Computer graphics & visualization Real-Time Pencil Rendering Marc Treib.
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Transcript of Computer graphics & visualization Real-Time Pencil Rendering Marc Treib.
computer graphics & visualization
Real-Time Pencil Rendering
Marc Treib
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc Treib
Contents1. Introduction: Pencil Drawing2. Challenges3. Contours4. Interior Shading: Hatching
1. Object vs. Screen Space2. Implementation in Object Space3. Implementation in Screen Space
5. Results6. Summary
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc Treib
1 Introduction: Pencil Drawing
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc Treib
1 Introduction: Pencil Drawing
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc Treib
1 Introduction: Pencil Drawing
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc 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)
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc Treib
3.1 Contour Detection• Object Space Approach:
– But how to implement this?
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc 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)
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc 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
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc 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
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc 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“
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc 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
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc Treib
4.2 Implementation in Object Space• Rendering:
6-way blending
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc Treib
4.2 Implementation in Object Space• To circumvent the need for a continuous global
parameterization:Use Lapped Textures
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc Treib
4.3 Implementation in Screen Space• Stroke textures:– Similar to object space approach, but don‘t need to
bother with mipmaps
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc 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)
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc Treib
5 Results
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc Treib
5 Results
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc Treib
5 Results
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc Treib
5 Results
Demo!
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc 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
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc Treib
Thanks for listening!Questions?
computer graphics & visualization
Real-Time Pencil Rendering – 2007-07-25Marc 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.