1. computer graphics & visualization Real-Time Pencil Rendering Marc Treib

2. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib Contents 1.Introduction: Pencil Drawing 2.Challenges 3.Contours 4.Interior Shading: Hatching 1.Object vs. Screen Space 2.Implementation in Object Space 3.Implementation in Screen Space 5.Results 6.Summary

3. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 1 Introduction: Pencil Drawing

4. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 1 Introduction: Pencil Drawing

5. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 1 Introduction: Pencil Drawing

6. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 2 Challenges Contours: – Errors in contours – Multiple trial-and-error lines Hatching: – Maintain constant stroke size – Continuously adjust stroke density – Align stroke direction with shape (curvature)

7. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 3.1 Contour Detection Object Space Approach: – But how to implement this?

8. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 3.1 Contour Detection Screen Space Approach: – Render depth and normals to textures – Apply edge detection algorithm (in a pixel shader) – Optionally: Object IDs (colors)

9. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 3.2 Contour Shaking Divide screen into regularly sized rectangles Perturb texture coordinates – E.g. with sine function + random offset Map contour image onto this distorted plane Repeat for multiple lines

10. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 4.1 Hatching: Object vs. Screen Space Object space approach: +Strokes stick to objects -Need to adapt stroke widths and densities with distance -Need continuous global parameterization Map textures containing pencil strokes onto objects, like conventional texture mapping

11. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 4.1 Hatching: Object vs. Screen Space Screen space approach: Map stroke textures onto objects in screen space +Easier control of stroke widths and densities -No object space continuity -Shower-door-effect

12. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 4.2 Implementation in Object Space Tonal Art Maps: Strokes in one image appear in all images to the right and down from it Store in 3d texture

13. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 4.2 Implementation in Object Space Rendering: 6-way blending

14. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 4.2 Implementation in Object Space To circumvent the need for a continuous global parameterization: Use Lapped Textures

15. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 4.3 Implementation in Screen Space Stroke textures: – Similar to object space approach, but dont need to bother with mipmaps

16. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 4.3 Implementation in Screen Space In the vertex shader: – Project 3d curvature direction onto screen space – Compute brightness In the pixel shader: – For each vertex, rotate texture coordinates to projected curvature direction – Blend 3 stroke textures (one per vertex)

17. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 5 Results

18. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 5 Results

19. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 5 Results

20. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 5 Results Demo!

21. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib 6 Summary Contours: – Edge detection using 2d image processing algorithm – Errors in contours by projecting onto distorted plane Interiors: – In object space: Tonal Art Maps, 6-way blending, Lapped Textures – In screen space: Rotate and map textures in screen space, 3-way blending

22. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib Thanks for listening! Questions?

23. computer graphics & visualization Real-Time Pencil Rendering – 2007-07-25 Marc Treib Bibliography Emil Praun, Adam Finkelstein and Hugues Hoppe. Lapped textures. In SIGGRAPH '00: Proceedings of the 27th annual conference on Computer graphics and interactive techniques, 2000. Emil Praun, Hugues Hoppe, Matthew Webb and Adam Finkelstein. Real-time hatching. In SIGGRAPH '01: Proceedings of the 28th annual conference on Computer graphics and interactive techniques, 2001. Matthew Webb, Emil Praun, Adam Finkelstein and Hugues Hoppe. Fine tone control in hardware hatching. In NPAR '02: Proceedings of the 2nd international symposium on Non-photorealistic animation and rendering, 2002. Hyunjun Lee, Sungtae Kwon and Seungyong Lee. Real-time pencil rendering. In NPAR '06: Proceedings of the 4th international symposium on Non-photorealistic animation and rendering, 2006.