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Computer graphics & visualization Real-Time Pencil Rendering Marc Treib.

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Presentation on theme: "Computer graphics & visualization Real-Time Pencil Rendering Marc Treib."— Presentation transcript:

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

2 computer graphics & visualization Real-Time Pencil Rendering – 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 – Marc Treib 1 Introduction: Pencil Drawing

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

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

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

8 computer graphics & visualization Real-Time Pencil Rendering – 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 – 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 – 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 – 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 – 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 – Marc Treib 4.2 Implementation in Object Space Rendering: 6-way blending

14 computer graphics & visualization Real-Time Pencil Rendering – 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 – 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 – 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 – Marc Treib 5 Results

18 computer graphics & visualization Real-Time Pencil Rendering – Marc Treib 5 Results

19 computer graphics & visualization Real-Time Pencil Rendering – Marc Treib 5 Results

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

21 computer graphics & visualization Real-Time Pencil Rendering – 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 – Marc Treib Thanks for listening! Questions?

23 computer graphics & visualization Real-Time Pencil Rendering – 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, 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, 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, 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.


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