Writing to the OpenGL Stencil Buffer - Stack Overflow

The stencil buffer is theoretically a buffer like the back buffer and the depth buffer. The three of them are written to at the same time (when ... 2022DeveloperSurveyisopen!Takesurvey. Home Public Questions Tags Users Companies Collectives ExploreCollectives Teams StackOverflowforTeams –Startcollaboratingandsharingorganizationalknowledge. CreateafreeTeam WhyTeams? Teams CreatefreeTeam Collectives™onStackOverflow Findcentralized,trustedcontentandcollaboratearoundthetechnologiesyouusemost. Learnmore Teams Q&Aforwork Connectandshareknowledgewithinasinglelocationthatisstructuredandeasytosearch. Learnmore WritingtotheOpenGLStencilBuffer AskQuestion Asked 4years,4monthsago Modified 1year,1monthago Viewed 6ktimes 7 1 I'vebeenreadingaboutthestencilbufferinOpenGL.Thebasicconceptmakessense;afragmentisonlydrawnifitmeetsacertainconditionafterbeingbitwiseANDedwithavalueinthestencilbuffer.ButonethingIdon'tunderstandishowyouactuallywritetothestencilbuffer.IsthereafunctionthatI'mmissinghere? P.S.WhenIsaywrite,Imeanspecifythespecificvaluesinthestencilbuffer. c++openglglfwstencil-buffer Share Follow askedJan14,2018at2:54 papermanpaperman 45644silverbadges1717bronzebadges 7 Readthis:learnopengl.com/#!Advanced-OpenGL/Stencil-testing – FrancisCugler Jan14,2018at3:09 WritingtostencilbufferisdonebythesamefunctionswhichwritetoRGBand/ordepth.ThisishowIexplainedafriend:stenciltesttestissomehowlikedepthtest.Youcandisableitatall.Youcanwriteonly(withouttesting).Youcanenabletesting(andoverwriteincase). – Scheff'sCat Jan14,2018at7:30 @ScheffhowwouldIwritetothestencilbufferwithoutdrawinganythinginthecolorbuffer? – paperman Jan14,2018at13:10 @Scheffnevermind,IthinkIgotit – paperman Jan14,2018at13:12 I'mnotsurewhetheryoucanwritetostencilbufferonly.Ijusthadalookintocodewhereweusedstencilforvertical/horicontalinterlacedstereorendering.(Thestencilbufferisinitiallywrittenwithaline/nolinepatterntorestricttherenderingtotheappropriateevenoroddrows/columns.)IbelieveitjustrendersRGBaswellbutyouwon'tseeit.Itisoverriddenbythefollowingrenderingwhichpassesthestenciltest(andbeforethefinalglSwap()iscalled). – Scheff'sCat Jan14,2018at15:39  |  Show2morecomments 3Answers 3 Sortedby: Resettodefault Highestscore(default) Datemodified(newestfirst) Datecreated(oldestfirst) 9 Nobodyansweredthisquestionandit'savalidquestion,somorethanayearlater,here'sananswertoyourquestion. Thestencilbufferistheoreticallyabufferlikethebackbufferandthedepthbuffer.Thethreeofthemarewrittentoatthesametime(whenenabled).Youcanenable/disablewritingtothemwithspecificcalls: glColorMask(red,green,blue,alpha)-forthebackbuffer glDepthMask(t/f)-forthedepthbuffer glStencilMask(value)-forthestencilbuffer Forthedepthandstencilbuffer,youcanspecificallyenable/disablefurtherwith: glEnable/glDisable(GL_DEPTH_TEST) glEnable/glDisable(GL_STENCIL_TEST) Anytriangleyourendertothescreenwillwritetoallenabledbuffersunlesssomeoperationfunctionalitypreventsit.Forthestencilbuffer,thesecanbesetwithseveralfunctions.PleaselookupthefunctionalitiesontheOpenGLreferencepages,buthereisasimpleexampleofmaskingapartofthescreenandthenrenderingonlyonthatmaskedpartofthescreen,justtogetyoustarted. glClearColor(0,0,0,1); glClearStencil(0); glStencilMask(0xFF); glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT|GL_STENCIL_BUFFER_BIT); glColorMask(GL_FALSE,GL_FALSE,GL_FALSE,GL_FALSE);//Donotdrawanypixelsonthebackbuffer glEnable(GL_STENCIL_TEST);//EnablestestingANDwritingfunctionalities glStencilFunc(GL_ALWAYS,1,0xFF);//Donottestthecurrentvalueinthestencilbuffer,alwaysacceptanyvalueontherefordrawing glStencilMask(0xFF); glStencilOp(GL_REPLACE,GL_REPLACE,GL_REPLACE);//Makeeverytestsucceed //...hereyourenderthepartofthesceneyouwantmasked,thismaybeasimpletriangleorsquare,orforexampleamonitoronacomputerinyourspaceship... glStencilOp(GL_KEEP,GL_KEEP,GL_KEEP);//Makesureyouwillnolonger(over)writestencilvalues,evenifanytestsucceeds glColorMask(GL_TRUE,GL_TRUE,GL_TRUE,GL_TRUE);//Makesurewedrawonthebackbufferagain. glStencilFunc(GL_EQUAL,1,0xFF);//Nowwewillonlydrawpixelswherethecorrespondingstencilbuffervalueequals1 //...hereyourenderyourimageonthecomputerscreen(orwhatever)thatshouldbelimitedbythepreviousgeometry... glDisable(GL_STENCIL_TEST); NotethatIomittedanydepthcodeonpurposetomakesureyouseethatithasnothingtodowithstencilling.Ifyourender3Dgeometry,youmightneedtoenableit.YoumayevenneedtoNOTwriteastencilvalueifadepth-testfails. Notethatitisimportantthatwhenyourenderthemaskinggeometry,yousetthestencilfunctoGL_ALWAYS,becauseotherwise,thecurrentvalueinthestencilbuffer(whichwasclearedintheexample)istestedagainstwhateverwaslastusedandyourmaskinggeometrymaynotevenbedrawnatall. Sotherearenospecialfunctionstowritetothestencilbuffer.I'mnotevensureifitcanbewrittentolikeyoucanwritedatadirectlyintothebackbufferandthedepthbuffervideomemory,butthat'snotthewayitshouldbedoneanyway(becauseit'sterriblyslow).Thestencilbufferismemorysharedwiththedepthbuffer,soitmightbepossiblebychangingtheparametersofthewritefunctions.Iwouldn'tcountonitworkingonallvideodriversthough. Goodlucktoanyonewhoneededthisinformation! Share Follow editedApr9,2021at7:04 answeredSep15,2019at14:52 scippiescippie 1,88411goldbadge2424silverbadges3838bronzebadges 6 wowit'sbeenoverayearandhalfsinceIaskedthisquestion!IwasabletounderstanditeventuallybutIappreciatethatyoustillwroteananswerforanyoneelsewhocomesacrossit:) – paperman Sep16,2019at4:01 Thanksforacceptingit:-).Iknowfromexperiencethatyouarenottheonlyonewhostruggledwiththis,andthat'swhyIsharetheanswer. – scippie Sep16,2019at6:49 Youmentionthatyoucanwritetothestencilbufferaswithanormalbuffer,butI'mnotseeinghowyoucanbindthestencilbuffersothatglBufferDatawillwritetoit.glBindBufferwantsa"name"(Idon'tknowwhyonearththeycallanumberaname)createdbyglGenBuffers,whichdoesn'tseemapplicabletothestencilbuffer. – TrevorGiddings Apr6,2021at5:09 No,itdoesn'tworklikethat@TrevorGiddings,youmustlookatthestencilbufferasanextensiontothecurrentlyselectedrendertarget(whichcansimplybethebackbuffer),whateverhappensonthattarget,willhappenonthestencilbufferifenabledlikeI'veshowninmypost.Ifyouneedtodothiswithoutactuallychangingthatrendertarget,youdisablethecolorwrites(likeintheabovepost).Youcan'tsetthestencilbufferasarendertarget,that'snotpossible.Youshouldlookatitasifitisacarboncoatedpaperyouconnecttotherendertarget. – scippie Apr7,2021at7:18 @scippieifyoucanonlywritetoitbyrenderingtoit,thenIdon'tunderstand"wellnodifferentthanonanyotherbuffersthatis",andIdon'tseehow"Youcouldofcoursereallysendpixeldatatothegraphicalmemory"--unlessyoucountsendingatexturethatwilllaterbyusedwhenrenderingafull-screenquad. – TrevorGiddings Apr8,2021at4:12  |  Show1morecomment 0 Youcanread,writeandcopyvalues(bytes,floats,dwords...)totheframeanddepthbufferbutnottothestencilbuffer. AllthreebuffersarelocateattheGPUmemorytheproblemarethestencilbufferusedtheremaining8bitsfromthe24bitdepthbuffer! Thisiswhyyoumustrendersomethingtosetoroverwritevaluesinthe8bitstencilbuffer(inrealaregioninthedepthbuffer) DJ Share Follow answeredApr4,2021at11:35 DJLinuxDJLinux 1 Addacomment  |  -3 IdescribedhowtorendertoastencilbufferhereusinglibGDX.TheprocessforapplyingamaskinOpenGListhesameregardlessofOpenGLversionorplatform. HowmaskingworksinOpenGL TherearemanywaystocreateamaskinOpenGL,notethatthecodetocreatethemaskinmypreviousansweractuallyusesthedepthbuffer.Icouldhaveusedthestencilbufferinasimilarwaytoachievethesameresult. Usingthedepthbuffer,youcanapplymasksinthefollowingway: Initialiseandconfiguredepthtesting Startbyclearingthedepthbufferanddisablerenderingtothecolorbuffer: glClearDepthf(1.0f); glClear(GL_DEPTH_BUFFER_BIT); glColorMask(false,false,false,false); Next,specifythecriteriaforthebuffer,thistellsOpenGLhowtorendertothedepthbuffertocreatethemask.YoudothisbymakingacalltoglDepthFunc(shouldthemaskedareabetheareaofthescenewheretheshapeisdrawnorshouldsomethingelse?forthedifferentkindsofinputtothedepthfunction,seetheDepthtestsectionofthissite) glDepthFunc(GL_LESS); glEnable(GL_DEPTH_TEST); glDepthMask(true); //Yourcodetorenderthemaskgoeshere Creatingthemask Afterenablingthebuffer,yourenderpolygonsintheshapethatyouwantforthemask.Becausewedisabledwritingtothecolorbuffer,therenderedimagewillnotbevisibleonscreen,itisrenderedtothedepthbuffer.Thedepthbufferhasthesamewidthandheightdimensionsasthecolorbufferbutconsistsof0and1values.Eachpixelhasthedepthtestappliedtoit,ifitpassesthenavalueof1isplacedinthebufferforthatlocation,otherwisethecorrespondinglocationhasavalueof0. Enablecolorbuffer,setdepthfunctionandrendertothescene NowyouconfigureOpenGLtorendertothecolorbufferandapplythedepthmasklikeso: glColorMask(true,true,true,true); glDepthMask(true); glDepthFunc(GL_EQUAL); //Yourcodetorenderthescenegoeshere Sinceyouhavethedepthbufferenabled,everypixelintheviewportwillhaveacorresponding0or1value.Nowanotherdepthfunctionisappliedtothecorrespondingvalueforeachpixelandiftheresultistrue,thepixelisrenderedtothescreen.Herethechoiceofdepthfunctiondetermineshowthemaskisapplied. Disabledepthtesting Toallownormalrenderingtothesceneagain,youdisablethedepthbufferlikeso: glDisable(GL_DEPTH_TEST); Share Follow editedJan15,2018at13:20 answeredJan15,2018at12:02 sparkplugsparkplug 1,45944goldbadges1818silverbadges2121bronzebadges 2 3 Title:WritingtotheOpenGLStencilBuffer,answer:WritingtotheOpenGLDepthBuffer.Ilearnedhowtowritetodepthbufferbutthat'snotwhatIexpectedwhenclickingonquestiononsuchtitleandIstillhaven'tsolvedmyproblem. – PurpleIce Oct27,2018at17:10 Thisisprettyancient,butONEofthebestdiscussiononstencil/depth.Unfortunately.perlast"answer"itisstillmissingrelationsbetweenstencilanddepthbuffers-theyareNOTsame!Accordingthemanydoc-stenciliispecialcaseofdepthandthetestmustfirstpassdept-ifitisenabled,thenitwillpassstencil; – JanHus Mar23,2020at18:56 Addacomment  |  YourAnswer ThanksforcontributingananswertoStackOverflow!Pleasebesuretoanswerthequestion.Providedetailsandshareyourresearch!Butavoid…Askingforhelp,clarification,orrespondingtootheranswers.Makingstatementsbasedonopinion;backthemupwithreferencesorpersonalexperience.Tolearnmore,seeourtipsonwritinggreatanswers. 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