RetopologizingVRandGameAssetsUsingBlender*

Thisarticlecovershowtobothretopologizeameshtoaclean,low-densitymodel,andthenUVunwrapthatmeshtosupportaddingtexturemapstothenewmodel.ItalsodiscussestheuseoffreetoolslikeBlender*anditsBSurfaceadd-onforretopologizingasculpted3Dmesh.

AboutRetopology

Retopologyistheactofrebuildinga3Dmeshsoit'slowerinsizeanddesignedcleanerforuse.Retopologymayseemlikejustbusyworkinthe3Dcreator’sprocess,butitisakeytaskandalsoallowsflexibilityinworkingwithyourmodels.Mostoriginalmeshes,builtusing3Dmodelers,sculpted,orscanned,capturealevelofdetailtomakethemodellookgood.Howeverthatsamedetailcreatesalargefilethatisdifficultonreads,writes,andmemoryforyourtargetapplication.Also,mosthighlydetailedmeshescanhavetoomuchdetailorbenonsymmetrical,creatingoddorunwantedcreases,folds,andmovementwhenanimatingthemesh.

Toavoidthis,you’llneedtoretopologizethemeshtoamorebasic,usablestructure,andthentransferthedetaileddataaboutthecolor,bumps,andcreasesoutofthe3Dstructureandinto“baked”2Dmaterialsmaps.Thisallowsthe3Dmeshtobeamuchsmallerfilewithfewervertices,yetproducethesameresultsinrendering.Intheimagesabove,theoriginalmeshwasreducedfrom500,000facesto2,000faces,yettheoutputlooksrelativelythesame.

Whatyouneedtogetstarted:

• PC,Mac*,orLinux*computer;Intel®Core™i5ori7processorrecommended• Blender3DwiththeBSurfaceadd-onenabled(freetodownload)

Blender*andBSurface

Blenderisafree,full-purpose3Dmodeling,rendering,andanimationstudio.Withthispowerfultool,youcancreatesimple3Dobjectsorproduceafull-featuredanimatedfilminBlender.ForthepurposeofthisexercisewefocusonthemodelingsideofBlender.IfyouhaveneverusedBlenderbefore,IsuggestwatchingthisgettingstartedvideotolearnhowtosetupBlenderforgoodresults.

Video:https://www.youtube.com/watch?v=dg6HyERe0Qg&t=503s

Todotheworkinthistutorialyouwillneedahightopology3Dmesh.ForinstructionalpurposesweusedtheSuzannemonkeyheadmodelthatisameshobjectinBlender.Tocreateahigherdensityversionofthismodel,onewithover500Kvertices,followthesesteps.

1. AddMesh,andthenselectSuzanne.2. UndertheToolspanel,selectSmooth.3. UnderthePropertiespanel,clickthewrenchicontogettomodifiers.4. AddthemodifiercalledSubdivisionSurface.5. SetSubdivisionto5.6. ClickApply.

RetopologyUsingBSurface

Thefollowingretopologystepsarecoveredinthisvideo:https://www.youtube.com/watch?v=9tWeZLSXBYc&t=6s

SettingupBSurface

ToinstallBSurface,fromtheFilemenu,clickUserPreferences.SelecttheAdd-Onstab.Searchfor“bsurf”.Ontherighttheadd-onforBSurfacewillappear.Toenable,checktheboxtotheleftofitsname..BSurfaceshouldnowbeinstalledandenabled.

InorderforBSurfacetoplaceverticesintherightplacelinedupwiththeoriginalmodel,you’llneedtohavetheoriginalmodelloadedandinitiallyselectedwhileinObjectModeinthescene.Thentocreateyourretopology,addaplane,whichcreatesanewasset.GototheEditmenu,andthenselectSnaptoFeatures.

ToconfigureBSurface,fromtheToolsmenu,selecttheGreasePenciltab.Thendothefollowing:

• SelectContinue.• UnderDataSource,selectObject.• UnderStrokePlacement,selectSurface.

Youmayfindyoucanmovesomeofthevertices,edges,orfacesaroundmanually.Togetthoseitemstoalsoclingtothesurfaceofyourmodel,selectthefollowingwhileinEditmode:UnderSnap,selecton,andthenunderSnapElement,selectFace.Finally,clickthenextfouriconsonthebottomright.

YouarenowreadytouseBSurface.

Creatingyourfirstgridmesh

BSurfaceautomaticallycreatesameshbasedonafewlinesyoudrawovertheoriginalmesh.

• Youonlyneedtodrawafewparallellinesinonedirection.BSurfacewillcreateacrossingmeshbasedonthoselines.Donotdrawlinesfromdifferentdirectionsorincrossingdirections.

• IntheToolstabundertheToolspanel,youwillseeBSurface.ClicktheAddSurfacebutton.

• Toadjustwhathasbeencreated,setthenumberofCrossstrokesorFollow(linesbetweenthelinesyoudrew).YoucanalsoclearLoopsonstrokesifyouwantBSurfacetoignoreallbutthefirstandlastlinesyoudrew.Followwillnowbesubdivisionsbetweenthefirstandlaststroke.

Creatingaradialmesh

Oftenyouneedameshthatcirclesaroundanarealikeaneyeormouth.Tocreatethesetypesofmeshes,simplydrawevenlyspacedradiallinesfromtheareayouarecircling.

ClickAddSurface,andthenselectCycleCrosstoclosetheradialandsetthenumberofcyclecrossesneeded.

Asbefore,clearLoopsonstrokestosetthesubdivisionsmoreevenly.

CornerFill

Youwillfindyouoftenhavetwosidesofameshcompleted,butyoustillneedtofillthemeshbetweenthem.Todothat,selectallthepointsonthetwosides.UseSHIFT+RIGHT+CLICKtounselectthepointinthecorner,andthendrawoneofthemissingsides.Intheexamplebelowthetopandrightedgesweresetandselected.Abottomedgewasdrawn,followingthecurveofthemeshpoints.ClickAddSurfacetofillitin.

ConnectingMeshes

Toconnecttwomeshes,selectallthepointsyouneedtoconnect.Besureyouhaveselectedthesamenumberofpointsoneeachside.Thenimagineaseriesoflinesbetweenthem.Drawatleasttwoofthoselineswiththelastlinedrawingoveronesetofhighlightedvertices.

YounowhavethebasicsofBSurfaceneededtoquicklyretopologizeamodel.ContinuetouseBSurfacetocreateafullmeshoveryourhightopologymodel.

UVUnwrappingandAddingDetailedTextureMaps

UVunwrappingisakeypiecetotheprocessandisapartofthepipelinethatallowsyoutogetdetailslostfromyourhightopologymodelontoyournewlyretopologizedmodel.

UVunwrappingistheprocessofdefininghowa2Dimagewillbemappedoveralltheverticesinthemesh.Imagineaworldglobewhereyouhaveasmoothsphereandplantohaveaprintedimageoftheglobe’sfeatureswrappedontotheglobe.Forthe2Dimagetowrapovertheglobe,youwillneedtomakecutsintotheimageinawaythatallowsthatimagetowrapproperlyoverasphere.Thisiscalledamapprojection.

sourcewikipedia

For3Dmodeling,UVunwrappingofamodelallowsyoutodefinethisprojectionpattern,whichworksasaguideforallsortsof2Dinformationtobemappedoverthe3Dobject.Intheglobeexample,youcouldbakeinformationinto2Dimagemapsforthecolor,roughness/gloss,andheightinformationforthelandorwateroftheearth,andthenhavethatprojectedontothesphereusingtheUVmap.

BelowisanexampleofaUVmapofa3Dalienheadmodel.Theleftimageiscalledacolormap,andthemiddleimageiscalledanormalmaporbumpmap.Bothimageshaveawireframemeshflattenedoutovertherespectiveimages.ThisflattenedoutmeshpatternistheUVmap.

Whatyouneed

Forthispartofthetutorial,youneedahighpolymeshwithtexturedetails,whichisafileyoucanuse,oralternativelyyoucantakethehighpolyobjectyoucreatedandaddedtexturedetailsusingSculpt.Thelinkedfileisanexampleofthemonkeyheadsculptedwithwrinklesandlinesandskinfolds.

Firstbesurethehighpolymeshandtheretopologyorlowpolymeshareinthesamespace.SettheirX,Y,andZcoordinatestothesamelocationusingthetranslateoptionsinthepropertiespanel.

Thestepsthatfollowarealsocoveredinthisvideo:https://www.youtube.com/watch?v=ouZB0GqF9PU

Step1:MarkingSeams

Marketingseamsistheprocessofselectingwherethemeshwillcutorbreakapartinordertobeaflat2Dpatternofthe3Dmodel.Thinkofseamslikeseamsonashirtorplushtoy,wherethe2Dmaterialwillbestitchedtogether.Andlikethoseseamsyouwouldn’twanttoomanyofthem,norwouldyouwanttoputseamsinhighlyvisibleareas.Putthemwherethereisalotofgeometrythatcurvesaroundandwhereitmakessensetohavenaturaledges.Whenbakingtexturemapsaswearedoing,theseamswilllikelynotshow.Howeverifyouuseproceduralmapsofnoiseorotherpatterns,thosepatternswilloftenbreakattheseams.

Tomarkyouseams,selectyourLowPolyObject,andthengotoEditmode.SelecttheEdgeselectiontool,andthenselectwhereyouwantyourseamstogo.

• SelectMeshMenu>Edge>MarkSeams.Dothisforeveryseamyouwanttomark.

Seamswillappearasred-colorededgesonyourmodel.

Step2:UnwraptheLowPolyMesh

Thisstepisstraightforwardandconsistsofunwrappingthemodel,andthencreatingatexturefiletobemapped.AgainyouneedtobeinEditmodeofyourlowpolymodel.Selectall,verifyingthateverymeshfaceisselected.Type“U”tobringuptheUnwrapmenu.SelectUVUnwrapatthetopofthemenu.

FortheUVmaptowork,you’llwantitasaguideforatexturefileyouaregoingtobakeorrender.CreateanewviewportwindowandsetthatviewporttoUVImageEditor.UnderImageinthatviewportselectNewImage.

Setanydesiredresolutionoptions,giveitaname,andthensave.

Itshouldnowbeablackimagewithnothinginit.YouhowevercanseetheUVmapovertheblackimage.

Step3:BakeaNormalMapoftheHighPolyMesh

Inthisstep,youwill“bake”thetextureinformationonyourhigh-resolutionmodeltoa2Dimagefilecalledanormalmap.Thistexturewillthenbeaddedtothematerialonyourlow-resolutionmodel.Thefirststepistomakesureyourlow-resolutionmodelhasamaterialwithatextureinit.

Selectyourlow-resolutionorretopologymodel.InthePropertiespanelgototheMaterialstab.Ifamaterialdoesn’talreadyexist,addamaterialandselectNodes.(BesureyourrendersettingsatthetopoftheBlenderapplicationaresettoCyclesRender.)

OpentheNodeEditorbysettingoneofyourviewportstoNodeEditor.FromtheAddmenu,selectTexture,andthenImageTexture.

Withthisadded,setthefiletothenameoftheUVimageyoucreatedintheprevioussection.AlsosetittoNon-Colordata.

Nextyouneedtoselectthebakesettings.UnderthePropertiesPanel,selecttheRendersetting,whichisthecameraicon.ScrolltothebottomtotheBakesectionanddothefollowing:

• ForBakeType,selectNormal.• ForSpace,selectTangent.• SelectSelectedToActive.• SetRayDistancetobeatleast1.00.

Thenextpartcanbetricky.Youneedtoselectbothmodels,butyoualsoneedtobesuretofirstselectthehigh-resversion,andthenthelow-resversion.BesureyouareinObjectModeandnotEditMode.

OnceinObjectmode,usingtheAssetInventorypanel,verifythatboththehightopologymodelandthelowtopologymodelarevisibleandhavetheeyeiconstotherightoftheirnames.Selectthehightopologymodelsoitappearsinwhite.Right-clickit,andthenclickSelect.Youshouldseethemodelselectedingoldwithitsnameinthe3DViewport.

NowpressandholdtheSHIFTkey,andthenright-clickthelowpolymodelinthe3Dviewport.Thisactioncausesthenameofthelowpolymodeltonowappearinwhite,thelowpolymodelwillbenamedinthe3Dviewport,andtheselectioncolorwillchangefromgoldtoorange.Withthatdone,clickBakeintheRenderpanel.

Step4:Applythenormalmaptoyourmodel

Inthisfinalstepwetakethebakedfileandconnectittothematerialofourlowpolymodel.Firstyou’llneedtosavetheBakedrenderfromthelaststep.Inyourviewport,undertheUVimagemap,firstverifythatthenameofyoursavedUVmapislistedinthefilebrowser.Theimageshouldbeshadedblue/purple,similartotheimageshownbelow.TheimageontheleftshowsthenormalmapwheninEditmode;theimageontherightshowsthebakedimagewhileinObjectMode.WhileintheUVMapImageeditor,selecttheImageMenu,andthenclickSave.

Wearenowreadytoconnectthistexturetoourmodel.

GototheNodeEditorwhereyouhavetheTextureImageNode.ConnecttheTextureNodetoaNormalMapNode.YoucangetthisNormalMapNodeundertheAdd>Vector>NormalMap.

ConnecttheNormalMapModeintotheNormalslotonthePrincipledBSDFShader.Youshouldnowseeallthedetailsfromyourhigh-resolutionmodelinyourlow-resolutionmodel.

Youhavenowcompletedamajorpartofthe3Dassetworkflowforuseingamesorvirtualrealitysoftware.Inadditiontotexturingnormalinformationonamodel,youcantexturewithothermaterialmapsthatcreaterealisticskin,hair,orothermaterialsfromcrackedconcretetoscratchedgunmetal.Forreferenceonthisnextworkflow,doawebsearchonPBRmaterialsusingtoolslikeSubstancePainter*andBlender.

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