxmakesureyouchooseasprojectionandthenclickfile.Afterthatintheattribute

editorforyourshader,changetheProjectiontypetoSpherical.Nextselectyourlat/longandnowwhen

yourenderyouwillhavereflections.Youmightnoticethatyouseeyourreflectionmapinthe

background;this

is

an

easy

fix.

Select

the

polygon

sphere

and

pull

up

the

attribute

editor

and

go

to

renderstats.Turnoff:Primaryvisibility,CastShadows,ReceivesShadows,DoubleSidedandclick

opposite.NowyouhaveaspherethatonlycontributestoReflectionandRefraction,nothingelse.


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Figure1.6Dang.

Thats

alot

just

to

get

the

HDRI

lighting

setup,

so

now

we

should

break

it

down.

My

approach

to

thisproblemwas,Ithink,relativelysimple. IfyouthinkofusingEmitlightintheIBLnodeasthesame

thingasmakingatonofspotlightstheneverythingwillmakesense.(Figure1.6)

DiffusePass

Forthediffusepass,allwehavetodoiseliminateeverythingexceptforthediffuserays.Todothiswe

havetocreateanewrenderlayer.Makesurethatyoucreateanemptylayer(dontusetheaddselected

geometrytorenderlayerthisbuttoncanbebuggy). Afterwhichyoucanselecteverythingthathas

diffuseinitandrightclickandaddtothatlayer.Makesurethatyoudontaddthereflectionsphere,not

thatitreallymatters,butitwillhelpinkeepingyoursceneclean. Next,rightclickonyourrenderlayer

andgo

to

the

attributes

of

that

layer.

Turn

the

Override

on

for:

Cast

Shadows,

Receives

Shadows,

Visible

inRefractionsandReflections.NextgototheattributesfortheIBLnodeandunderEmitLightUncheck:

EmitSpecularandRaytraced.Youshouldhavesomethinglikebelow.(Figure1.7)


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Figure1.7Afterthatyoushouldgetarenderthatlookssomethinglikethiswithonlydiffuseinformationinthe

image. Asyoucanseewehaveseparatedoutthediffuseinformation.(Figure1.8)

Figure1.8


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Specular

Thisisprettymuchthesamestuffasbefore,socreatearenderlayerandcallitSpecular. Onceagain

addeverythingtothislayerthathasSpecularinformation.Alsowewanttosetupthislayerthesameas

thediffusepass.Afterthatssetup,gobackintotheattributeeditoroftheIBLnodeanduncheckEmit

DiffuseandCheckEmitSpecular.(Figure1.9)

Figure1.9NowPressrenderandyoushouldgetsomethinglikebelow.(Figure2)

Figure2Shadow

Nowtothefunpart,separatingouttheshadows.Onceagaincreateanewrenderlayerandadd

everythingtothescenethatreceivesshadows.OntheAttributesforthislayermakesurethatyouleave


11/16

BrendanFitzgerald


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castandreceiveshadowaloneon,turnoffreflections(thisalsomightnotmatter,butbettersafethen

sorry).OnceyouvedonethatgobacktotheEmitLightoptionsintheIBLnodeandturnmakesurethat

Emitdiffuse.NextgototheHypershadeandcreateaUseBackgroundShader.Intheusebackground

shadersetSpecularcolortoblack,Reflectivityto0,andReflectionlimitto0.Leaveshadowmaskwhite.

Lastly,whileyouhavetheshadowlayerselected,rightclickontheUseBackgroundShaderyoujust

createdandselectAsignMaterialOverride.Noweveryobjectinthislayerwillhavethisshaderapplied

inthislayer.(Figure2.1)

Figure2.1


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Afterallofthathitrenderonandyoushouldgetanimagethatlookssomethinglikethisinyouralpha

channel.(Figure2.2)

Figure2.2Almost

done

just

alittle

more.

This

next

one

should

be

interesting!

Reflections

SoinitiallyImustsaythatthereisaproblemwithmymethodofdoingwhatwearegoingtodonext.

Youmaynoticethattheonlykindsofreflectionsyouwillreceiveareglobalreflectionsoronesfromthe

HDRI,butnotfromthegeometryitsself.Idevelopedmyownprocessforthis,butitishighly

impractical. IamgoingtotrytoavoidbringingthisupandinsteadwillshowyouanotherprocessthatI

foundonlinefromsomeonemuchsmarterthanmyself. SinceReflectivityisanadditiveprocesswe

dontneedlightsfortheShadertointeractwithHDREnvironmentmap.Soletssetitupourreflections.

Createanewrenderlayer. FormyteapotsceneIonlywantreflectionsontheteapotsthemselvessince

theground

plain

isnt

reflective.

So,

Ihave

only

added

the

teapots

to

my

render

layer.

Next

remember

thereflectionspherewecreatedearlier?Timetoputittouse!Selectthereflectionsphereandaddthat

tothereflectionlayer.GototheattributesofthereflectionlayerandturntheOverrideOnforCast

ShadowandReceiveShadow. Lastbutnotleast,gototheIBLNodesettingsandturnoffEmitlight.

(Figure2.3)


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Figure2.3Nowpressrenderandyoushouldgetsomethinglikethis.(Figure2.4)

Figure2.4Seetheproblem(Figure2.4)?Ido!Howtofixthis?Wellthereare2waystogoaboutthisthefirstwayI

willtrytoexplainasclearlyasIcanandthesecondwayIwillleaveituptoyoutogotoanotherwebsite

forthetutorial.

Thefirstwayistocreateanewrenderlayer.Inthislayeryouneedtoaddeverythingjustasifitwasa

beautypass.Onceyouhavedonethatyouneedtoselecttheobjectthatisgoingtoreceivereflections

forthispass,andaassignablinnmaterialtoit(thiswillbeourreflectionshader).Nowopenthe


14/16

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shadersattributesset:Colortowhite,Diffusetoblack,Ecentricityto0,Reflectionto1andSpecularity

towhite(courtesyofBridgetGaynor).Selecteverythingelseinthesceneandturnofftheprimary

visibility.Thisshouldgiveyouanicereflectionbutwithoutselfreflection(Figure2.5). Ididmanageto

conquertheproblemofnoselfreflectiononapreviousprojectbutinacrudeway.Ifyouwhereto

duplicatethegeometrythatyouhavethereflectionshaderon,placetheoriginalshaderbackonitonit

andjustturntheprimaryvisibilityoffontheduplicationyouwillgetyourselfreflections. (Figure2.6)

Figure2.5

Figure2.6


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Thesecondwaywasdonebysomeonemoreadeptthanme. Byusingsomeofthenewproduction

shaders,thatareunsupportedcurrentlybutcanbeunlocked,wecanremedythesituation.Iamnot

goingtogetintoexplaininghowtodothisinmytutorialbutifyougoto

http://www.djx.com.au/blog/category/tutorialsandgetalltheinformationyouneedfromthisamazing

dude!

Figure2.7
http://www.djx.com.au/blog/category/tutorialshttp://www.djx.com.au/blog/category/tutorials


16/16

BrendanFitzgerald


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Wellthataboutdoesit! Belowisafinalcompositewithalltherenderpassesthatwecreatedhereplus

aOcclusionPass.Ifyouhaveanyquestionspleasefeelfreetocontactmeaswitheverythingthereis

alwaysmoretocover.Hopefullythishelpedandyoulearnedsomethingnew!Rememberbecreative

whentryingtocomeupwithdifferentrenderpassesandkeepthinkingoutsideofthebox.Thereis

alwaysananswer.(Figure2.8)

Figure2.8

Specialthanksto:

AlTorres

KirtWitte

CecilyKamps(Girlfriend/Editor)

BridgetGaynor

(Digital

Lighting

and

Rendering

is

agreat

class!)

AndRemembertheDigitalMediaClubmeetseveryweekonWednesdayinMontgomeryRoom223

from89pm!

www.DMCscad.com

Documents

HDRI and Mental Ray