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Real-Time Rendering of Cartoon Smoke and Clouds Morgan McGuire Andi Fein Paulo Ferreira.

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Presentation on theme: "Real-Time Rendering of Cartoon Smoke and Clouds Morgan McGuire Andi Fein Paulo Ferreira."— Presentation transcript:

1 Real-Time Rendering of Cartoon Smoke and Clouds Morgan McGuire Andi Fein Paulo Ferreira

2 Gundam

3 Motivation Real-time cartoon rendering for: NPR Video Games Production Animation Preview Visualization Simulation and Training These often contain smoke, fluids, and other amorphous shapes…

4 Captain Marvel, June 1947 Marvel Comics 1947 Outlines Self- Shadowing Cel Shading

5 Heart of Empire Published by Dark Horse Comics 1999

6 SuperMan/Batman #16

7 Teenage Mutant Ninja Turtles Cartoon (2004)

8 Worms 4 (Game 2005)

9 Algorithm

10 Simulation Particle system Forces: Buoyancy Wind Drag Gravity Vortices Turbulence Size = smoke density ODE physics engine at 30 Hz Compressible: 100,000 particles Incompressible:1,000 particles

11 Simulation Use Particles from the game Avalanche

12 Simulation Instead of smoke and clouds, cartoon effect applied on the avalanche of the game

13 Rendering steps 1.Precomputed Nailboards 2.Outlines 3.Cel Shading 4.Shadows

14 Elements of Style Outlines Shading Self-Shadowing Steps

15 Nailboards

16 Normal-mapped Nailboards Precompute extended billboard textures Several puff orientations for variety Each particle is assigned one variation Normal Depth Color Opacity

17 Preprocessing step: Nailboard Create two textures to store data such as: unit camera-space surface normal N, signed camera space depth d, diffuse color C, and coverage mask alpha.

18 Outlines Edges of puff are deep and black ViewerActual Billboard Nailboard Depth Depth Color Black Shaded

19 Depth and Outline Pass Add d from the texture to the depth at the pixel and the depth buffer test automatically produces correct intersections.

20 Outlines Edges of puff are deep and black ViewerImage1 Nailboard

21 Outlines Edges of puff are deep and black Depth test suppresses excessive internal contours ViewerImage2 Nailboards No internal contour

22 Outlines Edges of puff are deep and black Depth test suppresses excessive internal contours Large depth discrepancy restores external contours ViewerImage3 Nailboards External contour distinguishing clouds

23 Outlines Use the alpha-shapes, which are slightly larger than the normal shapes, to create the outline, a flange of dark pixels slightly behind the billboard. The outline of these flange pixels is opaque because alpha is one, colored black because the C is black, and farther from the camera than the particle itself because d is zero.

24 Cel Shading Ambient: Gradient as function of y Diffuse:Arbitrary function, q(N · L) Pack both into a 2D texture, like X-Toon q = Example Lambertian Selle04 Two-Tone Three-Tone N · LN · L y

25 Explosion B & W q = Ambient

26 Explosion Color q = Ambient

27 Cel-Shading Pass Get N, C and alpha from the textures.

28 Cel-Shading Pass With ambient light color Ka, light color Kl, camera-space direction L to the light source, and diffuse color C from the texture map, the pixel at (x, y) is colored by a pixel shader using the following equation: N · LN · L y

29 Shadow Volumes 1.Compute the silhouette of the caster 2.Extrude this to form a polyhedron bounding the volume of shadowed space 3.Shadows are intersection between the volume and the scene

30 Billboard Shadows Caster is perpendicular to viewer and light Volume is a rectangular prism Four sides are parallel to the view vector Only 3 polygons to be rendered: one billboard and two shadow faces

31 Nailboard Shadows Apply the depth displacement to the shadow volume as well as the billboard Shadow volume visualization

32 Shadow Volume Visualization

33 Shadowing

34 Results

35 Train

36 Magic Lamp

37 Purple Cloud

38 Explosion

39 Varying Puff Shape

40

41

42 Video

43

44 Mimicking Artists

45 Lichtenstein Estate of Roy Lichtenstein 1963 Artist Algorithm

46 Context

47 Comparison Published by Dark Horse Comics 1999 AlgorithmArtist

48 50,000 particles 50,000 Particles on GeForce6800

49

50 Depth Differences Image space outlining method [ Saito and Takahasi ] Benefits: –Rendering time independent of the scene –Handles intersecting surfaces Drawbacks: –Can stall graphics pipeline –Assumes one style for the entire scene


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