Real-time Rendering of Woven Clothes

Neeharika Adabala∗

MIRALab-University ofGeneva,

24 rue du General Dufour,CH1211, Geneve-4,

Switzerland

NadiaMagnenat-ThalmannMIRALab-University of

Geneva,24 rue du General Dufour,

CH1211, Geneve-4,Switzerland

Guangzheng Fei†

Institute of SoftwareChinese Academy of Sciences

ABSTRACTVirtual environments containing humans moving and per-forming actions in real time are ubiquitous in computergraphics applications. Such characters are often clothed inwoven fabrics. This paper presents a technique for visualiz-ing woven clothes in real time, while optimizing the realis-tic appearance. The proposed approach supports renderingof complex weave patterns by adopting Weaving Informa-tion File (WIF), a standard from textile Computer AidedDesign (CAD) for representing the grammar of weaving.We develop a realistic rendering scheme by combining thegrammar representation obtained from the WIF with a pro-cedural thread texture, a suitable cloth Bi-directional Re-flectance Distribution Function (BRDF) and horizon maps.We employ the multi-texturing approach to meet the realtime constraint. Thus our approach to visualizing wovenclothes begins from weaving grammar specifications and con-verts them into textures that can be applied on clothes. Wedemonstrate the versatility of the proposed approach withexamples.

1. INTRODUCTIONSeveral applications of virtual reality involve creating en-

vironments populated by virtual human beings performingvarious actions in real-time. These virtual humans are oftenclothed in woven or knitted fabrics. In order to create arealistic experience of Virtual Reality there is a need to beable to visualize the clothing realistically.

There are two main aspects to the problem of creatingclothing in computer graphics:

• Modelling the dynamics of clothes: Clothes are flexi-

∗Current Affiliation: Department of Computer Science, Uni-versity of Central Florida, Orlando, USA†This work was done when at MIRALab

ble, hence when people move the clothes exhibit dy-namic behavior. This is a very important character-istic of clothes and a large body of research has beendone in the area of modelling dynamics of clothing [15],[3]. Most of these techniques are non real-time, how-ever recent work [4] has made it feasible to simulatethe clothing dynamics in real time.

• Visualizing clothes: Clothes exhibit micro and macro-geometry (we refer to milli-scale geometry as macro-geometry in this paper). The light interaction withthe interwoven threads has to be captured in order tocreate a realistic appearance.

This paper focuses on the second aspect namely visualizingclothes. Our goal is to create a real time technique thatenables rendering of complex weave patterns.

There are two main types of clothes namely, the knitwearand woven clothes. Impressive results have been reportedin recent research in visualization of knitwear [19], [5], [17].Techniques to represent complex knit patterns have beendeveloped [19]. Relatively less work has been done in thearea of woven clothes, especially in the context of represent-ing complex weave patterns. The main issues that have tobe addressed when developing a technique for visualizingclothes are:

• Representation of interwoven threads

• Modelling of light interaction with the threads/cloth.

We briefly describe some of the previous work in the lightof these issues. Westin et al. [16] consider a weave pat-tern and obtain realistic rendering of cloth. In this workthey consider a simple alternate weave pattern known as thelinen binding and model the illumination at micro-scale andextend it to the milli-scale by performing an integral overthe surface. Yasuda et al. [18] describe a shading modelfor clothes that emphasizes on the interaction of light withindividual fibers that constitute the cloth. Groller et al.[10] use a technique based on three-dimensional textures tomodel textiles. More recently, Daubert et al. [5] have pre-sented an efficient technique for modelling and renderingclothes, their approach is applicable especially for coarselywoven fabric and knitted fabric. Drago and Chiba [6] de-scribe a method of procedurally generating the appearanceof interwoven structures and animating them.

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Apart from the work that directly addresses the problemsof rendering clothes there is a class of work based on lightinteraction with surfaces that exhibit micro-geometry thatcan be applied to address problems in rendering of clothes.These include the work by Ashikhmin et al. [2] that devel-ops a micro-facet based technique for modelling light inter-action with surfaces and applies it effectively to simulate theappearance of velvet and satin. Also the techniques of illu-minating micro-geometry described in Heidrich et al. [11]and Sloan et al. [14] find direct application to visualizationof clothes as they exhibit micro-geometric details.

All the existing techniques are very powerful and solve theproblem of visualizing clothes effectively, but to the best ofour knowledge the existing techniques do not address theproblem of being able to capture a wide variety of weave pat-terns. Some variations other than the most common linenbinding have been considered in Ashikmin et al. [2], Daubertet al. [5] and Drago and Chiba [6] where patterns similarto satin or twill are considered. However the more complexones have not been addressed. More recently Glassner [7,8, 9]has discussed the richness of patterns possible by usingthe ideas from weaving. However none of the existing tech-niques can be used to generate the appearance for complexweave patterns.

The goal of our technique is to provide graphics designerswith the capability of generating textures with various weavepatterns to texture the clothes designed. The alternate ap-proaches to address this problem that depend on photogra-phy/scans of material suffer from the problem of presenceof features resulting from the illumination under which thephotographs/scans were acquired. We require textures withthe capability to exhibit the change in illumination behav-ior without the illumination model being incorporated intothe color of the material. Also, viewing of cloth at close dis-tances without loss in realism should be feasible. In order toaddress these issues we break up the problem of visualizingclothes into:

• Representing the weave pattern

• Modelling the microstructure of the threads that makethe cloth

• Modelling the light interaction with the cloth:

– Reflection behavior

– Shadowing behavior between the threads in theweave pattern.

Our approach addresses the above issues as follows: Wehave used the standard in the textile industry known asthe Weaving Information File (WIF) to obtain the complexweaving patterns and represent them suitably for generat-ing the color texture. The microstructure of the threads isincorporated into a procedural texture and it is used alongwith the WIF information to generate a color texture. TheWIF information is used to define a suitable BRDF thatcorresponds to the average expected reflection behavior ofthe cloth. The shadowing that occurs between the threadswhen they are woven together is captured into horizon mapsthat are generated with information from the WIF. Thus,we are able to start from the grammar representation forweaving a cloth and generate a visualization of the wovencloth.

The organization of the paper is as follows: the section2 gives an overview of our algorithm. The details of thefour main parts of our algorithm are described in section 3.We discuss the results in section 4 by presenting exampleimages that demonstrate the capabilities of our algorithm.Conclusions and suggestions for future work are given insection 5.

2. OVERVIEW OF THE ALGORITHMThe outline of the algorithm is presented in Figure 1.

Figure 1: Outline of technique.

The information in the WIF describes the weave pattern.This is interpreted by the WIF interpreter and made avail-able to the modules namely: the micro-geometry shader, theBRDF generator and the horizon map generator.

The micro-geometry shader makes use of a proceduralthread texture generator to create a color texture based onthe WIF. The procedural thread texture generator is respon-sible for creating the shading that results from the twistingof the threads.

The BRDF generator takes as input the average charac-teristic of the cloth that can be obtained from the weavepattern described in the WIF. It generates a BRDF to cor-respond to these characteristics. It should be noted thatthe WIF does not contain any properties that describe theillumination characteristics of the thread so a technique ofmodelling the interaction of light only based on the infor-mation present in the WIF is not complete. However, thepattern of weaving contributes significantly to the way thelight interacts with a fabric. This is very well exemplifiedby the fact that very different material fibers when wovenusing the satin binding pattern result in a material with aglossy appearance.

The WIF contains the weave grammar and therefore fromthis information it is possible to learn which facets of thethreads are longer and hence tend to be higher on the surfaceof the cloth. This in turn dictates how such facets of clothcast shadows on the neighboring threads of the cloth. The

horizon map generator module uses the WIF information todefine these shadows that are essential to convey the feelingof depth in the weave pattern.

The real time constraint prompted us to use the multi-texturing approach to realize the solution to our algorithm.Each of the above modules results in a texture and the finalrendering of the cloth is done by compositing the textures.

In the following section we describe in detail each of themodules of the algorithm.

3. DETAILS OF THE ALGORITHMThe four main modules of our approach namely the WIF

interpreter, the micro-geometry shader, the BRDF gener-ator and the horizon map generator are described in thissection.

3.1 WIF interpreterWoven fabrics exhibit well-defined structures, it should

be possible to use a procedural or grammar-based techniqueto represent the weave pattern. However, the wide vari-ety of the weave patterns limits the applicability of suchtechniques. Fortunately, in CAD of textile there is a well-established technique for representing the weave pattern asWIF format [13]. It is a specification that provides the in-formation required for weaving a fabric in the real-world.The WIF includes information from which a grammar canbe derived to indicate how warp and weft threads are inter-woven.

Since the WIF format was designed for manufacturingpurpose rather than for visualization, it is not directly appli-cable to computer graphics. The WIF contains the thread-ing information that defines which warp thread goes throughthe heddle in which shaft. It also contains a liftplan whichrepresents the combination of shafts raised for creation ofeach weft. The weave pattern can be obtained by combin-ing the threading and the liftplan information. We parsethe WIF format and derive the weave pattern from it. Theweave pattern is represented as a two dimensional matrix,where the rows and the columns can be thought of to indexthe weft and warp threads respectively. Each entry in thematrix indicates the visibility of the weft or warp thread atthat point. The dimension of the matrix is determined bythe number of weft and warp threads present in the weavepattern.

The WIF format also contains color information for eachthread that can be directly combined with the pattern ma-trix to generate the color scheme for the weave pattern.Since the weave pattern matrix indicates which thread isseen at each point on one face of the cloth, the texture forthe other side of the cloth is easily obtained by complement-ing the matrix. Figure 2 shows a color scheme of a complexweave pattern generated from a WIF format.

3.2 Micro-geometry shaderThe woven fabrics are made up of interwoven twisted

fibers. We have observed that when one examines wovenclothes at the usual distances of viewing the twisted natureof the thread facets is often visible. The visibility is causedby the presence of dark shaded lines that follow the twist ofthe fibers of the thread. In some cases these lines are seenprominently while in other cases they are less prominent.It is possible to discern whether the threads are tightly orloosely twisted from these shaded lines. We also observed

Figure 2: Example color scheme of a weave pattern.

Figure 3: Output of procedural texture (a) Veryloosely twist of thread without shading, (b) Moretightly twisted thread, noise is added to simu-late the presence of fibers about the thread, (c)Thicker fibers twisted into thread, (d) Tightlytwisted thread.

that the shading present on the thread facet tends to re-main approximately the same under various lighting condi-tions. We may attribute this to presence of deep fine grovebetween the twists of the fiber into which the light neverreaches. This feature is unlike the other illumination aspectsof the macro-geometry of clothes in the form of shadowingbetween the threads that show variation with position oflight. Also unlike wool where the fibers occupy a significantvolume, the threads that are woven into a cloth are finerand are limited to a near two-dimensional surface.

The above observations lead us to separate the micro andmacro- geometry details present in the woven clothes. Weexploit the near two-dimensional nature of the cloth surfaceby modelling the facet of thread visible on the surface of acloth as a two dimensional procedural texture. We designthe procedural texture such that it has parameters to cap-ture the tightness of the twist and thickness of the thread.Figure 3 shows examples of the thread shading texturesthat are generated procedurally by our technique.

These thread textures can be used along with the weavepattern to generate a color texture of a weave pattern thathas the appearance of being woven from twisted fibers. Anexample of such a texture is shown in Figure 4.

The gaps in the threads are created creating an RGBAtexture map with alpha equal to one in the gaps. The alphavalue reduces at silhouettes due to mipmapping, however itdoes not completely reduce to zero at graze angles. It is pos-sible to implement this variation by introducing dependenceof alpha on angle between viewing and normal direction.

Figure 4: Example color texture generated for thecolor scheme presented in Figure 2.

This dependence has not been incorporated in the currentimplementation.

3.3 BRDF generatorThe image that is generated by combining the micro-

geometry shader and the weave pattern does not includean illumination model. It only contains the colors of thethreads and the pattern of weaving. However, the sameweave pattern can have a significantly different appearancebased on the material of the threads that constitute theclothes. Also, the same threads can result in a different tex-ture of the cloth depending on the weave pattern, this hasalready been pointed out before when it was mentioned thatuse of the satin weaving approach results in a more glossytexture for the same fibers as compared to a linen bindingapproach.

In our technique the BRDF generator makes use of theWIF information to define a BRDF. Various approaches torepresent the BRDF can be adopted. We choose the micro-facet based BRDF modelling [2] because it is flexible and canbe used to model complex reflection behavior. In this ap-proach design of suitable probability distribution functionsof micro-facet enables modelling of various types of textures.

The micro-facet based BRDF [2] is given by the equation:

Ψ(~win, ~wout) =p(~h)〈(~h · ~n)〉F ((~h · ~win), λ)

4g(~win)g(~wout)(1)

where ~win is the in coming light direction, ~wout is the view-

ing direction, ~h is the half way vector give by ~win+ ~wout, p(~h)is the probability distribution of micro-facets in the direction

of the half way vector ~h. The term 〈(~h · ~n)〉 is the ensembleaverage of the half-way vectors in the hemisphere containingthe normal to the surface this term accounts for the pro-

jected area of the micro-facets. F ((~h · ~win), λ) is the Fresnelcoefficient given by the standard Fresnel equation used ingraphics. At near perpendicular angles of incidence influ-ence of warp color is incorporated in defining the λs whileat grazing angles the weft color is made to dominate the def-inition of the λs in the Fresnel equation. This is achieved byweighting the color influence based on the viewing and lightincidence directions. This approach is needed as warps areless visible at grazing angles, because they usually occupya slightly lower plane than the wefts due to the nature ofthe weaving process. The functions g( ~win) and g(~wout) arethe shadowing functions that account for the obstruction ofsome of the micro-facets in the light and viewing directions.They are defined [2] by the following equation:

g(~w) =

∫W+

(~h · ~w)p(~h)dW+ (2)

where the integral is over W+ the hemisphere over the di-

rections in which (~h · ~w) are positive.

The probability distribution of the micro-facets p(~h) is themost crucial element of the above definition as it is responsi-ble for modelling the appearance of the material. We define

p(~h) for a cloth as follows:

p(~h) = fwarp ∗ pwarp(~h) + fweft ∗ pweft(~h) (3)

where p(~h) represents the probability distribution of the nor-mals of the micro-facet, fwarp and fweft are respectivelythe fractions of the surface occupied by the warp and weftthreads. The probability distributions of facets on individ-

ual warp and weft threads are given by the pwarp(~h) and

pweft(~h) respectively. The above equation (3) is a general-ization of the probability distribution used in [2] for satin.

The probability distributions of the micro-facets on indi-vidual threads in the warp and weft directions, namely the

functions for pwarp(~h) and pweft(~h) are defined as cylindri-cal Gaussian with σy = ∞ similar to the one described in [2]for this purpose. The width of the thread is used to choosethe σx of the cylindrical Gaussian.

We achieve the real-time rendering of the BRDF by usingthe cube map approach [12]. The BRDF we use is definedfor the whole cloth rather than for individual thread seg-ments therefore some details like shadowing of threads oneach other are not captured by it. These details are cap-tured in the horizon maps that are described in the nextsection.

3.4 Horizon map generatorHorizon maps store shadows cast by small surface pertur-

bations on itself. In the case of fabrics in outdoor day lightscenes this feature is relatively less important as there is alarge amount of light incident on the fabric from all direc-tions resulting in the absence of shadowing among threads.However, in the case of artificial lighting in indoor sceneswe have observed that the fabrics tend to look significantlydifferent under lighting and this is due to the shadows castby the threads on each other.

We observe that the height of a facet of thread abovethe cloth surface is dependent on the length of the facet onwhich it occurs. However, the height is limited to a maxi-mum level dictate by the tightness of the weave. This heightin turn defines the shadow that it can cast on the neighbor-ing thread facets. The WIF information in the form of theweave pattern matrix is used to compute the length of thefacet at each location within the weave. This informationis then translated into a height field that is further used tocompute the horizon maps. We discretize the directions ofthe light and generate a shadow map for each of the direc-tions. This approach is less accurate than the techniquesproposed in [11] and [14], however we found that it givesreasonable results for our real time constraints.

4. RESULTS AND DISCUSSIONThis section presents example images that have been gen-

erated using our technique.We implement out algorithm on a PC with a pentium

4 processor (2 GHz), with a nVIDIA graphics card. Theclothes that have been rendered in this section were mod-

Figure 5: Versatility of the approach for generation of various weave patterns. The jacket on the right istextured by the weave pattern presented in Figure 4.

elled with MIRACloth, the in house software of MIRALabfor designing clothes. All the models in the figures consist ofapproximately 2000 triangles each. We perform the compu-tation of the color texture, BRDF texture and the horizonmaps as a preprocessing step. The computation time forthe color texture is less than one second and each of theshadow maps takes about half a second. The BRDF com-putation along with the separation for cube maps requiresaround 140 seconds. The rendering of the images from thesepre-computed textures using multi-texturing is achieved inreal time.

Figure 6: Directional dependence of the appearanceof cloth when contrasting colored threads are woventogether.

Figure 6 demonstrates the ability of our technique to han-

dle directional dependence of the appearance of cloth whentwo very contrasting colored threads are woven together. Ascan seen the cloth appears bluish in the perpendicular viewdirection while it appears more reddish at grazing angles.

The variation in appearance of the texture of the cloth canbe observed in the images of the dress presented in Figure 7.The image on the left is generated with a BRDF of cottonwhile that on the right is generated with a BRDF of satin.These images have been generated to highlight the range ofappearances that can be created by proper design of BRDF.However in the case when we derive the BRDF from the WIFwe obtain a BRDF that is related to the weave, which neednot directly appear more like satin or like cotton. It typicallyappears somewhere in between, more like satin in the casewhen either large weft or warp facets dominate the surfaceof the cloth and more like cotton when the warp and weftfacets are small and equally distributed. It should be notedthat the weave pattern alone does not control the glossyappearance of the cloth there are certain other parameterslike the micro-facet distribution on the threads, as describedin section 3.3 which control the appearance of the fabric.Notice the slight transparency in the material resulting fromthe gaps in the weave. This appearance of transparencyincreases with increase in gap size.

We demonstrate the ability of our technique to enable usto zoom into any level of detail in the Figure 8. It can beseen that our technique results in a very realistic appearanceof the cloth even at close distances. The presence of shadowsenhances the feeling of thickness of the cloth.

We present more example images of jackets created fromvarious weave patterns in Figure 5. It can be inferred fromthe wide variety of weave patterns that we have applied togenerate the images in figures 5 to 8, that use of the WIFbased method enables easy generation of many complex andinteresting weave patterns. This provides the graphics com-munity with the ability to generate all kinds clothes withdesigns created in weave.

We include animations to demonstrate the satin BRDFand the ability to zoom in on the cloth and perceive detailsof the cloth including the thread twist.

5. CONCLUSIONS AND FUTURE WORKThis paper has proposed a technique for generating real-

istic visualization of cloth in real-time. The main features

Figure 7: Comparison of satin and cotton BRDF. The dress on the left is generated with cotton BRDF whilethat on the right is generated with a satin BRDF.

of the work are:

• Texture of fabric generated from grammar: Thisgave us the capability to create a wide variety of com-plex weave patterns that was not possible previously.

• Compatible with textile CAD: Use of the WIFformat that has been a standard in the textile indus-try from 1996, makes our work compatible with workcarried out in the textile industry and thus helps tobridge gaps between related areas.

• Micro and Macro detail separation: In order tomeet the real time constraint and also not lose thedetails in modelling the cloth, we separated details ofthe cloth visualization into micro and macro details.The micro details were incorporated into the threadtextures that were generated procedurally while themacro details were incorporated into the BRDF andhorizon maps.

• Weave pattern based BRDF: The ability to repre-sent the weave as a grammar enabled us to define theBRDF based on the pattern.

• Works in real time: The multi-texturing approachwas exploited to develop an algorithm that works inreal-time.

While the algorithm described in the paper gives realisticresults, the BRDF technique presented in the paper makesuse of the average behavior of the weave pattern, howeverit may be possible to investigate a more detailed model ofthe BRDF based on the grammar of weaving at distinctlocations within the textile [1]. Such studies can lead to aBi-Directional Texture Function (BTF) representation forthe cloth. One of the important features of cloth that hasnot been captured is the presence of fibers on the surfaceof the cloth. Techniques based on special processing at thesilhouette to incorporate this feature can be investigated.

6. ACKNOWLEDGEMENTSThe authors are grateful to Christiane Luible for providing

the model of the clothes used in the Figures 5 to 8. Partof this work has been supported by the European projectMELIES IST-2000-28700.

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Figure 8: Illustration of ability to zoom in on detail. The image on the top right gives the weave patternused to texture the dress. Notice the realistic appearance when viewed at close range.

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