NPR TodayReal–Time HatchingHatchingGoalPrevious WorkSlide 6Overall ApproachTonal Art MapsGenerating Tonal Art MapsSlide 10Even Spacing of StrokesSlide 12RenderingContinuityTexture BlendingSlide 16Texturing Arbitrary SurfacesSlide 18Direction FieldFuture WorkFine Tone Control in Hardware HatchingSlide 22HijackGL: Reconstructing Streams for Stylized RenderingMotivationSlide 25AlgorithmIntercepting OpenGLReconstructing GeometrySlide 29Slide 30Slide 31Slide 32ExamplesWireframe RenderingPencil Sketch RenderingBlueprint RenderingCartoon RenderingModel CapturingCapabilities and LimitationsSlide 40QuestionsSlide 42WYSIWYG NPR: Drawing Strokes Directly on 3D ModelsGoalsSlide 45How It WorksAn ExampleSlide 48StrokesStroke VisibilityPaper TexturesBase CoatDecals and CreasesStroke SynthesizingSlide 55SilhouettesSlide 57Picture ExamplesSlide 59Slide 6004/06/05 © 2005 University of WisconsinNPR Today•“Real–Time Hatching”, Emil Praun, Hugues Hoppe, Matthew Webb and Adam Finkelstein, SIGGRAPH 2001•“HijackGL: Reconstructing Streams for Stylized Rendering”, Alex Mohr and Michael Gleicher, NPAR 2002•“WYSIWYG NPR: Drawing Strokes Directly on 3D Models”, Robert D. Kalnins, Lee Markosian, Barbara J. Meier, Michael A. Kowalski, Joseph C. Lee, Phillip L. Davidson Matthew Webb, John F. Hughes and Adam Finkelstein, SIGGRAPH 200204/06/05 © 2005 University of WisconsinReal–Time HatchingEmil Praun, Hugues Hoppe, Matthew Webb Adam FinkelsteinPresented by Kael Greco04/06/05 © 2005 University of WisconsinHatchingGroups of strokes with spatially coherent direction and quality Hatching conveys:•Lighting•Material Properties/Surface Texture•Shape/Volume04/06/05 © 2005 University of WisconsinGoalRendering of 3D models in a real-time non-photo realistic style based on hatching04/06/05 © 2005 University of WisconsinPrevious WorkReal-Time Hatching–Screen-space “filter” [Lake et al. 2000]–Fixed density strokes [Elber ’99]04/06/05 © 2005 University of WisconsinPrevious Work•Prioritized Stroke Textures[Salisbury et al. ’94][Winkenbach et al. ’94]•Art Maps[Klein et al. 2000] tone  scale 04/06/05 © 2005 University of WisconsinOverall ApproachSet of texturesMeshPreprocessResultReal-TimeExample stroke04/06/05 © 2005 University of WisconsinTonal Art Maps•Collection of stroke images•Will blend (design with high coherence)•Stroke nesting propertytonescale04/06/05 © 2005 University of WisconsinGenerating Tonal Art MapsSet of texturesMeshPreprocessResultReal-TimeExample stroke04/06/05 © 2005 University of WisconsinGenerating Tonal Art Maps•Draw or import bitmap for one stroke•Automatically fill TAM with strokes–When placing stroke in an image,add it to all finer & darker images–Fill table column by column, coarse to fine–Space strokes evenly04/06/05 © 2005 University of WisconsinEven Spacing of Strokes•Choose best stroke from large candidate pool•Fitness = uniformity & progress towards tone•Keep Gaussian pyramid for all TAM images1 TAM column(same tone)04/06/05 © 2005 University of WisconsinEven Spacing of StrokesFor each candidate stroke si:For the hatch image at each level l of the TAM that would receive siFind cumulative effect of adding si at all levels p of the pyramid.Tpl = average tone of hatch image drawn with all previous strokes Tipl=average tone with si addedNormalize “goodness” by stroke lengthDarkness that this stroke would add to all the hatch images in this column04/06/05 © 2005 University of WisconsinRenderingSet of texturesMeshPreprocessResultReal-TimeExample stroke04/06/05 © 2005 University of WisconsinContinuitySpatial Discontinuity–Temporal continuity: no “popping” •Stroke size continuity maintained by mipmapping•Tone continuity maintained by blending textures–Spatial continuity: same contribution for a texture on both sides of an edge04/06/05 © 2005 University of WisconsinToneTonevv11vv22vv336-Way BlendFinalTexture Blending04/06/05 © 2005 University of WisconsinTexture Blending•Pack grayscale tones in R,G,B channels→ 6 tones in 2 textures•Use multitexture engine→ single-pass 6-way blend•Vertex programs compute blend weights→ static vertex data !!VP1.0 #Vertex Program for Real-Time Hatching.//output vertex homogeneous coordinatesDP4 R2.x, c[0], v[OPOS];DP4 R2.y, c[1], v[OPOS];DP4 R2.z, c[2], v[OPOS];DP4 R2.w, c[3], v[OPOS];MOV o[HPOS], R2; //stroke texture coordinates, transformedDP3 o[TEX0].x, c[4], v[TEX0];DP3 o[TEX0].y, c[5], v[TEX0];DP3 o[TEX1].x, c[4], v[TEX0];DP3 o[TEX1].y, c[5], v[TEX0];// splotch mask coordinates MOV o[TEX2], v[TEX0]; //get the Gouraud shadeDP3 R1, c[8], v[NRML]; //apply clamp-linear tone transfer functionMUL R1, R1, c[9].x;ADD R1, R1, c[9].y;MAX R1, R1, c[9].z;MIN R1, R1, c[9].w;//now look up the weights for the TAMs blendingEXP R2.y, R1.x; //frac(tone)ARL A0.x, R1.x;MOV R3, c[A0.x + 10];MAD R3, -R2.y, R3, R3; MAD o[COL1], R2.y, c[A0.x + 11], R3; MOV R4, c[A0.x + 20];MAD R4, -R2.y, R4, R4;MAD o[COL0], R2.y, c[A0.x + 21], R4;END04/06/05 © 2005 University of WisconsinTexturing Arbitrary SurfacesTonal Art MapLappedtexturePreprocessMeshResultReal-TimeExample stroke04/06/05 © 2005 University of WisconsinTexturing Arbitrary Surfaces•Lapped Textures[Praun et al. 2000]04/06/05 © 2005 University of WisconsinDirection Field•Based on surface principal curvatures•Optimized to be smooth–[Hertzmann & Zorin 2000]–Symmetry: 180º instead of 90º–Sample on faces04/06/05 © 2005 University of WisconsinFuture Work•Stroke Growth•More general TAMs•View-dependent stroke direction•Automatic indication04/06/05 © 2005 University of WisconsinFine Tone Control in Hardware HatchingScheme 1Scheme 2Matthew Webb, Emil Praun, Adam Finkelstein, Hugues HoppeNPAR 2002 Proceedings04/06/05 © 2005 University of Wisconsin04/06/05 © 2005 University of WisconsinHijackGL: Reconstructing Streams for Stylized RenderingAlex Mohr and Michael Gleicher04/06/05 © 2005 University of WisconsinMotivation•NPR techniques are different then traditional •Applications must be architected to fit new NPR styles•Non-invasive methods•Altering a graphics application without modifying source code •Provides new functionality to a program •Explore potential for creating new and interesting visual styles04/06/05 © 2005 University of WisconsinPrevious Work•Concept of non-invasive stylization of interactive