SinglepassWireframeRenderingwithHiddenSurfaceRemoval

AndreasBrentzen,SteenLundNielsen,MikkelGjl,BentD.LarsenandNielsJrgenChristensen

Overview

Whatiswrongwiththetraditionaloffsetbasedmethodsforwireframedrawing?

Asinglepassmethodforwireframedrawingwithhiddensurfaceremoval.

Drawingprefilteredlines. Results Discussionandfuturework.

OffsetBasedMethods

Offsetbasedmethodshavetwopasses: Pass1:Drawmeshasfilledpolygons.

Zwriteandcomparisonenabled.

Pass2:DrawmeshaswireframewithZoffset.Zwritedisabled.Zcomparisonenabled.

Offsetensuresfilledpolygonsdonotoccludewireframe.

OffsetBasedMethods

Twotriangleswiththeiredgesdrawnusingnooffset,slopebasedoffset,constantoffset.

OffsetBasedMethods

uselinedrawingwhichisslow. areinherentlytwopass(evenslower) requireantialiasingtolookgood(slowerstill) haveartifactsbecauseitisimpossibletopickaperfectoffsetin

mostcases.

Admittedly,wecanlivewiththesemethods,butwedon'thaveto!

Approaches

Edgeisdrawnonlyifthepixelalreadycontainsafragmentfromthecorrespondingfilledpolygon.E.g.[Herreletal.1995].

Ourmethod:Drawwireframedirectlyasyouaredrawingfilledpolygon.Allinonepass.

SinglePassMethod

Foreachfragment,computecolorfromdistancetoclosestedge:

ComputingDistance

Weneed2Dwindowspacedistance. In2D,distancetolineisanaffinefunction. Linearinterpolationreproducesaffinefunctions.

ComputingDistances

Pervertex: Input:Allverticesof

triangle. Vertexshaderprojectsall

verticesoftriangle. Distancestoalledgesare

computed. Output:vectorofdistances

toallthreeedges.

ComputingDistances

Perfragment: Interpolatedistances.

Computecolorusingpreviousfragmentprogram.

Note:Thismethodextendstoquads.

PerspectiveCorrection

Oops!Graphicscardsperformperspectivecorrectinterpolation

However,itiseasytofix: Negateperspectivecorrection. WaitforD3D10orOpenGL3.0hardware.

Teapotusingourmethod...sofar.

Preintegratedlines

Colorisnowafunctionofdistance:

Teapotusingourmethod

SinglepassMethod

Detailofteapot Noticesmoothlines Perhapslinesarealittle

thick?

SinglepassMethod

Thinnerlinesareeasy. However,wetrade

thinnessforalittlealiasing.

Offsetbasedmethod

Constoffset=2000 Noticestippling Offsetcouldbechanged

butthereisnoperfectvalue

Offsetbasedmethod

Slopebasedoffset Noticedisocclusion

artefacts

Usedepthtofadeoutlinecolor.

Usedepthtodecidelinethickness.

Usealphatestingtoremoveinteriorofpolygon.

IndexedPrimitives

UsingthegeometryshadersofD3D10allowsustodrawwireframetrianglestrips.

LineStyles

Results

Performance

Themethoddoesnotsupportindexedgeometry Primitive/geometryshadersalleviatethis! Silhouetteedgesdrawnfromonesideonly Onlynoticeableonsmallmeshes Thisisessentiallyamethodfortrianglesand

quadrilaterals yesbutthatisaverycommonspecialcase

Issues

Merits

Methodisfast Singlepass Avoidslineprimitive Littleperfragmentcomputation

Highqualitylines Prefiltered NoZissues

Tweakable Manylinestylesarepossible

Thisisafutureworkteaser. Acknowledgements:

MarkHarris,NVIDIA,andPeterPikeSloan,Microsoft,wereveryhelpful.

MicrosoftmadeitpossibletotestthemethodonD3D10viaaWindowsVistaBeta.

Linetypes

4x4supersampling

Ourmethod PrefilteringwithGaussian