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Real-Time Rendering of Cartoon Smoke and Clouds

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Presentation on theme: "Real-Time Rendering of Cartoon Smoke and Clouds"— 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 Outlines Cel Shading Self-Shadowing
 Marvel Comics 1947

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) Pre-rendered flat billboards Excessive detail
No self-shadowing

9 Algorithm

10 Simulation Particle system Forces: Size = smoke density
— 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 Precomputed Nailboards Outlines Cel Shading Shadows

14 Steps Elements of Style Outlines Shading Self-Shadowing

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 Black Nailboard Depth Shaded
Color Viewer Actual Billboard Depth

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 Viewer 1 Nailboard Image

21 Outlines Edges of puff are deep and black
Depth test suppresses excessive internal contours No internal contour Viewer 2 Nailboards Image

22 Outlines Edges of puff are deep and black
Depth test suppresses excessive internal contours Large depth discrepancy restores external contours External contour distinguishing clouds Viewer 3 Nailboards Image

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 y N · L Lambertian Selle Two-Tone Three-Tone q = Example

25 Explosion B & W Ambient q =

26 Explosion Color Ambient q =

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: y N · L

29 Shadow Volumes Compute the silhouette of the caster
Extrude this to form a polyhedron bounding the volume of shadowed space 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 Only ~300 polygons in this scene, including shadows

34 Results

35 Train

36 Magic Lamp

37 Purple Cloud

38 Explosion

39 Varying Puff Shape

40 Varying Puff Shape

41 Varying Puff Shape

42 Video

43 Video

44 Mimicking Artists

45 Lichtenstein Algorithm Artist  Estate of Roy Lichtenstein 1963

46 Context

47 Published by Dark Horse Comics 1999
Comparison Algorithm Artist

48 50,000 particles 50,000 Particles on GeForce6800 50,000 particles on GeForce6800; bus limited (factor of four is possible from clever encodings)


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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