1. GPU Graftals: Stylized Rendering of Fluffy Objects Michael Lester

2. BACKGROUND

3. Adapting 2D fur techniques to 3D Easy to do in Film o fixed viewpoint o 1 vp per shot Difficult in interactive scenes o dynamic viewpoint How does the fur react to changes in camera position?

4. Possibilities Static Geometry Fur is represented in the 3D model itself Relatively inexpensive No easy fur animation No Level of Detail Not art-directable No control over fur Inflexible Dynamic Geometry Fur dynamically generated Potentially expensive Fur can be rendered in a separate style from model Easy to animate Art-directable Controllable (size, length,...) Flexible

5. What's a GPU Graftal? A Graftal is a small "fin" of geometry, many Graftals are used on an object to represent fur/complexity. (Introduced in Kowalski '99) A Graftal has many components: Position (on the object) Orientation Level-of-Detail Geometry Lines or "Strokes" Animation state Etc... GPU refers to the fact that these graftals are rendered entirely on the graphics processing unit.

6. Graftal Example

7. GPU GRAFTALS

8. Initial Graftal Placement Place a graftal at each vertex Graftal density depends on mesh Tons of room for improvement

9. Graftal Expansion Represented as a central “spine” –Blue points on the right Expanded to a 3D “fin” in a geometry shader Spinal representation allows for easy animation

10. Uniform Graftals Graftals placed at every vertex Graftals have uniform properties –Size, length, normal Looks interesting, but not artistic

11. Perturbed Graftals “Randomized” normals, sizes, lengths Looks more natural Not quite artistic –Too busy

12. Silhouette Graftals Scale graftals based on dot(Normal, View) Emphasize graftals on object edges –Efficiently! Notice the grid noise –Result of initial placement

13. Multiple Levels of Detail Graftals sorted into multiple Levels of Detail Based on dot(N,V) Rendered in different styles

14. Performance GeForce 8800 GTS (low-end) Frame Budget: 16ms for 60 fps 4ms is a valid graftal budget StagesTime (ms)# GraftalsTime/Graftal Culling0.370,000~ LOD Sort #10.135,000~ LOD Sort #20.135,000~ LOD Draw #14.710,000470 ns LOD Draw #21.32,700481 ns Total:6.5 ms70,00093 ns

15. Experiment Early Demo

16. The Problem The Question: o How do we represent furry or complex objects (like grass) in a stylized 3D scene? Answer: o Study traditional animation! The Challenge: o Applying animation techniques to 3D real-time rendering The Solution: o Graftals!

17. What's been accomplished thus far? GPU Graftal Implementation Research! Graftal system implemented completely on GPU o CPU independent o Only 1 draw() call required (per object) Complex model with >34,000 graftals Running at at ~300 fps o Compared to 2-4fps for the original paper Basic Graftal Level-of-Detail rules

18. What I plan to accomplish By the end of the quarter: Produce images comparable to the original paper Next quarter: Level-Of-Detail rules Individualized Graftals o Randomized size, shape, orientation... Customization system o Currently, complex shader code Fully polished example with several different classes of graftals o Furry creature in grass Initial Graftal distribution system o Even coverage, but no visible pattern

19. Demo! The strange spikes emerging from the rabbit are model errors The lines emerging from the rabbit are simple graftals (spline-only) Model is the famous "Stanford Bunny", courtesy of Stanford University