三维建模外文资料翻译--人体动画基础

外文资料翻译原文部分FUNDAMENTALSOFHUMANANIMATIONFROMPETERRATNER3DHUMANMODELINGANDANIMATIONMAMERICAWILEY,2003243249IFYOUAREREADINGTHISPART,THENYOUHAVEMOSTLIKELYFINISHEDBUILDINGYOURHUMANCHARACTER,CREATEDTEXTURESFORIT,SETUPITSSKELETON,MADEMORPHTARGETSFORFACIALEXPRESSIONS,ANDARRANGEDLIGHTSAROUNDTHEMODELYOUHAVETHENARRIVEDATPERHAPSTHEMOSTEXCITINGPARTOF3DDESIGN,WHICHISANIMATINGACHARACTERUPTONOWTHEWORKHASBEENSOMEWHATCREATIVE,SOMETIMESTEDIOUS,ANDOFTENDIFFICULTITISVERYGRATIFYINGWHENALLYOURPREVIOUSEFFORTSSTARTTOPAYOFFASYOUENLIVENYOURCHARACTERWHENANIMATING,THEREISACREATIVEFLOWTHATINCREASESGRADUALLYOVERTIMEYOUARENOWATTHEPHASEWHEREYOUBECOMEBOTHTHEACTORANDTHEDIRECTOROFAMOVIEORPLAYALTHOUGHANIMATIONAPPEARSTOBEAMORESPONTANEOUSACT,ITISNEVERTHELESSJUSTASCHALLENGING,IFNOTMORESO,THANALLTHEPREVIOUSSTEPSTHATLEDUPTOITYOURANIMATIONSWILLLOOKPITIFULIFYOUDONOTUNDERSTANDSOMEBASICFUNDAMENTALSANDPRINCIPLESTHEFOLLOWINGPOINTERSAREMEANTTOGIVEYOUSOMEDIRECTIONFEELFREETOEXPERIMENTWITHTHEMBENDANDBREAKTHERULESWHENEVERYOUTHINKITWILLIMPROVETHEANIMATIONSOMEANIMATIONPOINTERS1TRYISOLATINGPARTSSOMETIMESTHISISREFERREDTOASANIMATINGINSTAGESRATHERTHANTRYINGTOMOVEEVERYPARTOFABODYATTHESAMETIME,CONCENTRATEONSPECIFICAREASONLYONESECTIONOFTHEBODYISMOVEDFORTHEDURATIONOFTHEANIMATIONTHENRETURNINGTOTHEBEGINNINGOFTHETIMELINE,ANOTHERSECTIONISANIMATEDBYSUCCESSIVELYRETURNINGTOTHEBEGINNINGANDANIMATINGADIFFERENTPARTEACHTIME,THEENTIREPROCESSISLESSCONFUSING2PUTINSOMELAGTIMEDIFFERENTPARTSOFTHEBODYSHOULDNOTSTARTANDSTOPATTHESAMETIMEWHENANARMSWINGS,THELOWERARMSHOULDFOLLOWAFEWFRAMESAFTERTHATTHEHANDSWINGSAFTERTHELOWERARMITISLIKEACHAINREACTIONTHATWORKSITSWAYTHROUGHTHEENTIRELENGTHOFTHELIMB3NOTHINGEVERCOMESTOATOTALSTOPINLIFE,ONLYMACHINESAPPEARTOCOMETOADEADSTOPMUSCLES,TENDONS,FORCE,ANDGRAVITYALLAFFECTTHEMOVEMENTOFAHUMANYOUCANPROVETHISTOYOURSELFTRYPUNCHINGTHEAIRWITHAFULLEXTENSIONNOTICETHATYOURFISTHASABOUNCEATTHEENDIFAPARTCOMESTOASTOPSUCHASAMOTIONHOLD,KEYFRAMEITONCEANDTHENAGAINAFTERTHREETOEIGHTORMOREKEYFRAMESYOURMOTIONGRAPHWILLTHENHAVEACURVEBETWEENTHETWOIDENTICALKEYFRAMESTHISWILLMAKETHEPARTAPPEARTOBOUNCERATHERTHANCOMETOADEADSTOP4ADDFACIALEXPRESSIONSANDFINGERMOVEMENTSYOURDIGITALHUMANSHOULDEXHIBITSIGNSOFLIFEBYBLINKINGANDBREATHINGABLINKWILLNORMALLYOCCUREVERY60SECONDSATYPICALBLINKMIGHTBEASFOLLOWSFRAME60BOTHEYESAREOPENFRAME61THERIGHTEYECLOSESHALFWAYFRAME62THERIGHTEYECLOSESALLTHEWAYANDTHELEFTEYECLOSESHALFWAYFRAME63THERIGHTEYEOPENSHALFWAYANDTHELEFTEYECLOSESALLTHEWAYFRAME64THERIGHTEYEOPENSALLTHEWAYANDLEFTEYEOPENSHALFWAYFRAME65THELEFTEYEOPENSALLTHEWAYCLOSINGTHEEYESATSLIGHTLYDIFFERENTTIMESMAKESTHEBLINKLESSMECHANICALCHANGINGFACIALEXPRESSIONSCOULDBEJUSTUSINGEYEMOVEMENTSTOINDICATETHOUGHTSRUNNINGTHROUGHYOURMODELSHEADTHEHANDSWILLAPPEARSTIFFIFYOUDONOTADDFINGERMOVEMENTSTOOMANYSTUDENTSARETOOLAZYTOTAKETHETIMETOADDFACIALANDHANDMOVEMENTSIFYOUMAKETHEEXTRAEFFORTFORTHESEDETAILSYOUWILLFINDTHATYOURANIMATIONSBECOMEMUCHMOREINTERESTING5WHATISNOTSEENBYTHECAMERAISUNIMPORTANTIFANARMGOESTHROUGHALEGBUTISNOTSEENINTHECAMERAVIEW,THENDONOTBOTHERTOFIXITIFYOUWANTAHANDTOAPPEARCLOSETOTHEBODYANDTHECAMERAVIEWMAKESITSEEMTOBECLOSEEVENTHOUGHITISNOT,THENWHYMOVEITANYCLOSERTHISALSOAPPLIESTOSETSTHEREISNONEEDTOBUILDANENTIREHOUSEIFALLTHEACTIONTAKESPLACEINTHELIVINGROOMCONSIDERPAINTINGBACKDROPSRATHERTHANMODELINGEVERYPARTOFASCENE6USEAMINIMUMAMOUNTOFKEYFRAMESTOOMANYKEYFRAMESCANMAKETHECHARACTERAPPEARTOMOVEINSPASTICMOTIONSSHARP,CARTOONLIKEMOVEMENTSARECREATEDWITHCLOSELYSPACEDKEYFRAMESFLOATYORSOFT,LANGUIDMOTIONSARETHERESULTOFWIDELYSPACEDKEYFRAMESANANIMATIONWILLOFTENBEAMIXTUREOFBOTHTRYTOLOOKFORWAYSTHATWILLABBREVIATETHEMOTIONSYOUCANRETAINTHEESSENTIALELEMENTSOFANANIMATIONWHILEREDUCINGTHEAMOUNTOFKEYFRAMESNECESSARYTOCREATEAGESTURE7ANCHORAPARTOFTHEBODYUNLESSYOURCHARACTERISINTHEAIR,ITSHOULDHAVESOMEPARTOFITSELFLOCKEDTOTHEGROUNDTHISCOULDBEAFOOT,AHAND,ORBOTHWHICHEVERPORTIONISONTHEGROUNDSHOULDBEHELDINTHESAMESPOTFORANUMBEROFFRAMESTHISPREVENTSUNWANTEDSLIDINGMOTIONSWHENTHEMODELSHIFTSITSWEIGHT,THEFOOTTHATTOUCHESDOWNBECOMESLOCKEDINPLACETHISISESPECIALLYTRUEWITHWALKINGMOTIONSTHEREAREANUMBEROFWAYSTOLOCKPARTSOFAMODELTOTHEGROUNDONEMETHODISTOUSEINVERSEKINEMATICSTHEGOALOBJECT,WHICHCOULDBEANULL,AUTOMATICALLYLOCKSAFOOTORHANDTOTHEBOTTOMSURFACEANOTHERMETHODISTOMANUALLYKEYFRAMETHEPARTTHATNEEDSTOBEMOTIONLESSINTHESAMESPOTTHECHARACTERORITSLIMBSWILLHAVETOBEMOVEDANDROTATED,SOTHATFOOTORHANDSTAYSINTHESAMEPLACEIFYOUAREUSINGFORWARDKINEMATICS,THENTHISCOULDMEANKEYFRAMINGPRACTICALLYEVERYFRAMEUNTILITISTIMETOUNLOCKTHATFOOTORHAND8ACHARACTERSHOULDEXHIBITWEIGHTONEOFTHEMOSTCHALLENGINGTASKSIN3DANIMATIONISTOHAVEADIGITALACTORAPPEARTOHAVEWEIGHTANDMASSYOUCANUSESEVERALTECHNIQUESTOACHIEVETHISSQUASHANDSTRETCH,ORWEIGHTANDRECOIL,ONEOFTHE12PRINCIPLESOFANIMATIONDISCUSSEDINCHAPTER12,ISANEXCELLENTWAYTOGIVEYOURCHARACTERWEIGHTBYADDINGALITTLEBOUNCETOYOURHUMAN,HEORSHEWILLAPPEARTORESPONDTOTHEFORCEOFGRAVITYFOREXAMPLE,IFYOURCHARACTERJUMPSUPANDLANDS,LIFTTHEBODYUPALITTLEAFTERITMAKESCONTACTFORAHEAVYCHARACTER,YOUCANDOTHISSEVERALTIMESANDHAVEITDECREASEOVERTIMETHISWILLMAKEITSEEMASIFTHEFORCEOFTHECONTACTCAUSESTHEBODYTOVIBRATEALITTLESECONDARYACTIONS,ANOTHERONEOFTHE12PRINCIPLESOFANIMATIONDISCUSSEDINCHAPTER12,AREANIMPORTANTWAYTOSHOWTHEEFFECTSOFGRAVITYANDMASSUSINGTHEPREVIOUSEXAMPLEOFAJUMPINGCHARACTER,WHENHEORSHELANDS,THEBELLYCOULDBOUNCEUPANDDOWN,THEARMSCOULDHAVESOMESPRINGTOTHEM,THEHEADCOULDTILTFORWARD,ANDSOONMOVINGORVIBRATINGTHEOBJECTTHATCOMESINCONTACTWITHTHETRAVELINGENTITYISANOTHERMETHODFORSHOWINGTHEFORCEOFMASSANDGRAVITYAFLOORCOULDVIBRATEORACHAIRTHATAPERSONSITSINRESPONDTOTHEWEIGHTBYTHESEATGOINGDOWNANDRECOVERINGBACKUPALITTLESOMETIMESANANIMATORWILLSHAKETHECAMERATOINDICATETHEEFFECTSOFAFORCEITISIMPORTANTTOTAKEINTOCONSIDERATIONTHESIZEANDWEIGHTOFACHARACTERHEAVYOBJECTSSUCHASANELEPHANTWILLSPENDMORETIMEONTHEGROUND,WHILEALIGHTCHARACTERLIKEARABBITWILLSPENDMORETIMEINTHEAIRTHEHOPPINGRABBITHARDLYSHOWSTHEEFFECTSOFGRAVITYANDMASS9TAKETHETIMETOACTOUTTHEACTIONSOOFTEN,ITISTOOEASYTOJUSTSITATTHECOMPUTERANDTRYTOSOLVEALLTHEPROBLEMSOFANIMATINGAHUMANPUTSOMELIFEINTOTHEPERFORMANCEBYGETTINGUPANDACTINGOUTTHEMOTIONSTHISWILLMAKETHECHARACTERSACTIONSMOREUNIQUEANDALSOSOLVEMANYTIMINGANDPOSITIONINGPROBLEMSTHEBESTANIMATORSAREALSOEXCELLENTACTORSAMIRRORISANINDISPENSABLETOOLFORTHEANIMATORVIDEOTAPINGYOURSELFCANALSOBEAGREATHELP10DECIDEWHETHERTOUSEIK,FK,ORABLENDOFBOTHFORWARDKINEMATICSANDINVERSEKINEMATICSHAVETHEIRADVANTAGESANDDISADVANTAGESFKALLOWSFULLCONTROLOVERTHEMOTIONSOFDIFFERENTBODYPARTSABONECANBEROTATEDANDMOVEDTOTHEEXACTDEGREEANDLOCATIONONEDESIRESTHEDISADVANTAGETOUSINGFKISTHATWHENYOURPERSONHASTOINTERACTWITHINANENVIRONMENT,SIMPLEMOVEMENTSBECOMEDIFFICULTANCHORINGAFOOTTOTHEGROUNDSOITDOESNOTMOVEISCHALLENGINGBECAUSEWHENEVERYOUMOVETHEBODY,THEFEETSLIDEAHANDRESTINGONADESKHASTHESAMEPROBLEMIKMOVESTHESKELETONWITHGOALOBJECTSSUCHASANULLUSINGIK,THETASKOFANCHORINGFEETANDHANDSBECOMESVERYSIMPLETHEDISADVANTAGETOIKISTHATAGREATAMOUNTOFCONTROLISPACKEDTOGETHERINTOTHEGOALOBJECTSCERTAINPOSESBECOMEVERYDIFFICULTTOACHIEVEIFTHEUPPERBODYDOESNOTREQUIREANYINTERACTIONWITHITSENVIRONMENT,THENCONSIDERABLENDOFBOTHIKANDFKIKCANBESETUPFORTHELOWERHALFOFTHEBODYTOANCHORTHEFEETTOTHEGROUND,WHILEFKONTHEUPPERBODYALLOWSGREATERFREEDOMANDPRECISIONOFMOVEMENTSEVERYSITUATIONINVOLVESADIFFERENTAPPROACHUSEYOURJUDGMENTTODECIDEWHICHSETUPFITSTHEANIMATIONMOSTRELIABLY11ADDDIALOGUEITHASBEENSAIDTHATMORETHAN90OFSTUDENTANIMATIONSTHATARESUBMITTEDTOCOMPANIESLACKDIALOGUETHEFEWTHATINCORPORATESPEECHINTHEIRANIMATIONSMAKETHEIRWORKHIGHLYNOTICEABLEIFTHEANIMATIONANDDIALOGUEAREWELLDONE,THENTHOSEFEWHAVEAGREATERADVANTAGETHANTHEIRCOMPETITIONCOMPANIESUNDERSTANDTHATITTAKESEXTRAEFFORTANDSKILLTOCREATEANIMATIONWITHDIALOGUEWHENYOUPLANYOURSTORY,THINKABOUTCREATINGINTERACTIONBETWEENCHARACTERSNOTONLYONAPHYSICALLEVELBUTTHROUGHDIALOGUEASWELLTHEREARESEVERALTECHNIQUES,DISCUSSEDINTHISCHAPTER,THATCANBEUSEDTOMAKEDIALOGUEMANAGEABLE12USETHEGRAPHEDITORTOCLEANUPYOURANIMATIONSTHEGRAPHEDITORISAUSEFULTOOLTHATALL3DANIMATORSSHOULDBECOMEFAMILIARWITHITISBASICALLYAREPRESENTATIONOFALLTHEOBJECTS,LIGHTS,ANDCAMERASINYOURSCENEITKEEPSTRACKOFALLTHEIRACTIVITIESANDPROPERTIESAGOODUSEOFTHEGRAPHEDITORISTOCLEANUPMORPHTARGETSAFTERANIMATINGFACIALEXPRESSIONSIFTHEDEFAULTINCOMINGCURVEINYOURGRAPHEDITORISSETTOARCSRATHERTHANSTRAIGHTLINES,YOUWILLMOSTLIKELYFINDTHATSOMETIMESSPLINESINTHEGRAPHEDITORWILLCURVEBELOWAVALUEOFZEROTHISCANYIELDSOMEUNPREDICTABLERESULTSTHEFACIALMORPHTARGETSBEGINTOTAKEONNEGATIVEVALUESTHATLEADTOUNDESIRABLEFACIALEXPRESSIONSWHENEVERYOUSEEACURVEBENDBELOWAVALUEOFZERO,SELECTTHEFIRSTKEYFRAMEPOINTTOTHERIGHTOFTHEARCANDSETITSCURVETOLINEARAMOREDETAILEDDISCUSSIONOFTHEGRAPHEDITORWILLBEFOUNDINALATERPARTOFTHISCHAPTERANIMATINGINSTAGESALLTHEVARIOUSCOMPONENTSTHATCANBEMOVEDONAHUMANMODELOFTENBECOMECONFUSINGIFYOUTRYTOCHANGETHEMATTHESAMETIMETHEPERFORMANCEQUICKLYDETERIORATESINTOAMECHANICALROUTINEIFYOUTRYTOALTERALLTHESEPARTSATTHESAMEKEYFRAMESREMEMBER,YOUARETRYINGTOCREATEHUMANQUALITIES,NOTROBOTICONESISOLATINGAREASTOBEMOVEDMEANSTHATYOUCANLOOKFORTHEPARTSOFTHEBODYTHATHAVEMOTIONOVERTIMEANDCONCENTRATEONJUSTAFEWOFTHOSEFOREXAMPLE,THEFIRSTTHINGYOUCANMOVEISTHEBODYANDLEGSWHENYOUAREDONEMOVINGTHEMAROUNDOVERTHEENTIRETIMELINE,THENTRYROTATINGTHESPINEYOUMIGHTDOTHISBYMOVINGINDIVIDUALSPINEBONESORUSINGANINVERSEKINEMATICSCHAINNOWTHATYOUHAVETHEBODYMOVINGAROUNDANDBENDING,CONCENTRATEONTHEARMSIFYOUARENOTUSINGANIKCHAINTOMOVETHEARMS,HANDS,ANDFINGERS,THENROTATETHEBONESFORTHEUPPERANDLOWERARMDONOTFORGETTHEWRISTFINGERMOVEMENTSCANBEANIMATEDASONEOFTHELASTPARTSFACIALEXPRESSIONSCANALSOBEANIMATEDLASTEXAMPLEMOVIESSHOWINGTHESAMECHARACTERANIMATEDINSTAGESCANBEVIEWEDONTHECDROMASCD111ANIMATIONSTAGESMOVIESSOMESAMPLEIMAGESFROMTHEANIMATIONSCANALSOBESEENINFIGURE111THEFIRSTMOVIESHOWSMOVEMENTONLYINTHEBODYANDLEGSDURINGTHESECONDSTAGE,THESPINEANDHEADWEREANIMATEDTHETHIRDTIME,THEARMSWEREMOVEDFINALLY,INTHEFOURTHANDFINALSTAGE,FACIALEXPRESSIONSANDFINGERMOVEMENTSWEREADDEDANIMATINGINSUCCESSIVEPASSESSHOULDSIMPLIFYTHEPROCESSSOMEFINALSTAGESWOULDBEUSEDTOCLEANUPOREDITTHEANIMATIONSOMETIMESTHEANIMATIONSWITCHESFROMONEPARTOFTHEBODYLEADINGTOANOTHERFOREXAMPLE,SOMEWHEREDURINGTHEMIDDLEOFANANIMATIONTHEUPPERBODYBEGINSTOLEADTHELOWERONEINACASELIKETHIS,YOUWOULDTHENSWITCHFROMANIMA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停止。4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。5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。6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。7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。8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。9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。10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动也会有难度因为当你移动身体时，脚就会滑动。放在桌上的手也会有相同问题。IK没有目标的移动骨骼。使用IK，固定脚和手就变得非常简单。其缺点是大部分的控制会被集中到目标位置。某个特定姿势会变得难以实现。如果上身不需要任何与环境的互动，那就考虑IK和FK两者都用。IK可以设置身体的下半部分把脚固定在地上，而上半部分用FK使身体移动的自由度和精确度更好。每种情况都涉及到一种不同的方法。根据自己判断决定哪种设置最可靠地适合动画。11添加对话。曾经有个说法是学生提交给公司的动画中有90以上都缺少对话。只有很少一部分学生在动画中添加了对话，从而极大地提高了作品的吸引力。如果动画和对话配合良好，比起他们的竞争对手，这