1. Simulating Wax Crayons Dave Rudolf David Mould Eric Neufeld Depart. of Computer Science, U. of Saskatchewan

2. Overview Previous Work Goals Representation of Paper and Wax Interactions between Wax and Paper Rendering Results

3. Previous Work Adobe Photoshop TM Conté Crayon Filter

4. Previous Work Corel Painter TM Grainy Crayon Brush

5. Previous Work Viscous Paint Model (Baxter et al.)

6. Goals Improve realism Consider individual strokes Suitable paper texture Approximate mechanics of crayons Simulate optical properties of wax Efficient Rendering Not too insanely realistic

7. Representation of Paper Height-Mapped Texture Texture Synthesis Other sources (scans of Real Paper)

8. Convolution Mask 0 0 0 0 0 1 1 1 0 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 1 0 0 1 1 1 1 1 1 0 0 1 1 1 1 1 1 1 0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Somewhat Expensive Can be Pre-computed Van Wilk’s Lunar Texture

9. Other Textures Make no assumptions about texture

10. Representation of a Crayon 2D Mask Height Area

11. Compression of Wax

12. Assume that wax compresses linearly Hooke’s Law: F = Y  L A / L 0 Can’t solve directly Crayon & Paper profiles are not predictable Must binary-search for force ( F )

13. Compression of Wax

14. Wax Deposition

15. Determined by: Friction Force of Crayon Direction of Stroke Whether there is existing wax F f =  F n =  N cos(N, F c )

16. Wax Smearing

17. Depends on texture and crayon force Flow Smearing Independent of crayon heading S f xy =   z Directional Smearing Depends on crayon heading S d xy =  cos( (x, y), V )

18. Deposition and Smearing Without Smearing With Smearing

19. Rendering Need a good colour model Wax scatters and absorbs light Additive/Subtractive models are insufficient Kubelka-Monk Colour Model Approximates of Translucent Pigments Considers transmittance, scattering, and interference of pigment layers.

20. Approximated Kubelka-Monk Real Crayon Generated Crayon

21. Results Not Quite Interactive Between 0.3 and 2.0 seconds per frame Updating model takes the most time Not Quite Realistic No wax flaking, carving, transporting

22. Results

25. Questions ?