三维建模外文资料翻译人体动画基础

FundamentalsofHumanAnimation(FromPeterRatner.3DHumanModelingandAnimation[M].America:Wiley,2003:243~249)Ifyouarereadingthispart,thenyouhavemostlikelyfinishedbuildingyourhumancharacter,createdtexturesforit,setupitsskeleton,mademorphtargetsforfacialexpressions,andarrangedlightsaroundthemodel.Youhavethenarrivedatperhapsthemostexcitingpartof3-Ddesign,whichisanimatingacharacter.Uptonowtheworkhasbeensomewhatcreative,sometimestedious,andoftendifficult.Itisverygratifyingwhenallyourpreviouseffortsstarttopayoffasyouenlivenyourcharacter.Whenanimating,thereisacreativeflowthatincreasesgraduallyovertime.Youarenowatthephasewhereyoubecomeboththeactorandthedirectorofamovieorplay.Althoughanimationappearstobeamorespontaneousact,itisneverthelessjustaschallenging,ifnotmoreso,thanallthepreviousstepsthatleduptoit.Youranimationswilllookpitifulifyoudonotunderstandsomebasicfundamentalsandprinciples.Thefollowingpointersaremeanttogiveyousomedirection.Feelfreetoexperimentwiththem.Bendandbreaktheruleswheneveryouthinkitwillimprovetheanimation.SOMEANIMATIONPOINTERS1.Tryisolatingparts.Sometimesthisisreferredtoasanimatinginstages.Ratherthantryingtomoveeverypartofabodyatthesametime,concentrateonspecificareas.Onlyonesectionofthebodyismovedforthedurationoftheanimation.Thenreturningtothebeginningofthetimeline,anothersectionisanimated.Bysuccessivelyreturningtothebeginningandanimatingadifferentparteachtime,theentireprocessislessconfusing.2.Putinsomelagtime.Differentpartsofthebodyshouldnotstartandstopatthesametime.Whenanarmswings,thelowerarmshouldfollowafewframesafterthat.Thehandswingsafterthelowerarm.Itislikeachainreactionthatworksitswaythroughtheentirelengthofthelimb.3.Nothingevercomestoatotalstop.Inlife,onlymachinesappeartocometoadeadstop.Muscles,tendons,force,andgravityallaffectthemovementofahuman.Youcanprovethistoyourself.Trypunchingtheairwithafullextension.Noticethatyourfisthasabounceattheend.Ifapartcomestoastopsuchasamotionhold,keyframeitonceandthenagainafterthreetoeightormorekeyframes.Yourmotiongraphwillthenhaveacurvebetweenthetwoidenticalkeyframes.Thiswillmakethepartappeartobounceratherthancometoadeadstop.4.Addfacialexpressionsandfingermovements.Yourdigitalhumanshouldexhibitsignsoflifebyblinkingandbreathing.Ablinkwillnormallyoccurevery60seconds.Atypicalblinkmightbeasfollows:Frame60:Botheyesareopen.Frame61:Therighteyecloseshalfway.Frame62:Therighteyeclosesallthewayandthelefteyecloseshalfway.Frame63:Therighteyeopenshalfwayandthelefteyeclosesalltheway.Frame64:Therighteyeopensallthewayandlefteyeopenshalfway.Frame65:Thelefteyeopensalltheway.Closingtheeyesatslightlydifferenttimesmakestheblinklessmechanical.Changingfacialexpressionscouldbejustusingeyemovementstoindicatethoughtsrunningthroughyourmodel'shead.Thehandswillappearstiffifyoudonotaddfingermovements.Toomanystudentsaretoolazytotakethetimetoaddfacialandhandmovements.Ifyoumaketheextraeffortforthesedetailsyouwillfindthatyouranimationsbecomemuchmoreinteresting.5.Whatisnotseenbythecameraisunimportant.Ifanarmgoesthroughalegbutisnotseeninthecameraview,thendonotbothertofixit.Ifyouwantahandtoappearclosetothebodyandthecameraviewmakesitseemtobecloseeventhoughitisnot,thenwhymoveitanycloser?Thisalsoappliestosets.Thereisnoneedtobuildanentirehouseifalltheactiontakesplaceinthelivingroom.Considerpaintingbackdropsratherthanmodelingeverypartofascene.6.Useaminimumamountofkeyframes.Toomanykeyframescanmakethecharacterappeartomoveinspasticmotions.Sharp,cartoonlikemovementsarecreatedwithcloselyspacedkeyframes.Floatyorsoft,languidmotionsaretheresultofwidelyspacedkeyframes.Ananimationwilloftenbeamixtureofboth.Trytolookforwaysthatwillabbreviatethemotions.Youcanretaintheessentialelementsofananimationwhilereducingtheamountofkeyframesnecessarytocreateagesture.7.Anchorapartofthebody.Unlessyourcharacterisintheair,itshouldhavesomepartofitselflockedtotheground.Thiscouldbeafoot,ahand,orboth.Whicheverportionisonthegroundshouldbeheldinthesamespotforanumberofframes.Thispreventsunwantedslidingmotions.Whenthemodelshiftsitsweight,thefootthattouchesdownbecomeslockedinplace.Thisisespeciallytruewithwalkingmotions.Thereareanumberofwaystolockpartsofamodeltotheground.Onemethodistouseinversekinematics.Thegoalobject,whichcouldbeanull,automaticallylocksafootorhandtothebottomsurface.Anothermethodistomanuallykeyframethepartthatneedstobemotionlessinthesamespot.Thecharacteroritslimbswillhavetobemovedandrotated,sothatfootorhandstaysinthesameplace.Ifyouareusingforwardkinematics,thenthiscouldmeankeyframingpracticallyeveryframeuntilitistimetounlockthatfootorhand.8.Acharactershouldexhibitweight.Oneofthemostchallengingtasksin3-Danimationistohaveadigitalactorappeartohaveweightandmass.Youcanuseseveraltechniquestoachievethis.Squashandstretch,orweightandrecoil,oneofthe12principlesofanimationdiscussedinChapter12,isanexcellentwaytogiveyourcharacterweight.Byaddingalittlebouncetoyourhuman,heorshewillappeartorespondtotheforceofgravity.Forexample,ifyourcharacterjumpsupandlands,liftthebodyupalittleafteritmakescontact.Foraheavycharacter,youcandothisseveraltimesandhaveitdecreaseovertime.Thiswillmakeitseemasiftheforceofthecontactcausesthebodytovibratealittle.Secondaryactions,anotheroneofthe12principlesofanimationdiscussedinChapter12,areanimportantwaytoshowtheeffectsofgravityandmass.Usingthepreviousexampleofajumpingcharacter,whenheorshelands,thebellycouldbounceupanddown,thearmscouldhavesomespringtothem,theheadcouldtiltforward,andsoon.Movingorvibratingtheobjectthatcomesincontactwiththetravelingentityisanothermethodforshowingtheforceofmassandgravity.Afloorcouldvibrateorachairthatapersonsitsinrespondtotheweightbytheseatgoingdownandrecoveringbackupalittle.Sometimesananimatorwillshakethecameratoindicatetheeffectsofaforce.Itisimportanttotakeintoconsiderationthesizeandweightofacharacter.Heavyobjectssuchasanelephantwillspendmoretimeontheground,whilealightcharacterlikearabbitwillspendmoretimeintheair.Thehoppingrabbithardlyshowstheeffectsofgravityandmass.9.Takethetimetoactouttheaction.Sooften,itistooeasytojustsitatthecomputerandtrytosolvealltheproblemsofanimatingahuman.Putsomelifeintotheperformancebygettingupandactingoutthemotions.Thiswillmakethecharacter'sactionsmoreuniqueandalsosolvemanytimingandpositioningproblems.Thebestanimatorsarealsoexcellentactors.Amirrorisanindispensabletoolfortheanimator.Videotapingyourselfcanalsobeagreathelp.10.DecidewhethertouseIK,FK,orablendofboth.Forwardkinematicsandinversekinematicshavetheiradvantagesanddisadvantages.FKallowsfullcontroloverthemotionsofdifferentbodyparts.Abonecanberotatedandmovedtotheexactdegreeandlocationonedesires.ThedisadvantagetousingFKisthatwhenyourpersonhastointeractwithinanenvironment,simplemovementsbecomedifficult.Anchoringafoottothegroundsoitdoesnotmoveischallengingbecausewheneveryoumovethebody,thefeetslide.Ahandrestingonadeskhasthesameproblem.IKmovestheskeletonwithgoalobjectssuchasanull.UsingIK,thetaskofanchoringfeetandhandsbecomesverysimple.ThedisadvantagetoIKisthatagreatamountofcontrolispackedtogetherintothegoalobjects.Certainposesbecomeverydifficulttoachieve.Iftheupperbodydoesnotrequireanyinteractionwithitsenvironment,thenconsiderablendofbothIKandFK.IKcanbesetupforthelowerhalfofthebodytoanchorthefeettotheground,whileFKontheupperbodyallowsgreaterfreedomandprecisionofmovements.Everysituationinvolvesadifferentapproach.Useyourjudgmenttodecidewhichsetupfitstheanimationmostreliably.11.Adddialogue.Ithasbeensaidthatmorethan90%ofstudentanimationsthataresubmittedtocompanieslackdialogue.Thefewthatincorporatespeechintheiranimationsmaketheirworkhighlynoticeable.Iftheanimationanddialoguearewelldone,thenthosefewhaveagreateradvantagethantheircompetition.Companiesunderstandthatittakesextraeffortandskilltocreateanimationwithdialogue.Whenyouplanyourstory,thinkaboutcreatinginteractionbetweencharactersnotonlyonaphysicallevelbutthroughdialogueaswell.Thereareseveraltechniques,discussedinthischapter,thatcanbeusedtomakedialoguemanageable.12.Usethegrapheditortocleanupyouranimations.Thegrapheditorisausefultoolthatall3-Danimatorsshouldbecomefamiliarwith.Itisbasicallyarepresentationofalltheobjects,lights,andcamerasinyourscene.Itkeepstrackofalltheiractivitiesandproperties.Agooduseofthegrapheditoristocleanupmorphtargetsafteranimatingfacialexpressions.Ifthedefaultincomingcurveinyourgrapheditorissettoarcsratherthanstraightlines,youwillmostlikelyfindthatsometimessplinesinthegrapheditorwillcurvebelowavalueofzero.Thiscanyieldsomeunpredictableresults.Thefacialmorphtargetsbegintotakeonnegativevaluesthatleadtoundesirablefacialexpressions.Wheneveryouseeacurvebendbelowavalueofzero,selectthefirstkeyframepointtotherightofthearcandsetitscurvetolinear.Amoredetaileddiscussionofthegrapheditorwillbefoundinalaterpartofthischapter.ANIMATINGINSTAGESAllthevariouscomponentsthatcanbemovedonahumanmodeloftenbecomeconfusingifyoutrytochangethematthesametime.Theperformancequicklydeterioratesintoamechanicalroutineifyoutrytoalterallthesepartsatthesamekeyframes.Remember,youaretryingtocreatehumanqualities,notroboticones.Isolatingareastobemovedmeansthatyoucanlookforthepartsofthebodythathavemotionovertimeandconcentrateonjustafewofthose.Forexample,thefirstthingyoucanmoveisthebodyandlegs.Whenyouaredonemovingthemaroundovertheentiretimeline,thentryrotatingthespine.Youmightdothisbymovingindividualspinebonesorusinganinversekinematicschain.Nowthatyouhavethebodymovingaroundandbending,concentrateonthearms.IfyouarenotusinganIKchaintomovethearms,hands,andfingers,thenrotatethebonesfortheupperandlowerarm.Donotforgetthewrist.Fingermovementscanbeanimatedasoneofthelastparts.Facialexpressionscanalsobeanimatedlast.ExamplemoviesshowingthesamecharacteranimatedinstagescanbeviewedontheCD-ROMasCD11-1AnimationStagesMovies.SomesampleimagesfromtheanimationscanalsobeseeninFigure11-1.Thefirstmovieshowsmovementonlyinthebodyandlegs.Duringthesecondstage,thespineandheadwereanimated.Thethirdtime,thearmsweremoved.Finally,inthefourthandfinalstage,facialexpressionsandfingermovementswereadded.Animatinginsuccessivepassesshouldsimplifytheprocess.Somefinalstageswouldbeusedtocleanuporedittheanimation.Sometimestheanimationswitchesfromonepartofthebodyleadingtoanother.Forexample,somewhereduringthemiddleofananimationtheupperbodybeginstoleadthelowerone.Inacaselikethis,youwouldthenswitchfromanimatingthelowerbodyfirsttomovingtheupperpartbeforethelowerone.Theorderinwhichoneanimatescanbeamatterofpersonalchoice.Somepeoplemayprefertodofacialanimationfirstorperhapstheyliketomovethearmsbeforeanythingelse.Followingisasummaryofhowsomeonemightanimateahuman.1.Firstpass:Movethebodyandlegs.2.Secondpass:Moveorrotatethespinalbones,neck,andhead.3.Thirdpass:Moveorrotatethearmsandhands.4.Fourthpass:Animatethefingers.5.Fifthpass:Animatetheeyesblinking.6.Sixthpass:Animateeyemovements.7.Seventhpass:Animatethemouth,eyebrows,nose,jaw,andcheeks(youcanbreaktheseupintoseparatepasses).Mostmovementstartsatthehips.Athletesoftenbeginwithawindupactioninthepelvicareathatworksitswayoutwardtotheextremepartsofthebody.Thiswhiplikeactivitycanevenbeobservedinjustaboutanymundaneact.Itisinterestingtonotethatpeoplewhostudymartialartslearnthatmostoftheirpowercomesfromthelowertorso.Studentsareoftentoolazytomakefingermovementsapartoftheiranimation.Thereareseveralmethodsthatcanmaketheprocesslesstimeconsuming.Onewayistocreatemorphtargetsofthefingerpositionsandthenuseshapeshiftingtomovethevariousdigits.Eachfingerispositionedinanopenandfistlikeclosedposture.Forexample,thesectionsoftheindexfingerareclosed,whiletheothersareleftinanopen,relaxedpositionforonemorphtarget.Thenextmorphtargetwouldhaveonlytheringfingerclosedwhilekeepingtheothersopen.Duringtheanimation,slidersarethenusedtoopenandclosethefingersand/orthumbs.Anothermethodtocreatefingermovementsistoanimatetheminbothclosedandopenpositionsandthensavethemotionfilesforeachdigit.Anytimeyouanimatethesamecharacter,youcanloadthemotionsintoyournewscenefile.Itthenbecomesasimpleprocessofselectingeithertheclosedortheopenpositionforeachfingerandthumbandkeyframingthemwhereveryoudesire.DIALOGUEKnowinghowtomakeyourhumanstalkisacrucialpartofcharacteranimation.Onceyouadddialogue,youshouldnoticealivelierperformanceandagreaterpersonalityinyourcharacter.Atfirst,dialoguemayseemtoogreatachallengetoattempt.Actually,ifyoufollowsomesimplerules,youwillfindthataddingspeechtoyouranimationsisnotasdauntingataskasonewouldthink.Thefollowingsuggestionsshouldhelp.DIALOGUEESSENTIALS1.Lookinthemirror.Beforeanimating,useamirrororareflectivesurfacesuchasthatonaCDtofollowlipmovementsandfacialexpressions.2.Theeyes,mouth,andbrowschangethemost.Thepartsofthefacethatcontainthegreatestamountofmusclegroupsaretheeyes,brows,andmouth.Therefore,thesearetheareasthatchangethemostwhencreatingexpressions.3.Theheadconstantlymovesduringdialogue.Animaterandomheadmovements,nomatterhowsmall,duringtheentireanimation.Involuntarymotionsoftheheadmakeapointwithouthavingtostateitoutright.Forexample,noddingandshakingtheheadcommunicate,respectively,positiveandnegativeresponses.Leaningtheheadforwardcanshowanger,whileadownwardmovementcommunicatessadness.Movetheheadtoaccentuateandemphasizecertainstatements.Listentothewordsthatarestressedandaddextraheadmovementstothem.4.Communicateemotions.Therearesixrecognizableuniversalemotions:sadness,anger,joy,fear,disgust,andsurprise.Other,moreambiguousstatesarepain,sleepiness,passion,physicalexertion,shyness,embarrassment,worry,disdain,sternness,skepticism,laughter,yelling,vanity,impatience,andawe.5.Usephonemesandvisemes.Phonemesaretheindividualsoundswehearinspeech.Ratherthantryingtospelloutaword,recreatethewordasaphoneme.Forexample,thewordcomputerisphoneticallyspelled"cumpewtrr."Visemesarethemouthshapesandtonguepositionsemployedduringspeech.Ithelpstremendouslytodrawachartthatrecreatesspeechasphonemescombinedwithmouthshapes(visemes)aboveorbelowatimelinewiththeframesmarkedandthesoundandvolumeindicated.6.Neveranimatebehindthedialogue.Itisbettertomakethemouthshapesoneortwoframesbeforethedialogue.7.Don'toverstate.Realisticfacialmovementsarefairlylimited.Themouthdoesnotopenthatmuchwhentalking.8.Blinkingisalwaysapartoffacialanimation.Itoccursabouteverytwoseconds.Differentemotionalstatesaffecttherateofblinking.Nervousnessincreasestherateofblinking,whileangerdecreasesit.9.Movetheeyes.Tomakethecharacterappeartobealive,besuretoaddeyemotions.About80%ofthetimeisspentwatchingtheeyesandmouth,whileabout20%isfocusedonthehandsandbody.10.Breathingshouldbeapartoffacialanimation.Openingthemouthandmovingtheheadbackslightlywillshowanintakeofair,whileflaringthenostrilsandhavingtheheadnodforwardalittlecanshowexhalation.Breathingmovementsshouldbeverysubtleandhardlynoticeable...外文资料翻译—译文部分人体动画基础(引自PeterRatner.3DHumanModelingandAnimation[M].America:Wiley,2003:243~249)如果你读到了这部分，说明你很可能已构建好了人物角色，为它创建了纹理，建立起了人体骨骼，为面部表情制作了morph修改器并在模型周围安排好了灯光。接下来就是三维设计中最精彩的部分，即制作角色动画。到目前为止有些工作极富创意，有些枯燥乏味，但都困难重重。在经过了前期的努力后，角色已显示出了活力，这是非常令人高兴的。在制作动画时，创意会随着时间的推移不断涌现。现在你既是电影和戏剧的演员又是导演。虽然动作是很自然的表演，但它即使不比之前的准备步骤更复杂，也极具挑战。如果你不懂一些基础知识和基本原理，制作出的动画会很可笑。以下几点为你提供一些指导。尽管拿它们做实验。只要你认为能改进动画，可随意遵守或打破这些规则。动画指南：尝试分离各部分。有时指的是分阶段制作动画。不要试图同时移动身体的每个部位，应集中精力制作具体部位的动画。在动画的持续时间内只移动身体的一部分。然后返回时间轴的起始位置，制作另一部分的动画。通过不断回到起始位置，每次制作一个不同部位的动画，能使整个过程变得清晰明了。添加一些延迟。身体的不同部位不应该同时开始和停止动作。当胳膊摆动时，下臂应该在其随后摆动几帧。在下臂停止摆动后手再摆动。整个手臂的活动就像是一边连串的连锁反应。任何一个动作都不会戛然而止。生活中，只有机器会突然停止。肌肉，腱，压力和引力都会影响人体的移动。你可以亲自证明这一点。用力向前推拳直到完全舒展开手臂。注意最终你的拳头会回弹一下。如果一个部位要停止，例如要保持动作，首先把它设置为关键帧，然后在3到8个或更多关键帧后再设置一次关键帧。动作图形会在两个相同的关键帧中间产生一条曲线。这会使动作有一个回弹而不是马上停止。添加面部表情和手指动作。数字人体应当通过眨眼和呼吸来呈现生命的气息。通常每隔60秒会眨一下眼睛。典型的眨眼应该如下所述：第60帧：两眼都睁开。第61帧：右眼半合。第62帧：右眼紧闭，左眼半合。第63帧：右眼半睁，左眼紧闭。第64帧：右眼完全睁开，左眼半睁。第65帧：左眼完全睁开。在不同时间闭上眼睛会让眨眼显得更为自然。面部表情的改变可通过眼睛的转动来表明模型脑海中的想法。如果你不添加手指动作，手会显得过于僵硬。很多同学懒得花时间去添加面部和手部动作。如果你花额外的努力在这些细节上，你的动画会变得更有趣。摄像机没有拍到的内容不用关注。如果胳膊叉到了腿里但摄像机视图中看不到，就不用费心去更正。如果你希望一只手看上去靠近身体并且摄像机视角看上去也是如此，即使实际并不靠近，也没必要再做调整。这也适用于布景。如果所有的表演都发生在起居室，就没必要建造整幢房子。考虑绘制背景而不是做出场景每一部分的模型。尽量少使用关键帧。过多的关键帧会让角色动作看上去有痉挛的感觉。剧烈，类似于卡通的动作是使用分布密集的关键帧制作的。飘逸或柔和、没精打采的动作是通过分布稀疏的关键帧制作的。动画中通常结合使用二者。试着寻找可以简化动作的方法。你可以在保留动画基本元素的同时减少构成姿势所需的关键帧数量。通过锁定位置锚定身体的某个部位。除非你的角色在空中，否则它身体的一些部位应该被锁定在地面上。可以是一只脚，一只手或二者。处于地面的部分应该在好几帧上保持在同一位置。这样可阻止不必要的滑动。当模型移动重量时，落下的脚被锁定在适当的位置。对于行走动作这点特别适用。有很多方法将模型的部位锁定在地面上。除了直接把一只脚或一只手锁定在地面外，另一种方法是把需要保持在相同位置的部位手动变成关键帧。角色或其四肢必须移动或旋转，只有这样，脚可手才能保持在相同位置。角色应该显示重量。三维动画中最富挑战性的一项任务是让一个数字演员显得拥有重量和质量。可以使用几种方法来实现。第12章中讨论的动画的12个原理之一的挤压与拉伸（或者重量与反弹）是为角色提供重量的好方法。通过为人体添加一些反弹动作，可以展示角色受到重力影响的效果。比如，如果角色跳起后落下，脚触地后身体要稍微向上抬一下。对于一个比较重的角色，可以让这个动作重复几次，一次比一次弱。这显示出接触的力量似乎让身体微微有些振动。第12章中讨论的动画的12个原理中的另外一个——辅助动作是显示重量和质量效果的一种重要方法。就用前面跳跃的角色例子，角色着地时，腹部可以上下颤动，胳膊可以微微弹起，头可以向前倾斜等。移动与正在移动的实体接触的物体或让其振动是另一种显示质量和重力的方法。地板可以振动，有人坐进去的椅子通过下陷再稍微弹回也可以显示出对重量的反应。有时动画师可以晃动摄像机来表明力量的效果。考虑角色的大小和重量很重要。较重的物体如大象大部分时间都在地面上，而较轻的角色如兔子大部分时间在空中。忙碌的兔子很难显示出重力和质量的效果。花时间表演动作。我们很容易只是坐在电脑前，努力解决人体动画的所有问题。站起来，实际表演一下动作，会给动画注入活力。这会让角色的动作显得更为独特，也可以解决许多时间和位置安排问题。最好的动画师也是最优秀的演员。对于动画师来说，镜子是不可或缺的工具。录制自己的表演也有很大的用处。决定是否使用IK，FK，或两者都用。正向运动和逆向运动各有其优缺点。FK能控制不同身体部位的运动。一个骨骼可被旋转移动到想要的精确位置和程度。使用FK的缺点是当你的角色处在一个互动的环境内，简单的移动也会变得困难。当你把脚固定在地面上让它不